# pos

id: cord-026010-61j07gq3
pos: NNP
token:
  ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ

lemma:
  ÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐÐ


# bib

id: cord-001082-sufwsu77
author: Bär, Séverine
date: 2013-09-19
txt: ./txt/cord-001082-sufwsu77.txt
cache: ./cache/cord-001082-sufwsu77.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3777860/
doi: 10.1371/journal.ppat.1003605
summary:
  By colocalization with cellular marker proteins and specific modulation of the pathways through over-expression of variant effector genes transduced by recombinant adeno-associated virus vectors, we show that progeny PV particles become engulfed into COPII-vesicles in the endoplasmic reticulum (ER) and are transported through the Golgi to the plasma membrane. Moreover, a very limited reduction of secreted particles was observed with dnRab11, and nothing at all upon inhibition of Rab8, suggesting that PV particles take a different route from the Golgi apparatus to the plasma membrane as compared to GLuc. Due to their impact on MVM plaque morphology in A9 cells, the ERM family proteins moesin (Moe) and radixin (Rdx) have been implicated in the spreading capacity of this parvovirus [38] .

title:
  Vesicular Transport of Progeny Parvovirus Particles through ER and Golgi Regulates Maturation and Cytolysis

abstract:
  Progeny particles of non-enveloped lytic parvoviruses were previously shown to be actively transported to the cell periphery through vesicles in a gelsolin-dependent manner. This process involves rearrangement and destruction of actin filaments, while microtubules become protected throughout the infection. Here the focus is on the intracellular egress pathway, as well as its impact on the properties and release of progeny virions. By colocalization with cellular marker proteins and specific modulation of the pathways through over-expression of variant effector genes transduced by recombinant adeno-associated virus vectors, we show that progeny PV particles become engulfed into COPII-vesicles in the endoplasmic reticulum (ER) and are transported through the Golgi to the plasma membrane. Besides known factors like sar1, sec24, rab1, the ERM family proteins, radixin and moesin play (an) essential role(s) in the formation/loading and targeting of virus-containing COPII-vesicles. These proteins also contribute to the transport through ER and Golgi of the well described analogue of cellular proteins, the secreted Gaussia luciferase in absence of virus infection. It is therefore likely that radixin and moesin also serve for a more general function in cellular exocytosis. Finally, parvovirus egress via ER and Golgi appears to be necessary for virions to gain full infectivity through post-assembly modifications (e.g. phosphorylation). While not being absolutely required for cytolysis and progeny virus release, vesicular transport of parvoviruses through ER and Golgi significantly accelerates these processes pointing to a regulatory role of this transport pathway.


id: cord-003761-ikni2acz
author: Li, Zengbin
date: 2019-06-04
txt: ./txt/cord-003761-ikni2acz.txt
cache: ./cache/cord-003761-ikni2acz.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6630369/
doi: 10.3390/v11060510
summary:
  In this review, we mainly summarize recent research data on the viroporin or viroporin-like activity of 2B proteins, which affects the biological function of the membrane, regulates cell death, and affects the host immune response. In particular, the 2B protein may change the Ca 2+ concentration to regulate autophagy and apoptosiswhich are distinct cell death mechanisms controlled by the virus to effectively evade the host immunity, thereby promoting viral replication and release [48] [49] [50] [51] [52] . Thus, the main points of focus for research on the structure and function of the 2B protein toward ultimate drug development are: (1) mechanism of increasing membrane permeability to disturb the ion balance, (2) regulation of autophagy and apoptosis, (3) inhibition of the host immune response, and (4) promotion of viral replication and release.

title:
  Biological Function and Application of Picornaviral 2B Protein: A New Target for Antiviral Drug Development

abstract:
  Picornaviruses are associated with acute and chronic diseases. The clinical manifestations of infections are often mild, but infections may also lead to respiratory symptoms, gastroenteritis, myocarditis, meningitis, hepatitis, and poliomyelitis, with serious impacts on human health and economic losses in animal husbandry. Thus far, research on picornaviruses has mainly focused on structural proteins such as VP1, whereas the non-structural protein 2B, which plays vital roles in the life cycle of the viruses and exhibits a viroporin or viroporin-like activity, has been overlooked. Viroporins are viral proteins containing at least one amphipathic α-helical structure, which oligomerizes to form transmembrane hydrophilic pores. In this review, we mainly summarize recent research data on the viroporin or viroporin-like activity of 2B proteins, which affects the biological function of the membrane, regulates cell death, and affects the host immune response. Considering these mechanisms, the potential application of the 2B protein as a candidate target for antiviral drug development is discussed, along with research challenges and prospects toward realizing a novel treatment strategy for picornavirus infections.


id: cord-004521-25t4s7fr
title: Membrane traffic in the secretory pathway: Take the ’A’ train: on fast tracks to the cell surface
author: Marie, M.
date: 2008-08-26
txt: ./txt/cord-004521-25t4s7fr.txt
cache: ./cache/cord-004521-25t4s7fr.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7079782/
doi: 10.1007/s00018-008-8355-0
summary:
  Typical for this transport is (i) its insensitivity to brefeldin A (BFA), which dissociates selected coat complexes from membranes, resulting in the disassembly of the Golgi apparatus; (ii) its rapid kinetics as compared to the classical secretory pathway; and (iii) its role in the trafficking of lipid raft components. COPII coats function at ER exit sites in the initial export of cargo from the ER [22, 23] , COPI coats operate in forward transport and recycling in the IC and cis-Golgi membranes [24] , while clathrin and associated adaptor proteins (AP1, AP3, AP4, GGA) localize variably to trans-Golgi/TGN and endosomes [25] . However, since different cargo proteins display variable localization in the 20 o C-treated cells, it remained unclear whether they are arrested in a specialized trans-Golgi secretory organelle, or within a complex membrane system located at the crossroads of the exocytic and endocytic pathways [127, 130, 9a] .

abstract:
  Cholesterol, certain lipids, membrane-bound and soluble proteins, as well as viruses that are synthesized in the endoplasmic reticulum (ER), reach the plasma membrane (PM) via non-classical pathway(s) that remain poorly understood. Typical for this transport is (i) its insensitivity to brefeldin A (BFA), which dissociates selected coat complexes from membranes, resulting in the disassembly of the Golgi apparatus; (ii) its rapid kinetics as compared to the classical secretory pathway; and (iii) its role in the trafficking of lipid raft components. Based on results showing that the intermediate compartment (IC) at the ER-Golgi boundary constitutes a stable tubular network that maintains its dynamics in the presence of BFA, we propose that two bidirectional Golgi-bypass pathways to the PM exist, a direct route from early IC elements, and another, reminescent of the yeast secretory pathway, from late IC elements via the endosomal system. These pathways have implications for the organization of the secretory processes in different cell types. (Part of a Multi-author Review)


id: cord-005034-wyipzwo4
title: Targeting of proteins to the Golgi apparatus
author: Gleeson, Paul A.
date: 1994
txt: ./txt/cord-005034-wyipzwo4.txt
cache: ./cache/cord-005034-wyipzwo4.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7088089/
doi: 10.1007/bf00731273
summary:
  These cytoplasmic domain sorting signals mediate interactions with coat structures of budding vesicles and thereby allow the selective vesicular transport of these membrane proteins between a variety of compartments [ 19] . Interestingly, the localization of ERGIC-53 (p53), a type I membrane protein of the intermediate compartment or CGN, requires a KKXX ER retention motif, again suggesting that the CGN may be an extension Overall, the localization signals of non-Golgi proteins are hydrophilic motifs located on either the cytoplasmic or luminal domains of the protein, and some of these signals have been shown to interact specifically with receptor molecules or with protein coats of budding vesicles. A common strategy has been employed by all groups to identify a putative Golgi retention signal(s) by analysing the localization, in transfected mammalian cells, of hybrid molecules containing limited sequences derived from Golgi glycosyltransferases.

abstract:
  The Golgi apparatus maintains a highly organized structure in spite of the intense membrane traffic which flows into and out of this organelle. Resident Golgi proteins must have localization signals to ensure that they are targeted to the correct Golgi compartment and not swept further along the secretory pathway. There are a number of distinct groups of Golgi membrane proteins, including glycosyltransferases, recyclingtrans-Golgi network proteins, peripheral membrane proteins, receptors and viral glycoproteins. Recent studies indicate that there are a number of different Golgi localization signals and mechanisms for retaining proteins to the Golgi apparatus. This review focuses on the current knowledge in this field.


id: cord-007261-b5fgb9wf
author: Murakami, Kazuya
date: 1994-07-17
txt: ./txt/cord-007261-b5fgb9wf.txt
cache: ./cache/cord-007261-b5fgb9wf.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7110061/
doi: 10.1093/oxfordjournals.jbchem.a124489
summary:
  Another chimeric protein construct in which carboxyesterase Sec was connected to the C-terminal region of rat UDP-glucuronosyltransferase (UDP-GT), that contained a double-lysin ER retention motif, was also located in the ER, as determined from the endo H sensitivity and immunofluorescence staining. As a control, other types of fusion proteins were constructed in which the C-terminal portion of UDPglucronosyltransferase, which contains the double-lysine motif for the ER retention, was attached to carboxyesterase Sec. The fusion proteins were expressed in COS cells, and the subcellular localization of the fusion proteins was determined. To determine whether P450s are retained permanently in the ER or recycled between the ER and post-ER compartments through the "export and retrieval" process, we chose a lysosomal enzyme, cathepsin D, as a reporter, which was fused to the N-terminus of P450 at the DNA level and the fusion protein was expressed in COS cells.

title:
  The Transmembrane Region of Microsomal Cytochrome P450 Identified as the Endoplasmic Reticulum Retention Signal(1)

abstract:
  Microsomal-type cytochrome P450s are integral membrane proteins bound to the membrane through their N-terminal transmembrane hydrophobic segment, the signal anchor sequence. To elucidate the determinants that enable the P450s to be located in the ER, we constructed cDNAs encoding chimeric proteins in which a secretory form of carboxyesterase, carboxyesterase Sec, was connected to the N-terminus of the full-length or truncated forms of a microsomal-type P450, P45O(M1), and the constructed plasmids were expressed in COS cells. Since carboxyesterase Sec is an iV-glycosylated secretory protein, endo H treatment could be used to determine whether these chimeric proteins were located in the ER or not. Carboxyesterase Sec with the N-terminal 20 amino acids, containing the transmembrane region, of P46O(M1), was located in the ER, as determined from the endo H sensitivity of the expressed protein and immunofluorescence staining of the cells. As the expressed protein exhibited carboxyesterase activity, it was not retained in the ER through the BiP-dependent quality control system recognizing unfolded proteins. Another chimeric protein construct in which carboxyesterase Sec was connected to the C-terminal region of rat UDP-glucuronosyltransferase (UDP-GT), that contained a double-lysin ER retention motif, was also located in the ER, as determined from the endo H sensitivity and immunofluorescence staining. On the other hand, the sugar moiety of the carboxyesterase Sec connected to the transmembrane segment of UDP-GT, Sec/GTd, was partially resistant to the endo H treatment. From the results of immunofluorescent staining and cell fractiona-tion, it was concluded that the Sec/GTd product was located in the Golgi apparatus. These observations indicated that the N-terminal hydrophobic segment of P45O(M1) is sufficient for the ER membrane retention, whereas the transmembrane segment of UDP-GT is not. To determine whether microsomal P450s are recycled between the ER and Golgi compartments or not, a DNA construct encoding cathepsin D connected to the N-terminus of P45O(M1) was prepared and expressed in COS cells. The fusion protein was phosphorylated, but the phosphorylation was sensitive to alkaline phosphatase. As a control, authentic cathepsin D was subjected to phosphorylation of its oligosaccharide chain that was resistant to the alkaline phosphatase treatment. Since GlcNAc-P-transferase, which forms the alkaline phosphatase-resistant phosphodiester in the sugar chains of lysosome-targeting proteins, is located in the Golgi apparatus, it was concluded that the oligosaccharide chain of the cathepsin D portion of the fusion protein was not phosphorylated, and that the chimeric protein did not go to the Golgi apparatus. These results indicate that P45O(M1) is not recycled from the Golgi compartments to the ER in cells.


id: cord-007353-qg2pb884
title: Polarity of processes with Golgi apparatus in a subpopulation of type I astrocytes
author: Lavi, Ehud
date: 1994-06-06
txt: ./txt/cord-007353-qg2pb884.txt
cache: ./cache/cord-007353-qg2pb884.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7111168/
doi: 10.1016/0006-8993(94)91327-7
summary:
  In order to further investigate which type of astrocytes contain GA in processes we conducted the present study using primary cultures of rat astrocytes and organelle specific antibodies against the GA and the rough endoplasmic reticulum (RER). In a previous ultrastructural, immunocytochemical study from this laboratory, using affinity-purified polyclonal sera specific for the GA, elements of the organelle were detected in peripheral segments of some astrocytic processes in sections of rat brains [68] . Over 95% of the cultured cells stained with the monoclonal antibody against GFAP [43] , an astrocyte specific intermediate filament protein. Staining of MG-160 in processes in rat astrocyte enriched cultures was detected by immunohistochemistry and immunofluorescence with both polyclonal and monoclonal antibodies against MG-160. To confirm that cells which expressed MG-160 in processes were astrocytes, double-labeling immunofluorescence with anti-MG-160 and astrocytic-specific intermediate filament marker (GFAP) antibodies were performed.

abstract:
  The Golgi apparatus-complex (GA), is a key organelle involved in several posttranslational modifications of polypeptides destined for lysosomes, plasma membranes and secretion. As reported from this laboratory, certain astrocytes in rat brain contain cisternae of the GA not only in perikarya, but also in processes. In order to further investigate which type of astrocytes contain GA in processes we conducted the present study using primary cultures of rat astrocytes and organelle specific antibodies against the GA and the rough endoplasmic reticulum (RER). While the perikarya of all cells contained elements of the GA, only a single process of a subset of type I astrocytes, negative to antibodies A2B5 and HNK-1, contained GA. In contrast, elements of the RER were found within perikarya and all processes. In order to confirm that the immunostained structures in processes indeed represent the GA, we exposed cultures to Brefeldin A (BFA), a secretion blocker which disperses the GA and redistributes it to the RER. We observed that BFA disrupted the GA of both perikarya and processes. However, astrocytes were resistant to prolonged incubations with BFA, while a similar treatment killed cultured fibroblasts and PC-12 cells. Furthermore, in astrocytes exposed to BFA for several days, the delicate network of glial fibrillary acidic protein (GFAP), was replaced by large perinuclear masses of the protein. These observations demonstrate that a subset of type I astrocytes have a single process with elements of the GA. We suggest that this specialization of the GA may be related to yet unrecognized secretory or protein processing functions of these cells. The resistance of astrocytes to BFA and the striking changes in their cytoskeleton induced by the drug, may contribute to studies on the mechanism(s) of action of BFA.


id: cord-008590-xivnsldf
author: Tartakoff, Alan M.
date: 2008-04-14
txt: ./txt/cord-008590-xivnsldf.txt
cache: ./cache/cord-008590-xivnsldf.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7133172/
doi: 10.1016/s0074-7696(08)62374-8
summary:
  These cisternae, in conjunction with other associated smoothsurfaced membranes, are responsible for executing net unidirectional intracellular transport (ICT) from the rough endoplasmic reticulum (RER) toward more distally located structures, e.g., lysosomes and the cell surface (24, 35, 40, 47, 85, 1 1 1, 134) . If they do not, given appropriate control experiments, they may be assigned to relatively late sub compartment^.^ The first indications that the site of interruption of ICT by monensin lies only part way across the GC came from study of the progress of N-linked oligosaccharide maturation of Ig (139) ; however, a recent use of monensin should be mentioned since it adds independent support for this idea (37) . The approaches used involved study of the effect of agents which block secretory protein exit from the RER (e.g., uncouplers) (130), correlation between the kinetics of ICT and cleavage, or, best of all, analysis of smooth microsomal or Golgi-enriched subcellular fractions [e.g., of hepatocytes (92, 102) or virally infected cells (68) ].

title:
  The Confined Function Model of the Golgi Complex: Center for Ordered Processing of Biosynthetic Products of the Rough Endoplasmic Reticulum

abstract:
  The organized and characteristic elements of the Golgi complex (GC) are the stacked smooth-surfaced cisternae, which are found in the centrosphere of all eukaryotic cells. These cisternae, in conjunction with other associated smooth-surfaced membranes, are responsible for executing net unidirectional intracellular transport (ICT) from the rough endoplasmic reticulum (RER) toward more distally located structures. This chapter focuses on the broad range of accessory activities that occur during transport, the family of “posttranslational modifications.” These events are, in all likelihood, not essential for the “primary” function of the GC yet they are crucial in allowing the cell to tailor its biosynthetic products for its own needs and the needs of the organism as a whole. In addition to modifying products of the rough endoplasmic reticulum, the GC may be involved in processing events because of its participation in other routes of vesicular traffic—for example, centripetal traffic from the cell surface. Various nonequivalent criteria have been used to ascribe processing events to the GC-autoradiography, preparative or analytic subcellular fractionation, interruption by ICT inhibitors, and delay in the impact of cycloheximide.


id: cord-009371-ub4p4ngr
author: Mollenhauer, Hilton H.
date: 1990-05-07
txt: ./txt/cord-009371-ub4p4ngr.txt
cache: ./cache/cord-009371-ub4p4ngr.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7148783/
doi: 10.1016/0304-4157(90)90008-z
title:
  Alteration of intracellular traffic by monensin; mechanism, specificity and relationship to toxicity

abstract:
  Monensin, a monovalent ion-selective ionophore, facilitates the transmembrane exchange of principally sodium ions for protons. The outer surface of the ionophore-ion comples is composed largely of nonpolar hydrocarbon, which imparts a high solubility to the complexes in nonpolar solvents. In biological systems, these complexes are freely soluble in the lipid components of membranes and, presumably, diffuse or shuttle through the membranes from one aqueous membrane interface to the other. The net effect for monensin is a trans-membrane exchange of sodium ions for protons. However, the interaction of an ionophore with biological membranes, and its ionophoric expression, is highly dependent on the biochemical configuration of the membrane itself. One apparent consequence of this exchange is the neutralization of acidic intracellular compartments such as the trans Golgi apparatus cisternae and associated elements, lysosomes, and certain endosomes. This is accompanied by a disruption of trans Golgi apparatus cisternae and of lysosome and acidic endosome function. At the same time, Golgi apparatus cisternae appear to swell, presumably due to osmotic uptake of water resulting from the inward movement of ions. Monensin effects on Golgi apparatus are observed in cells from a wide range of plant and animal species. The action of monensin is most often exerted on the trans half of the stacked cisternae, often near the point of exit of secretory vesicles at the trans face of the stacked cisternae, or, especially at low monensin concentrations or short exposure times, near the middle of the stacked cisternae. The effects of monensin are quite rapid in both animal and plant cells; i.e., changes in Golgi apparatus may be observed after only 2–5 min of exposure. It is implicit in these observations that the uptake of osmotically active cations is accompanied by a concomitant efflux of H(+) and that a net influx of protons would be required to sustain the ionic exchange long enough to account for the swelling of cisternae observed in electron micrographs. In the Golgi apparatus, late processing events such as terminal glycosylation and proteolytic cleavages are most susceptible to inhibition by monensin. Yet, many incompletely processed molecules may still be secreted via yet poorly understood mechanisms that appear to bypass the Golgi apparatus. In endocytosis, monensin does not prevent internalization. However, intracellular degradation of internalized ligands may be prevented. It is becoming clear that endocytosis involves both acidic and non-acidic compartments and that monensin inhibits those processes that normally occur in acidic compartments. Thus, monensin, which is capable of collapsing Na(+) and H(+) gradients, has gained wide-spread acceptance as a tool for studying Golgi apparatus function and for localizing and identifying the molecular pathways of subcellular vesicular traffic involving acid compartments. Among its advantages are the low concentrations at which inhibitions are produced (0.01–1.0 μM), a minimum of troublesome side effects (e.g., little or no change of protein synthesis or ATP levels) and a reversible action. Because the affinity of monensin for Na(+) is ten times that for K(+), its nearest competitor, monensin mediates primarily a Na(+)-H(+) exchange. Monensin has little tendency to bind calcium. Not only is monensin of importance as an experimental tool, it is of great commercial value as a coccidiostat for poultry and to promote more efficient utilization of feed in cattle. The mechanisms by which monensin interact with coccidia and rumen microflora to achieved these benefits are reasonably well documented. However, the interactions between monensin and the tissues of the host animal are not well understood although the severe toxicological manifestations of monensin poisoning are well known. Equine species are particularly susceptible to monensin poisoning, and a common effect of monensin poisoning is vacuolization and/or swelling of mitochondria in striated muscle. Other pathological injuries to striated muscle, spleen, lung, liver and kidney also have been noted. A consistent observation is cardiac myocyte degeneration as well as vacuolization. Differences in cellular response resulting from exposure to monensin (i.e., Golgi apparatus swelling in cultured cells, isolated tissues, and plants vs.mitochondrial swelling in animals fed monensin) suggest that myocardial damage is due either to a monensin metabolite or is a secondary response to some other derivation. However, as pointed out by Bergen and Bates [26], the underlying mode of action of ionophores is on transmembrane ion fluxes which dissipate cation and proton gradients. Consequently, some or all of the observed monensin effects in vivo in animals could be secondary phenomena caused by disruption of normal membrane physiology resulting from altered ion fluxes.


id: cord-016971-7esuj4ye
title: The Golgi apparatus and main discoveries in the field of intracellular transport
author: Mironov, Alexander A.
date: 2008
txt: ./txt/cord-016971-7esuj4ye.txt
cache: ./cache/cord-016971-7esuj4ye.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7121413/
doi: 10.1007/978-3-211-76310-0_2
summary:
  1964) 1964 GERL concept (Novikoff 1964) 1964 Isolation of Golgi membranes from cells (Morr e and Mollenhauer 1964) 1964 The process of sulphation in the GA (Godman and Lane 1964) 1966 The sugar-nucleotide transport from the cytosol to the Golgi lumen across the Golgi membranes, the role of the GA in glycosylation (Neutra and Leblond 1966) 1966 The origin of lysosomes and the function of clathrin-coated vesicles during protein absorption (Bainton and Farquhar 1966; Friend and Farquhar 1967) 1967 The intracellular transport (Jamieson and Palade 1967a,b) 1969 Galactosyltransferase as a Golgi marker (Whur et al. 1990 ) 1990 The main genes involved in intracellular transport, the genetic evidence in favour of the vesicular model of the transport in yeast (Kaiser and Schekman 1990) 1991 A Golgi retention signal in the membrane-spanning domain (Swift and Machamer 1991) 1993 The role of oligomerization for the retention of Golgi enzymes (Weisz et al.

abstract:
  In this chapter, we summarize important findings in the field of intracellular transport, which have considerably contributed to the understanding of the function and organization of the Golgi apparatus (GA). It is not possible to mention all authors in this huge field. We apologize for gaps and incompleteness, and are thankful for suggestions and corrections.


id: cord-017866-h5ttoo0z
title: Biogenesis of Dense-Core Secretory Granules
author: Bowman, Grant R.
date: 2010-05-27
txt: ./txt/cord-017866-h5ttoo0z.txt
cache: ./cache/cord-017866-h5ttoo0z.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7122546/
doi: 10.1007/978-0-387-93877-6_10
summary:
  For such regulated exocytosis, the vesicles that carry newly-synthesized protein from the TGN accumulate in the cytoplasm until specific extracellular events trigger their fusion with the plasma membrane, resulting in the release of vesicle contents.f The vesicles involved are called dense-core granules (DCGs), the name reflecting the fact that the contents are so highly condensed that they form a large electron-dense plug in the vesicle lumen. In support of this hypothesis, recent studies have suggested that prohormone convertases 1 and 2, which are responsible for proteolytic cleavageof lumenal proteins during granule maturation, are sorted to ISGs by virtue of C-terminal membrane raft-associated tails, which are by themselves necessary and sufficient for targeting to DCGs,uo 120 Additionally, cytoplasmic signals on some transmembrane proteins appear to play important roles in sorting, but the mechanisms are unknown.

abstract:
  Dense core granules (DCGs) are vesicular organelles derived from outbound traffic through the eukaryotic secretory pathway. As DCGs are formed, the secretory pathway can also give rise to other types of vesicles, such as those bound for endosomes, lysosomes, and the cell surface. DCGs differ from these other vesicular carriers in both content and function, storing highly concentrated cores’ of condensed cargo in vesicles that are stably maintained within the cell until a specific extracellular stimulus causes their fusion with the plasma membrane. These unique features are imparted by the activities of membrane and lumenal proteins that are specifically delivered to the vesicles during synthesis. This chapter will describe the DCG biogenesis pathway, beginning with the sorting of DCG proteins from proteins that are destined for other types of vesicle carriers. In the trans-Golgi network (TGN), sorting occurs as DCG proteins aggregate, causing physical separation from non-DCG proteins. Recent work addresses the nature of interactions that produce these aggregates, as well as potentially important interactions with membranes and membrane proteins. DCG proteins are released from the TGN in vesicles called immature secretory granules (ISGs). The mechanism of ISG formation is largely unclear but is not believed to rely on the assembly of vesicle coats like those observed in other secretory pathways. The required cytosolic factors are now beginning to be identified using in vitro systems with purified cellular components. ISG transformation into a mature fusion-competent, stimulus-dependent DCG occurs as endoproteolytic processing of many DCG proteins causes continued condensation of the lumenal contents. At the same time, proteins that fail to be incorporated into the condensing core are removed by a coat-mediated budding mechanism, which also serves to remove excess membrane and membrane proteins from the maturing vesicle. This chapter will summarize the work leading to our current view of granule synthesis, and will discuss questions that need to be addressed in order to gain a more complete understanding of the pathway.


id: cord-018572-e2qq4ngq
author: Jackson, Catherine L.
date: 2014-05-22
txt: ./txt/cord-018572-e2qq4ngq.txt
cache: ./cache/cord-018572-e2qq4ngq.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7123483/
doi: 10.1007/978-3-319-07761-1_8
summary:
  This feature is conserved in modern organisms, for example, in humans, which have only 5 Arf proteins, yet at least 15 GEFs and 31 GAPs. Perhaps a clue as to the Arf4 TGN VxPx targeting motif AP adaptor protein, BAR Bin/Amphiphysin/Rvs, CC coiled-coil, COP coatomer protein, ER endoplasmic reticulum, ERGIC ER-Golgi intermediate compartment, GAT GGA (Golgi-localized, γ-adaptin homologous, ADP-ribosylation factor-binding protein) and TOM1 homologous, GRAB GRIP (golgin-97/RabBP2α/Imh1p/p230)-related Arf binding, PM plasma membrane, TGN trans-Golgi network; ND, not determined nature of the primordial Arf protein comes from the protozoan parasite Trypanosoma brucei, which expresses a single Arf protein that has characteristics of both Class I and Class III mammalian Arfs. How a single Arf protein can recruit multiple coats to different membrane sites in cells is still not fully understood, but one important contribution to specificity comes from the Arf GEFs. In both mammalian and yeast cells, GBF1 and Gea1/2, respectively, interact directly with COPI (Deng et al.

title:
  Arf Proteins and Their Regulators: At the Interface Between Membrane Lipids and the Protein Trafficking Machinery

abstract:
  The Arf small GTP-binding (G) proteins regulate membrane traffic and organelle structure in eukaryotic cells through a regulated cycle of GTP binding and hydrolysis. The first function identified for Arf proteins was recruitment of cytosolic coat complexes to membranes to mediate vesicle formation. However, subsequent studies have uncovered additional functions, including roles in plasma membrane signalling pathways, cytoskeleton regulation, lipid droplet function, and non-vesicular lipid transport. In contrast to other families of G proteins, there are only a few Arf proteins in each organism, yet they function specifically at many different cellular locations. Part of this specificity is achieved by formation of complexes with their guanine nucleotide-exchange factors (GEFs) and GTPase activating proteins (GAPs) that catalyse GTP binding and hydrolysis, respectively. Because these regulators outnumber their Arf substrates by at least 3-to-1, an important aspect of understanding Arf function is elucidating the mechanisms by which a single Arf protein is incorporated into different GEF, GAP, and effector complexes. New insights into these mechanisms have come from recent studies showing GEF–effector interactions, Arf activation cascades, and positive feedback loops. A unifying theme in the function of Arf proteins, carried out in conjunction with their regulators and effectors, is sensing and modulating the properties of the lipids that make up cellular membranes.


id: cord-020788-a33vcapl
title: Signals and Mechanisms of Sorting in Epithelial Polarity
author: Gottardi, Cara J.
date: 2008-05-22
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7147917/
doi: 10.1016/s1569-2558(08)60020-x
abstract:
  This chapter discusses epithelial-membrane polarity, sorting pathways in polarized cells, and the sorting-signal paradigm. Polarized epithelial cells have long captured the attention of cell biologists and cell physiologists. At the electron-microscopic level, one of the most apparent and fundamental features of this cell type is its polarized organization of intracellular organelles and its structurally and compositionally distinct lumenal (apical) and serosal (basolateral) plasma-membrane domains. The polarized epithelial phenotype is an absolute necessity for organ-system function. In the most general sense, these cells organize to form a continuous, single layer of cells, or epithelium, which serves as a semi-permeable barrier between apposing and biologically distinct compartments. Within the tubules of the nephron, these cells orchestrate complex ion-transporting processes that ultimately control the overall fluid balance of the organism. At the surface of the gastrointestinal tract, specialized versions of this cell type control the digestion, absorption, and immuno-protection of the organism.


id: cord-022313-2675sjlf
title: The Use of Glycosylation Inhibitors to Study Glycoconjugate Function
author: Elbein, Alan D.
date: 2012-12-02
txt: ./txt/cord-022313-2675sjlf.txt
cache: ./cache/cord-022313-2675sjlf.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155559/
doi: 10.1016/b978-0-12-589630-6.50009-5
abstract: nan
summary:
  Perhaps one control for some of these studies would be to use other inhibitors (i.e., cycloheximide or puromycin) that are known to block protein synthesis but do not affect carbohydrate synthesis or addition, or some other inhibitors that mod ify the structure of the carbohydrate chain, and compare the effects of these compounds with those of tunicamycin on the function of the particular glycoprotein. When various cultured animal cells are grown or incubated in the presence of this alkaloid, the processing of N-linked glycoproteins is blocked at the first step in the pathway (see Fig. 3 ), and the asparaginelinked glycoproteins have oligosaccharides mostly of the Glc 3 Man 7 _ 9 (GlcNAc) 2 structure. The sugar analog, 2-fluoro-2-deoxyglucose, which was previously shown to inhibit dolichyl-P-mannose formation and lipid-linked oligosaccha rides (154) , also altered the synthesis of the GPI-anchored protein alka line phosphatase in JEG-3 cells and caused the accumulation of a proform of the enzyme.


id: cord-022499-7d58f1k3
title: Transmembrane α helices
author: Mall, Sanjay
date: 2004-01-07
txt: ./txt/cord-022499-7d58f1k3.txt
cache: ./cache/cord-022499-7d58f1k3.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7157917/
doi: 10.1016/s1063-5823(02)52014-7
summary:
  For example, if effects were averaged over three shells of lipids, changes in fatty acyl chain lengths by 4 and 10 carbons from that giving optimal interaction would decrease lipid-protein binding constants by factors of 1.6 and 21, respectively. These results suggest that the effects of charge on the interactions between phospholipids and transmembrane ot helices will often be rather small and will be strongly dependent on the detailed structure of the peptide and its orientation in the membrane. However, there is evidence for the presence of a small number of "special" anionic phospholipids binding to some membrane proteins, acting as "cofactors." An example is provided by cytochrome c oxidase, whose crystal structure shows the presence of a lipid molecule bound between the transmembrane a helices (Iwata et al., 1995) . It could therefore be that matching of the thickness of the lipid bilayer and the transmembrane length of the protein is important in retention in ER, as was suggested for the Golgi complex.

abstract:
  This chapter discusses effects of intrinsic membrane proteins on lipid bilayers and model transmembrane α helices. Incorporation of a protein into a lipid bilayer has significant effects on the properties of the bilayer. The rough surface presented by a protein to the surrounding lipid bilayer tends to produce poor packing unless the lipid fatty acyl chains distort to match the surface of the protein. In a liquid crystalline bilayer the lipid fatty acyl chains are disordered, because the chains undergo extensive wobbling fluctuations. The presence of a rigid protein surface reduces the extent of these motional fluctuations. However, the chains tilt and become conformationally disordered to maximize contact with the rough surface of the protein. The net result is that the presence of a protein leads to decreased order for the chains, with a wide range of chain orientations relative to the bilayer normal, but with reduced extent and rate of motion. Because of the reduced motion, lipids adjacent to membrane proteins are often referred to as being motionally restricted. It is clear that the reasons for the disorder of the bulk lipids and the disorder of the lipids adjacent to the protein are different; for the bulk phospholipids, the disorder is dynamic, whereas, for the boundary lipids the disorder is static.


id: cord-022774-wasdp2gh
author: Morré, D. James
date: 2012-02-07
txt: ./txt/cord-022774-wasdp2gh.txt
cache: ./cache/cord-022774-wasdp2gh.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7161763/
doi: 10.1111/j.1768-322x.1989.tb03009.x
summary:
  The findings show parallel responses between the temperature dependency of transition vesicle formation in vitro and in situ and suggest that a subpopulation of the transitional endoplasmic reticulum may be morphologically and functionally homologous to the 16°C compartment observed in virally‐infected cell lines grown at low temperatures. Studies were then conducted with isolated transitional endoplasmic reticulum fractions from rat liver to determine if a similar mechanism of control by temperature of transition vesicle formation could be duplicated in the cell-free system. With further increases in temperature, the numbers of transition vesicles appeared to be increased slightly but the tubular elements of the endoplasmic reticulum did not reappear within the Golgi apparatus zone. Numbers of transition vesicles were approximately doubled relative to the control preparations and the peripheral cytoplasm contained numerous tubular transition elements of the endoplasmic reticulum similar in appearance to those observed with incubation at 16°C (Fig. 7A) .

title:
  Identification of the 16°C compartment of the endoplasmic reticulum in rat liver and cultured hamster kidney cells

abstract:
  Summary— In many systems transfer between the endoplasmic reticulum and the Golgi apparatus is blocked at temperatures below 16°C. In virus‐infected cells in culture, a special membrane compartment is seen to accumulate. Our studies with rat liver show a similar response to temperature both in situ with slices and in vitro with isolated transitional endoplasmic relticulum fractions. With isolated transitional endoplasmic reticulum fractions, when incubated in the presence of nucleoside triphosphate and a cytosol fraction, temperature dependent formation of vesicles occurred with a Q(10) of −2 but was apparent only at temperatures greater than 12°C. A similar response was seen in situ at 12°C and 16°C where fusion of transition vesicles with cis Golgi apparatus, but not their formation, was blocked and transition vesicles accumulated in large numbers. At 18°C and below and especially at 8°C and 12°C, the cells responded by accumulating smooth tubular transitional membranes near the cis Golgi apparatus face. With cells and tissue slices at 20°C neither transition vesicles nor the smooth tubular elements accumulated. Those transition vesicles which formed at 37°C were of a greater diameter than those formed at 4°C both in situ and in vitro. The findings show parallel responses between the temperature dependency of transition vesicle formation in vitro and in situ and suggest that a subpopulation of the transitional endoplasmic reticulum may be morphologically and functionally homologous to the 16°C compartment observed in virally‐infected cell lines grown at low temperatures.


id: cord-026010-61j07gq3
title: Alkaloid Glycosidase Inhibitors
author: Elbein, Alan D.
date: 2010-06-03
txt: ./txt/cord-026010-61j07gq3.txt
cache: ./cache/cord-026010-61j07gq3.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7271188/
doi: 10.1016/b978-0-08-091283-7.00098-9
abstract: nan
summary:
  or b!mannosidase but instead proved to be an e}ective inhibitor of a!glucosidase\ with a level of activity only slightly less than that of castanospermine[ 21 Numerous additional examples of inhibitory speci_cities due to both naturally occurring alkaloids and synthetic analogues have further undermined this empirical approach and it is obvious that structureÐactivity correlations can only be developed with the aid of sophisticated molecular modeling techniques[ Molecular orbital calculations and molecular modeling have been applied to a series of known mannosidase inhibitors and others which were expected to inhibit but failed to do so[ The results showed that good inhibitors _t closely with a single low!energy conformer of the mannosyl cation and demonstrated that 5!epi!castanospermine did not comply with the structural requirements[ 65\66 The electronegative binding groups present in the inhibitor necessary for speci_city and activity were established\ as were those which were of little signi_cance[ Additional studies of this type should provide valuable information regarding the receptor sites on the various enzymes but the inhibition data available is compromised by the variability in enzymes and the conditions under which measurements have been made[ A comprehensive screening program using standardized conditions would provide much more useful information for structureÐactivity correlations and consequently the design of speci_c and potent inhibitors[


id: cord-102964-zh737cjk
title: Modulation of endothelial organelle size as an antithrombotic strategy
author: Ferraro, Francesco
date: 2020-05-17
txt: ./txt/cord-102964-zh737cjk.txt
cache: ./cache/cord-102964-zh737cjk.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1101/2020.05.16.099580
doi: 10.1101/2020.05.16.099580
summary:
  Out of 1280 human licensed drugs we found 58 compounds fitting our criteria, with a variety of mechanisms of action consistent suggesting a number of pathways that influence biogenesis of WPBs. A quantitative high-throughput microscopy-based workflow, dubbed highthroughput morphometry (HTM), allows rapid quantification of the size of tens to hundreds of thousands of WPBs within thousands of endothelial cells (Ferraro et al., 2014) . We have previously shown that treatment of endothelial cells with two statins, simvastatin and fluvastatin, induces WPB size shortening, resulting in reduced adhesive properties of the VWF released by activated endothelial cells (HUVEC), measured by the reduced size of platelet-decorated VWF strings and by the recruitment of VWF from a flowing plasma pool (Ferraro et al., 2016) . Further to the potential toxicity associated with administration of drugs at high concentrations, we note that in vitro combination of WPB-size reducing treatments, acting through different mechanisms, can display synergy in the abatement of plasma VWF recruitment to the endothelial surface (Supplemental Figure 1) .

abstract:
  It is long-established that Von Willebrand Factor (VWF) is central to haemostasis and thrombosis. Endothelial VWF is stored in cell-specific secretory granules, Weibel-Palade bodies (WPBs), uniquely rod-like exocytic organelles generated in a wide range of lengths (0.5 to 5.0 µm). It has been shown that WPB size responds to physiological cues and pharmacological treatment and that, under flow, VWF secretion from shortened WPBs produces a dramatic reduction of platelet and plasma VWF adhesion to an endothelial surface. WPB-shortening therefore represents a novel target for antithrombotic therapy acting via modulation of VWF adhesive activity. To this aim, we screened a library of licenced drugs and identified several that prompt WPB size reduction. These compounds therefore constitute a novel set of potentially antithrombotic compounds. Summary The size of the endothelial secretory granules that store Von Willebrand Factor correlates with its activity, central to haemostasis and thrombosis. Here, human-licenced drugs that reduce the size of these secretory granules are identified, providing a set of novel potential anti-thrombotic compounds.


id: cord-104223-ht3ry9i0
title: Sorting within the regulated secretory pathway occurs in the trans- Golgi network
author: nan
date: 1990-01-01
txt: ./txt/cord-104223-ht3ry9i0.txt
cache: ./cache/cord-104223-ht3ry9i0.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2115992/
doi: nan
summary:
  Bioactive peptides cleaved from the egg-laying hormone precursor in the bag cell neurons of Aplysia are sorted into distinct dense core vesicle classes (DCVs). All other changes were minor in comparison, and in the compartments important in these studies-small and large immature vesicles, clear vesicles, and Golgi apparatus-the results between calculations at three HD values differ by no more than 5 % in any experiment. Both amino and carboxy terminal-associated radioactivity are transported through the Golgi stacks and enter small immature DCVs (defined by membrane extensions, connection to tubules, or nonspherical morphology) and clear vesicles after a 30-min pulse and 30-min chase (Fig. 4 B, Fig. 5 , and Table I ). After the initial cleavage event, the ELH-containing carboxy-terminal intermediate condenses in one region of the TGN (small immature vesicles) and the amino-terminal bag cell peptide-containing intermediate condenses in another region of the TGN (large immature vesicles).

abstract:
  Bioactive peptides cleaved from the egg-laying hormone precursor in the bag cell neurons of Aplysia are sorted into distinct dense core vesicle classes (DCVs). Bag cell prohormone processing can be divided into two stages, an initial cleavage occurring in a late Golgi compartment, which is not blocked by monensin, and later cleavages that occur within DCVs and are blocked by monensin. Prohormone intermediates are sorted in the trans-Golgi network. The large soma-specific DCVs turn over, while the small DCVs are transported to processes for regulated release. Thus, protein trafficking differentially regulates the levels and localization of multiple biologically active peptides derived from a common prohormone.


id: cord-104231-fi8pskod
author: nan
date: 1994-04-02
txt: ./txt/cord-104231-fi8pskod.txt
cache: ./cache/cord-104231-fi8pskod.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2120028/
doi: nan
summary:
  Unlike CD8-C (see Fig. 3 C) , the CD8-AC hybrid protein was not in the Golgi apparatus but exhibited a cell surface staining pattern and additional accumulation in intracel* The two categories of transfected cells, low "expressers" (<) and high "expressers ~ (>), were defined as described in Materials and Methods. At higher levels of expression (>60 gold particles/cell section) the percentage of labeling over the Golgi apparatus fell (to 60 5:7 %) and rose over endosomes (to 29 5:7 %) and the plasma membrane (to 11 + 7%) ( Table I) . At higher levels of expression (>50 gold particles/cell section) the percentage of total labeling over the Golgi apparatus fell (to 61 5: 8%) and rose over endosomes (to 35 + 8%) and plasma membrane (to 4 + 3%) ( Table I) .

title:
  The TGN38 glycoprotein contains two non-overlapping signals that mediate localization to the trans-Golgi network

abstract:
  The membrane-spanning and cytoplasmic domains of CD4 and CD8 were replaced by those of TGN38. After transient expression in HeLa cells, the location of the hybrid proteins was determined using immunofluorescence and quantitative immuno-electron microscopy, FACS analysis and metabolic labeling. The membrane-spanning domain was found to contain a signal that localized hybrid proteins to the TGN. This was in addition to the signal previously identified in the cytoplasmic domain (Bos, K., C. Wraight, and K. Stanley. 1993. EMBO (Eur. Mol. Biol. Organ) J. 12:2219-2228. Humphrey, J. S., P. J. Peters, L. C. Yuan, and J. S. Bonifacino. 1993. J. Cell Biol. 120:1123-1135. Wong, S. H., and W. Hong. 1993. J. Biol. Chem. 268:22853-22862). The different properties of these two signals suggest that each operates by a different mechanism.


id: cord-104239-xxlcdbqi
title: The organization of endoplasmic reticulum export complexes
author: nan
date: 1996-10-01
txt: ./txt/cord-104239-xxlcdbqi.txt
cache: ./cache/cord-104239-xxlcdbqi.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2121027/
doi: nan
summary:
  While the formation of ER to Golgi carrier vesicles in secretory tissues is largely confined to the transitional region facing the juxtanuclear Golgi apparatus (Palade, 1975) , studies in other cell lines have shown that export from the ER can originate from multiple sites that appear randomly distributed throughout the cytoplasm and, in most instances, distant from the Golgi complex. The local density of buds on individual cisternae associated with export complexes was determined as follows: using a stack of sequential serial sections, we followed one continuous bud-bearing zone of ER membrane that contained at least four buds. In the presence of the Sarl mutant, VSV-G reached a density of 700 _+ 200 gold particles per ~m 2 in a planar projection of the cluster (Fig. 10 E) , reinforcing our previous observations that the budding activity associated with export complexes involves concentration.

abstract:
  Export of cargo from the ER occurs through the formation of 60-70nm COPII-coated vesicular carriers. We have applied serial-thin sectioning and stereology to quantitatively characterize the three-dimensional organization of ER export sites in vivo and in vitro. We find that ER buds in vivo are nonrandomly distributed, being concentrated in regional foci we refer to as export complexes. The basic organization of an export complex can be divided into an active COPII-containing budding zone on a single ER cisterna, which is adjacent to budding zones found on distantly connected ER cisternae. These budding foci surround and face a central cluster of morphologically independent vesicular-tubular elements that contain COPI coats involved in retrograde transport. Vesicles within these export complexes contain concentrated cargo molecules. The structure of vesicular-tubular clusters in export complexes is particularly striking in replicas generated using a quick-freeze, deep-etch approach to visualize for the first time their three-dimensional organization and cargo composition. We conclude that budding from the ER through recruitment of COPII is confined to highly specialized export complexes that topologically restrict anterograde transport to regional foci to facilitate efficient coupling to retrograde recycling by COPI.


id: cord-104241-cqvnxsbo
author: Bryant, Nia J.
date: 1997-01-27
txt: ./txt/cord-104241-cqvnxsbo.txt
cache: ./cache/cord-104241-cqvnxsbo.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2134822/
doi: nan
summary:
  The yeast TGN is defined as the compartment where proteins destined for the cell surface are sorted from those destined for delivery to the vacuole, and contains the three processing proteinases involved in the maturation of the mating pheromone ␣ -factor (Kex2p, Kex1p, and Ste13p; also called dipeptidyl aminopeptidase A [DPAP A] 1 ; Bryant and Boyd, 1993; Nothwehr et al., 1993) , as well as the vacuolar protein sorting receptor (Vps10p; Marcusson et al., 1994; Cereghino et al., 1995; Cooper and Stevens, 1996) . By contrast, (⌬68-106)A-ALP behaved just like (F/A)A-ALP in that it localized to vacuolar membranes (Nothwehr et al., 1993; our unpublished results) and was processed with halftimes of ‫56-06ف‬ min in both wild-type and vps27 mutant cells ( Fig. 8 and Table III) presumably since it contains information to slow exit from the TGN.

title:
  Two Separate Signals Act Independently to Localize a Yeast Late Golgi Membrane Protein through a Combination of Retrieval and Retention

abstract:
  The localization of proteins to late-Golgi membranes (TGN) of Saccharomyces cerevisiae is conferred by targeting motifs containing aromatic residues in the cytosolic domains of these proteins. These signals could act by directing retrieval from a post-Golgi compartment or by preventing exit from the TGN. To investigate the mechanism of localization of yeast TGN proteins, we used the heterologous protein A-ALP (consisting of the cytosolic domain of dipeptidyl aminopeptidase A [DPAP A] fused to the transmembrane and luminal domains of the vacuolar protein alkaline phosphatase [ALP]), which localizes to the yeast TGN. Insertion of the aromatic residue–based TGN localization motif (FXFXD) of DPAP A into the cytosolic domain of ALP results in a protein that resides in the TGN. We demonstrate that the FXFXD motif confers Golgi localization through retrieval from a post-Golgi compartment by detecting a post-Golgi processed form of this protein in the TGN. We present an assay that uncouples retrieval-mediated Golgi localization from static retention-based localization, allowing measurement of the rate at which proteins exit the yeast TGN. We also demonstrate that the cytosolic domain of DPAP A contains additional information, separate from the retrieval motif, that slows exit from the TGN. We propose a model for DPAP A localization that involves two distinct mechanisms: one in which the FXFXD motif directs retrieval from a post-Golgi compartment, and a second that slows the rate at which DPAP A exits the TGN.


id: cord-104268-q1jx0n0l
author: nan
date: 1995-11-02
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2200012/
doi: nan
title:
  Localization and targeting of the Saccharomyces cerevisiae Kre2p/Mnt1p alpha 1,2-mannosyltransferase to a medial-Golgi compartment

abstract:
  The yeast Kre2p/Mnt1p alpha 1,2-mannosyltransferase is a type II membrane protein with a short cytoplasmic amino terminus, a membrane- spanning region, and a large catalytic luminal domain containing one N- glycosylation site. Anti-Kre2p/Mnt1p antibodies identify a 60-kD integral membrane protein that is progressively N-glycosylated in an MNN1-dependent manner. Kre2p/Mnt1p is localized in a Golgi compartment that overlaps with that containing the medial-Golgi mannosyltransferase Mnn1p, and distinct from that including the late Golgi protein Kex1p. To determine which regions of Kre2p/Mnt1p are required for Golgi localization, Kre2p/Mnt1p mutant proteins were assembled by substitution of Kre2p domains with equivalent sequences from the vacuolar proteins DPAP B and Pho8p. Chimeric proteins were tested for correct topology, in vitro and in vivo activity, and were localized intracellularly by indirect immunofluorescence. The results demonstrate that the NH2-terminal cytoplasmic domain is necessary for correct Kre2p Golgi localization whereas, the membrane-spanning and stem domains are dispensable. However, in a test of targeting sufficiency, the presence of the entire Kre2p cytoplasmic tail, plus the transmembrane domain and a 36-amino acid residue luminal stem region was required to localize a Pho8p reporter protein to the yeast Golgi.


id: cord-104269-9r7rqqqk
author: nan
date: 1994-07-02
txt: ./txt/cord-104269-9r7rqqqk.txt
cache: ./cache/cord-104269-9r7rqqqk.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2200027/
doi: nan
summary:
  title: Sorting signals in the MHC class II invariant chain cytoplasmic tail and transmembrane region determine trafficking to an endocytic processing compartment Ii-TR chimera containing the Ii cytoplasmic tail and transmembrane region is delivered directly to the endocytic pathway by an intracellular route, implying that the Ii sorting signals are efficiently recognized by sorting machinery located in the trans-Golgi. Ii-TR chimera containing the Ii cytoplasmic tail and transmembrane region is delivered directly to the endocytic pathway by an intracellular route, implying that the Ii sorting signals are efficiently recognized by sorting machinery located in the trans-Golgi. Further, the rate of synthesis of the Iicx and Iicr+m chimeras was 4-and 8-fold higher, respectively, than that of wild-type TR even though the chimeric receptors were expressed in lower amounts on the cell surface suggesting most of the chimeric molecules were trafficking by a direct intracellular route to the endocytic compartment where they were degraded.

title:
  Sorting signals in the MHC class II invariant chain cytoplasmic tail and transmembrane region determine trafficking to an endocytic processing compartment

abstract:
  Targeting of MHC class II molecules to the endocytic compartment where they encounter processed antigen is determined by the invariant chain (Ii). By analysis of Ii-transferrin receptor (TR) chimera trafficking, we have identified sorting signals in the Ii cytoplasmic tail and transmembrane region that mediate this process. Two non-tyrosine-based sorting signals in the Ii cytoplasmic tail were identified that mediate localization to plasma membrane clathrin-coated pits and promote rapid endocytosis. Leu7 and Ile8 were required for the activity of the signal most distal to the cell membrane whereas Pro15 Met16 Leu17 were important for the membrane-proximal signal. The same or overlapping non- tyrosine-based sorting signals are essential for delivery of Ii-TR chimeras, either by an intracellular route or via the plasma membrane, to an endocytic compartment where they are rapidly degraded. The Ii transmembrane region is also required for efficient delivery to this endocytic processing compartment and contains a signal distinct from the Ii cytoplasmic tail. More than 80% of the Ii-TR chimera containing the Ii cytoplasmic tail and transmembrane region is delivered directly to the endocytic pathway by an intracellular route, implying that the Ii sorting signals are efficiently recognized by sorting machinery located in the trans-Golgi.


id: cord-104279-choywmwd
author: nan
date: 1992-10-01
txt: ./txt/cord-104279-choywmwd.txt
cache: ./cache/cord-104279-choywmwd.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2289628/
doi: nan
summary:
  First, to determine if the lumenal domain was sorted to the vacuole when expressed in the secretory pathway as a soluble protein, a gene fusion was used to create the protein ctFss-B, consisting of the NH2-terminal ER-targeting signal sequence of prepro-t~ factor fused to the lumenal domain of DPAP B at residue 49 ( Fig. 1 B) . To ad-dress the possibility that the mutant constructs analyzed in this study were mislocalized to the plasma membrane followed by rapid endocytic uptake to the vacuole, indirect immunofluorescence experiments were performed on BB-Inv, B-A-B, A20-BB, and/x22-AA-B expressed in a secl strain at 34~ As a positive control for accumulation in secretory vesicles, the localization of the fusion protein Fusl-LacZp was analyzed (Trueheart et al., 1987) .

title:
  Membrane protein sorting in the yeast secretory pathway: evidence that the vacuole may be the default compartment

abstract:
  The targeting signals of two yeast integral membrane dipeptidyl aminopeptidases (DPAPs), DPAP B and DPAP A, which reside in the vacuole and the Golgi apparatus, respectively, were analyzed. No single domain of DPAP B is required for delivery to the vacuolar membrane, because removal or replacement of either the cytoplasmic, transmembrane, or lumenal domain did not affect the protein's transport to the vacuole. DPAP A was localized by indirect immunofluorescence to non-vacuolar, punctate structures characteristic of the yeast Golgi apparatus. The 118-amino acid cytoplasmic domain of DPAP A is sufficient for retention of the protein in these structures, since replacement of the cytoplasmic domain of DPAP B with that of DPAP A resulted in an immunolocalization pattern indistinguishable from that of wild type DPAP A. Overproduction of DPAP A resulted in its mislocalization to the vacuole, because cells expressing high levels of DPAP A exhibited vacuolar as well as Golgi staining. Deletion of 22 residues of the DPAP A cytoplasmic domain resulted in mislocalization of the mutant protein to the vacuole. Thus, the cytoplasmic domain of DPAP A is both necessary and sufficient for Golgi retention, and removal of the retention signal, or saturation of the retention apparatus by overproducing DPAP A, resulted in transport to the vacuole. Like wild type DPAP B, the delivery of mutant membrane proteins to the vacuole was unaffected in the secretory vesicle-blocked sec1 mutant; thus, transport to the vacuole was not via the plasma membrane followed by endocytosis. These data are consistent with a model in which membrane proteins are delivered to the vacuole along a default pathway.


id: cord-253466-7gpije5d
author: Netherton, Christopher
date: 2007-08-31
txt: ./txt/cord-253466-7gpije5d.txt
cache: ./cache/cord-253466-7gpije5d.txt
extension: .txt
mime: text/plain
url: https://www.sciencedirect.com/science/article/pii/S0065352707700040
doi: 10.1016/s0065-3527(07)70004-0
summary:
  Significantly, Poliovirus infection causes enrichment of GEFs in membranes containing replicase proteins, and this would provide a mechanism for increasing levels of Arf1-GTP at sites of virus replication. There is evidence that Tobacco mosaic virus also uses the ER as a site of replication because the replicase enzyme and viral RNA are located on the ER of infected cells, and infection causes major changes in ER morphology (Reichel and Beachy, 1998) , including ER aggregation and formation of lamella structures. Even though these viruses infect a diverse range of hosts from different phyla, including vertebrates [poxviruses, African swine fever virus (ASFV)], arthropods (entomopox, ASFV, chloriridoviruses), amphibians and fish (Ranavirus, Megalocytivirus, and Lymphocystivirus genera of the Iridoviridae family), marine algae (phycodnaviruses), and protozoa (mimivirus), they all generate cytoplasmic factories as major sites of virus assembly and replication (illustrated in Fig. 4 ). Formation of DNA replication structures in herpes virus-infected cells requires a viral DNA binding protein

title:
  A Guide to Viral Inclusions, Membrane Rearrangements, Factories, and Viroplasm Produced During Virus Replication

abstract:
  Virus replication can cause extensive rearrangement of host cell cytoskeletal and membrane compartments leading to the “cytopathic effect” that has been the hallmark of virus infection in tissue culture for many years. Recent studies are beginning to redefine these signs of viral infection in terms of specific effects of viruses on cellular processes. In this chapter, these concepts have been illustrated by describing the replication sites produced by many different viruses. In many cases, the cellular rearrangements caused during virus infection lead to the construction of sophisticated platforms in the cell that concentrate replicase proteins, virus genomes, and host proteins required for replication, and thereby increase the efficiency of replication. Interestingly, these same structures, called virus factories, virus inclusions, or virosomes, can recruit host components that are associated with cellular defences against infection and cell stress. It is possible that cellular defence pathways can be subverted by viruses to generate sites of replication. The recruitment of cellular membranes and cytoskeleton to generate virus replication sites can also benefit viruses in other ways. Disruption of cellular membranes can, for example, slow the transport of immunomodulatory proteins to the surface of infected cells and protect against innate and acquired immune responses, and rearrangements to cytoskeleton can facilitate virus release.


id: cord-255027-xsuialnn
title: Glycosyltransferase complexes in eukaryotes: long-known, prevalent but still unrecognized
author: Kellokumpu, Sakari
date: 2015-10-17
txt: ./txt/cord-255027-xsuialnn.txt
cache: ./cache/cord-255027-xsuialnn.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/26474840/
doi: 10.1007/s00018-015-2066-0
summary:
  One of the first examples of these was the observation that a soluble lactose synthase (LS, EC 2.4.1.22, for enzyme names and definitions, see Table 1 ) typically found in bovine milk consists of two The term ''''complex'''' is used in this review to define a functional assembly of two or more similar (homomer) or dissimilar (heteromer) glycosyltransferases that interact with each other and in the case of the latter, typically act sequentially during glycan synthesis. Yeast N-glycosyltransferase complexes The yeast N-glycosylation pathway shows a high degree of pathway conservation with higher eukaryotes, involving similar oligosaccharide-dolichol precursor synthesis, glycan transfer to nascent proteins by an oligosaccharyltransferase (OST) complex, and removal in the endoplasmic reticulum (ER) of the three glucoses and the central-arm a1,2-linked Man from the newly transferred Glc 3 Man 9 GlcNAc 2 [1, 2, [13] [14] [15] .

abstract:
  Glycosylation is the most common and complex cellular modification of proteins and lipids. It is critical for multicellular life and its abrogation often leads to a devastating disease. Yet, the underlying mechanistic details of glycosylation in both health and disease remain unclear. Partly, this is due to the complexity and dynamicity of glycan modifications, and the fact that not all the players are taken into account. Since late 1960s, a vast number of studies have demonstrated that glycosyltransferases typically form homomeric and heteromeric complexes with each other in yeast, plant and animal cells. To propagate their acceptance, we will summarize here accumulated data for their prevalence and potential functional importance for glycosylation focusing mainly on their mutual interactions, the protein domains mediating these interactions, and enzymatic activity changes that occur upon complex formation. Finally, we will highlight the few existing 3D structures of these enzyme complexes to pinpoint their individual nature and to emphasize that their lack is the main obstacle for more detailed understanding of how these enzyme complexes interact and function in a eukaryotic cell.


id: cord-255981-3zvwu5bd
author: Bui, Quynh Trang
date: 2009-08-11
txt: ./txt/cord-255981-3zvwu5bd.txt
cache: ./cache/cord-255981-3zvwu5bd.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/19669794/
doi: 10.1007/s00438-009-0473-3
summary:
  The majority of these Arf1 GEFs are high molecular weight proteins, on the order of 200 kDa, and for this reason they have been referred to as the large Arf GEFs. The GBF/Gea and BIG/ Sec7 Arf1 GEFs function in internal membrane systems such as the Golgi apparatus, the trans-Golgi network (TGN) and endosomal pathways (Zhao et al. In this review, we will discuss the evolution of these Arf1 GEFs, and present an analysis of conserved domains that are common to both subfamilies as well as those that are speciWc to either the GBF/Gea or BIG/Sec7 proteins. As described previously, the large Arf1 GEFs have Wve major sequence homology domains that are common to members of both the GBF/Gea and the BIG/Sec7 subfamilies (Mouratou et al. The highly conserved sequence homology domains of the GBF/Gea and the BIG/Sec7 Arf1 GEFs suggest that they have important, conserved functions in evolution, and are likely to be involved in protein-protein interactions.

title:
  Large Arf1 guanine nucleotide exchange factors: evolution, domain structure, and roles in membrane trafficking and human disease

abstract:
  The Sec7 domain ADP-ribosylation factor (Arf) guanine nucleotide exchange factors (GEFs) are found in all eukaryotes, and are involved in membrane remodeling processes throughout the cell. This review is focused on members of the GBF/Gea and BIG/Sec7 subfamilies of Arf GEFs, all of which use the class I Arf proteins (Arf1-3) as substrates, and play a fundamental role in trafficking in the endoplasmic reticulum (ER)—Golgi and endosomal membrane systems. Members of the GBF/Gea and BIG/Sec7 subfamilies are large proteins on the order of 200 kDa, and they possess multiple homology domains. Phylogenetic analyses indicate that both of these subfamilies of Arf GEFs have members in at least five out of the six eukaryotic supergroups, and hence were likely present very early in eukaryotic evolution. The homology domains of the large Arf1 GEFs play important functional roles, and are involved in interactions with numerous protein partners. The large Arf1 GEFs have been implicated in several human diseases. They are crucial host factors for the replication of several viral pathogens, including poliovirus, coxsackievirus, mouse hepatitis coronavirus, and hepatitis C virus. Mutations in the BIG2 Arf1 GEF have been linked to autosomal recessive periventricular heterotopia, a disorder of neuronal migration that leads to severe malformation of the cerebral cortex. Understanding the roles of the Arf1 GEFs in membrane dynamics is crucial to a full understanding of trafficking in the secretory and endosomal pathways, which in turn will provide essential insights into human diseases that arise from misregulation of these pathways.


id: cord-257754-pqxkyg8z
title: Membrane Origin for Autophagy
author: Reggiori, Fulvio
date: 2006-07-21
txt: ./txt/cord-257754-pqxkyg8z.txt
cache: ./cache/cord-257754-pqxkyg8z.txt
extension: .txt
mime: text/plain
url: https://api.elsevier.com/content/article/pii/S0070215306740017
doi: 10.1016/s0070-2153(06)74001-7
summary:
  In addition, a study analyzing conditional knock-out mice defective for autophagy has revealed that the mutant animal accumulates numerous ubiquitinated aggregates in the cytosol, suggesting that this covalent protein modification could serve to specifically target to autophagosomes large structures that have to be eliminated (Komatsu et al., 2005) . In contrast to mammalian cells where several isolation membranes can be simultaneously activated, a single perivacuolar site of organization for double-membrane vesicle formation (named the pre-autophagosomal structure, PAS) is observed in the yeast S. Because the three mammalian Atg8 homologs are diVerently expressed in various tissues (Tanida et al., 2004) , another intriguing option is that these proteins are involved in supplying the autophagosome with membranes derived from diVerent compartments depending on the cell type; for example, GATE-16 from the Golgi complex and GABARAP from the same organelle as well as the synaptic cisternae (Kittler et al., 2001; Kneussel et al., 2000; Sagiv et al., 2000) .

abstract:
  Autophagy is a degradative transport route conserved among all eukaryotic organisms. During starvation, cytoplasmic components are randomly sequestered into large double‐membrane vesicles called autophagosomes and delivered into the lysosome/vacuole where they are destroyed. Cells are able to modulate autophagy in response to their needs, and under certain circumstances, cargoes, such as aberrant protein aggregates, organelles, and bacteria can be selectively and exclusively incorporated into autophagosomes. As a result, this pathway plays an active role in many physiological processes, and it is induced in numerous pathological situations because of its ability to rapidly eliminate unwanted structures. Despite the advances in understanding the functions of autophagy and the identification of several factors, named Atg proteins that mediate it, the mechanism that leads to autophagosome formation is still a mystery. A major challenge in unveiling this process arises from the fact that the origin and the transport mode of the lipids employed to compose these structures is unknown. This compendium will review and analyze the current data about the possible membrane source(s) with a particular emphasis on the yeast Saccharomyces cerevisiae, the leading model organism for the study of autophagosome biogenesis, and on mammalian cells. The information acquired investigating the pathogens that subvert autophagy in order to replicate in the host cells will also be discussed because it could provide important hints for solving this mystery.


id: cord-264468-3oxzzxnd
title: SseG, a virulence protein that targets Salmonella to the Golgi network
author: Salcedo, Suzana P.
date: 2003-10-01
txt: ./txt/cord-264468-3oxzzxnd.txt
cache: ./cache/cord-264468-3oxzzxnd.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/14517239/
doi: 10.1093/emboj/cdg517
summary:
  Similar results were obtained using an antibody against TGN46, a glycoprotein the subcellular localization of GFP-expressing wild-type S.typhimurium (wt-GFP, green) in relation to the cis-Golgi protein giantin (red), and the host cell (DIC in merged image), 8 h after invasion. Since SseG is required for both Golgi localization of bacteria and intracellular replication, we hypothesized that the Golgi network might be exploited by Confocal immuno¯uorescence microscopy of HeLa cells infected for 10 h by GFP-expressing wild-type strain or the sseG mutant as a control. The protein was concentrated in a perinuclear region, where it co-localized extensively with Golgi markers including giantin (data not shown) and Cells expressing a myc-tagged version of SseG (green) were co-labelled with an antibody against TGN46 (red), and examined by confocal microscopy. HeLa cells expressing myc::SseG were incubated with BFA and ®xed for immuno¯uorescence The translocation of the SPI-2 TTSS effector SifA is required for recruitment of lgp-containing vesicles and the formation of Sifs, while SseG localizes SCVs to the Golgi network.

abstract:
  Intracellular replication of the bacterial pathogen Salmonella enterica occurs in membrane-bound compartments called Salmonella-containing vacuoles (SCVs). Maturation of the SCV has been shown to occur by selective interactions with the endocytic pathway. We show here that after invasion of epithelial cells and migration to a perinuclear location, the majority of SCVs become surrounded by membranes of the Golgi network. This process is dependent on the Salmonella pathogenicity island 2 type III secretion system effector SseG. In infected cells, SseG was associated with the SCV and peripheral punctate structures. Only bacterial cells closely associated with the Golgi network were able to multiply; furthermore, mutation of sseG or disruption of the Golgi network inhibited intracellular bacterial growth. When expressed in epithelial cells, SseG co-localized extensively with markers of the trans-Golgi network. We identify a Golgi-targeting domain within SseG, and other regions of the protein that are required for localization of bacteria to the Golgi network. Therefore, replication of Salmonella in epithelial cells is dependent on simultaneous and selective interactions with both endocytic and secretory pathways.


id: cord-264996-og3sg0qw
title: Cell Biology of Membrane Trafficking in Human Disease
author: Howell, Gareth J.
date: 2006-09-17
txt: ./txt/cord-264996-og3sg0qw.txt
cache: ./cache/cord-264996-og3sg0qw.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/16984815/
doi: 10.1016/s0074-7696(06)52005-4
summary:
  Many of these transport intermediates or vesicles, whether derived from the ER, other internal organelles, or the plasma membrane, are ''''coated'''' with unique protein complexes, tethering factors, and regulatory factors that ensure correct targeting to an acceptor compartment. Breast cancer Caveolin-1 Deletion or dominant negative mutation of caveolin-1 promotes tumor progression Breast cancer (Bouras et al., 2004; Williams and Lisanti, 2005) (Hayasaka et al., 1993; Matsuyama et al., 2002) Chediak-Higashi syndrome (CHS) CHS1/Lyst Lyst involved in regulation of protein secretion from lysosomes -enlarged lysosomes Partial albinism, recurrent bacterial infections, impaired chemotaxis and abnormal natural killer cell function (Shiflett et al., 2002; Ward et al., 2003) 214500 Choroideremia (CHM) Rab Escort Protein 1 (REP1) RAB27a remains cytosolic due to defective geranylgeranyl modification in CHM lymphoblasts X-linked form of retinal degeneration 303100 Various mechanisms control the traYcking of proteins from the TGN by the formation and delivery of membrane-derived transport vesicles to the plasma membrane, endosomes, or lysosomal structures (Ponnambalam and Baldwin, 2003) .

abstract:
  Understanding the molecular and cellular mechanisms underlying membrane traffic pathways is crucial to the treatment and cure of human disease. Various human diseases caused by changes in cellular homeostasis arise through a single gene mutation(s) resulting in compromised membrane trafficking. Many pathogenic agents such as viruses, bacteria, or parasites have evolved mechanisms to subvert the host cell response to infection, or have hijacked cellular mechanisms to proliferate and ensure pathogen survival. Understanding the consequence of genetic mutations or pathogenic infection on membrane traffic has also enabled greater understanding of the interactions between organisms and the surrounding environment. This review focuses on human genetic defects and molecular mechanisms that underlie eukaryote exocytosis and endocytosis and current and future prospects for alleviation of a variety of human diseases.


id: cord-265887-g5zhoyo9
author: Mukherjee, Shruti
date: 2020-08-11
txt: ./txt/cord-265887-g5zhoyo9.txt
cache: ./cache/cord-265887-g5zhoyo9.txt
extension: .txt
mime: text/plain
url: https://api.elsevier.com/content/article/pii/S0301462220301605
doi: 10.1016/j.bpc.2020.106452
summary:
  (56) Apart from these highly conserved sequences throughout the genus, there are distinct potent glycosylation sites along the stretch that can serve as chaperone interacting motifs to help in the protein folding and/or aid in J o u r n a l P r e -p r o o f Journal Pre-proof trafficking along with the cellular machinery.(57) Glycosylation of particular asparagine residues (Asn 45, Asn 48, Asn 64, and Asn 68) in the SARS-CoV has been shown to be crucial in maintaining the proteinoligomerization events associated with the host membranes. (41) The formation of a disulfide bond may also play a crucial role in the oligomerization of the E protein, forming stable dimers, trimers, and pentamers depending on its functional requirement.(105) Thus even though the TMD spans the lipid bilayer, the CxxC motif could serve as an essential key to defining the membrane-associated oligomerization events-providing newer targets for preemptive therapeutic intervention.

title:
  Host-membrane interacting interface of the SARS coronavirus envelope protein: Immense functional potential of C-terminal domain

abstract:
  The Envelope (E) protein in SARS Coronavirus (CoV) is a small structural protein, incorporated as part of the envelope. A major fraction of the protein has been known to be associated with the host membranes, particularly organelles related to intracellular trafficking, prompting CoV packaging and propagation. Studies have elucidated the central hydrophobic transmembrane domain of the E protein being responsible for much of the viroporin activity in favor of the virus. However, newer insights into the organizational principles at the membranous compartments within the host cells suggest further complexity of the system. The lesser hydrophobic Carboxylic-terminal of the protein harbors interesting amino acid sequences- suggesting at the prevalence of membrane-directed amyloidogenic properties that remains mostly elusive. These highly conserved segments indicate at several potential membrane-associated functional roles that can redefine our comprehensive understanding of the protein. This should prompt further studies in designing and characterizing of effective targeted therapeutic measures.


id: cord-268527-wbfnhedy
title: Transient hyperglycosylation of rhodopsin with galactose
author: Smith, Sylvia B.
date: 1991-10-31
url: https://www.sciencedirect.com/science/article/pii/001448359190170J
doi: 10.1016/0014-4835(91)90170-j
abstract:
  Abstract Rhodopsin's oligosaccharide chains contain predominantly two types of sugar residues: mannose and N-acetylglucosamine. In the present work, bovine and rat rhodopsin were analysed biochemically for the presence of a third sugar, galactose. Treatment of bovine rod outer segments (ROS) with galactose oxidase followed by reduction with tritium-labeled sodium borohydride revealed the presence of existing molecules of galactose on rhodopsin. Rats injected intravitreally with [3H]galactose and [14C]leucine and maintained in darkness were killed 1 hr, 6 hr, 1, 3, or 5 days following the injection. Retinas were collected for subcellular fractionation and rhodopsin from each of the fractions was purified by ConA sepharose chromatography and SDS-PAGE. During the first 6 hr, galactose selectively labeled rhodopsin in the Golgi-enriched fraction resulting in increased [3H] [14C] ratios in both Golgi and ROS. The data suggested that trimming was occurring at the transition from Golgi to ROS. Furthermore, a decrease in isotope ratio in the ROS between 6 hr and 1 day suggested further trimming of rhodopsin after membrane assembly in the ROS. Additional in vivo experiments demonstrated existing molecules of galactose on rhodopsin's oligosaccharide chain using lectin affinity chromatography. Rats injected intravitreally with [35S]methionine were dark-adapted for 2 hr. Following subcellular fractionation of retinas, ConA purified rhodopsin from ROS was applied to one of two additional lectin columns: Ricinus communis agglutinin (RCA) or Griffonia simplicifolia I (GSA). Eight to nine per cent of the labeled rhodopsin was bound to and eluted from RCA, whereas none bound to GSA, indicating the presence of a β-galactoside. The RCA agarose eluted protein co-electrophoresed with a rhodopsin standard and was light sensitive. Galactose was shown to be the terminal sugar on this subset of rhodopsin and was not capped by neuraminic acid. Binding of rhodopsin's oligosaccharide to RCA was abolished by pre-treatment with β-galactosidase. Decreased binding of rhodopsin to RCA was observed following intravitreal injection of castanospermine but not swainsonine. Of those two inhibitors of glycoprotein trimming, only castanospermine would be expected to prevent the addition of galactose to the oligosaccharide. The association of galactose with rat rhodopsin appeared to be a transient one. At 2 hr, 8–9% of rhodopsin contained galactose, at 6 hr only 2·2% had galactose and by 24 hr less than 1% did. The galactose was trimmed from rhodopsin's oligosaccharide presumably after its role was complete. Separation of rhodopsin of the plasma membranes from rhodopsin of discs indicated that 75% of the galactose-containing rhodopsin was in the plasma membrane and only 25% was in the discs. These findings suggested a possible role for galactose in new disc formation with subsequent removal after the discs are sealed.


id: cord-269011-230p8rsf
title: Molecular Interactions in the Assembly of Coronaviruses
author: de Haan, Cornelis A.M.
date: 2005-08-31
txt: ./txt/cord-269011-230p8rsf.txt
cache: ./cache/cord-269011-230p8rsf.txt
extension: .txt
mime: text/plain
url: https://www.sciencedirect.com/science/article/pii/S0065352705640067
doi: 10.1016/s0065-3527(05)64006-7
summary:
  Biochemical and theoretical studies led to a topological model for the MHV M protein Rottier et al., 1984 Rottier et al., , 1986 , in which the polypeptide spans the lipid bilayer three times, leaving a small amino-terminal domain (15-35 residues) in the lumen of intracellular organelles (or outside the virus), whereas the carboxyterminal half of the protein is located on the cytoplasmic side of the membrane (or inside the virion). Using a mutational approach including deletions, insertions, and substitutions, both the transmembrane domain and the cysteine-rich region immediately downstream thereof, but not the carboxy-terminal part of the cytoplasmic tail, were shown to be important for MHV S protein-induced cell-cell fusion (Bos et al., 1995; Chang and Gombold, 2001; Chang et al., 2000) The cleavage requirements of the S proteins for the biological activities of the coronavirus spike remain enigmatic.

abstract:
  This chapter describes the interactions between the different structural components of the viruses and discusses their relevance for the process of virion formation. Two key factors determine the efficiency of the assembly process: intracellular transport and molecular interactions. Many viruses have evolved elaborate strategies to ensure the swift and accurate delivery of the virion components to the cellular compartment(s) where they must meet and form (sub) structures. Assembly of viruses starts in the nucleus by the encapsidation of viral DNA, using cytoplasmically synthesized capsid proteins; nucleocapsids then migrate to the cytosol, by budding at the inner nuclear membrane followed by deenvelopment, to pick up the tegument proteins.


id: cord-271501-yjobthaj
author: Hirschberg, Carlos B.
date: 1997-02-17
txt: ./txt/cord-271501-yjobthaj.txt
cache: ./cache/cord-271501-yjobthaj.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/9134422/
doi: 10.1093/glycob/7.2.169
abstract: nan
summary:
  UMP is the antiporter for all undine containing nucleotide sugars (Hirschberg and Snider, 1987; Waldman and Rudnick, 1990; Milla et al., 1992) ; thus, one would expect all these uridine nucleotide sugar transporters to have common structural features facing the lumenal and cytosolic side of the membrane. Recent evidence in mammals and yeast suggests that Golgi membrane transporters play a regulatory role in determining which macromolecules undergo specific posttranslational modifications in the lumen of the Golgi apparatus (Abeijon et al., 1993; Toma et al., 1996) . A combination of genetics and overexpression of wild-type and mutant transporter proteins followed by reconstitution into liposomes should allow determination of structural motifs required for membrane insertion, nucleotide recognition, and specific sugar translocation. What structural features determine that these transporters become localized in the Golgi apparatus and/or the endoplasmic reticulum and not another organelle?

title:
  Transporters of nucleotide sugars, nucleotide sulfate and ATP in the Golgi apparatus membrane: Where next?


id: cord-272467-8heg5iql
title: Expression of coronavirus E1 and rotavirus VP10 membrane proteins from synthetic RNA
author: Armstrong, John
date: 2004-02-19
txt: ./txt/cord-272467-8heg5iql.txt
cache: ./cache/cord-272467-8heg5iql.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/2448319/
doi: 10.1002/jcb.240350206
summary:
  We have expressed the cloned cDNA for glycoproteins from two such viruses, the E1 protein of coronavirus, which buds in the Golgi region, and VP10 protein of rotavirus, which assembles in the endoplasmic reticulum. We are investigating two viral model proteins, one for the endoplasmic reticulum and one for the Golgi complex, with a view to determining the features of each molecule responsible for its correct localisation. RNAs prepared by this method for VPlO and E l were translated efficiencly in reticulocyte lysates, Xenopus oocytes, and cultured CVl cells (Figs. However, not all of the viral protein is restricted to the flattened cisternae of the Golgi complex; some at least is found in smooth membranes which are in the same region of the cell but are in fact continuous with the rough endoplasmic reticulum [ 12, 221 .

abstract:
  Some viruses acquire their envelopes by budding through internal membranes of their host cell. We have expressed the cloned cDNA for glycoproteins from two such viruses, the E1 protein of coronavirus, which buds in the Golgi region, and VP10 protein of rotavirus, which assembles in the endoplasmic reticulum. Messenger RNA was prepared from both cDNAs by using SP6 polymerase and either translated in vitro or injected into cultured CV1 cells or Xenopus oocytes. In CV1 cells, the El protein was localised to the Golgi region and VP10 protein to the endoplasmic reticulum. In Xenopus oocytes, the E1 protein acquired post‐translational modifications indistinguishable from the sialylated, O‐linked sugars found on viral protein, while the VP10 protein acquired endoglycosidase‐H‐sensitive N‐linked sugars, consistent with their localisation to the Golgi complex and endoplasmic reticulum, respectively. Thus the two proteins provide models with which to study targeting to each of these intracellular compartments. When the RNAs were expressed in matured, meiotic oocytes, the VP10 protein was modified as before, but the E1 protein was processed to a much lesser extent than in interphase oocytes, consistent with a cessation of vesicular transport during cell division.


id: cord-276358-so390gp4
author: Nieto-Torres, Jose L.
date: 2015-11-30
txt: ./txt/cord-276358-so390gp4.txt
cache: ./cache/cord-276358-so390gp4.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1016/j.virol.2015.08.010
doi: 10.1016/j.virol.2015.08.010
summary:
  title: Severe acute respiratory syndrome coronavirus E protein transports calcium ions and activates the NLRP3 inflammasome In this report, we demonstrate that SARS-CoV E protein forms protein–lipid channels in ERGIC/Golgi membranes that are permeable to calcium ions, a highly relevant feature never reported before. Previously, we reported that SARS-CoV E protein showed mild selectivity for cations (Na þ and K þ ) when reconstituted in ERGIC/ Golgi membranes, mostly conferred by the negative charges of the lipids (Verdia-Baguena et al., 2012 . Synthetic peptides representing the full-length SARS-CoV E protein, or its transmembrane domain (amino acids 7-38) containing point mutations that inhibited ion channel activity (N15A and V25F), were generated by standard phase synthesis and purified by HPLC, as previously described (Verdia-Baguena et al., 2012) . Severe acute respiratory syndrome-associated coronavirus 3a protein forms an ion channel and modulates virus release Severe acute respiratory syndrome coronavirus envelope protein ion channel activity promotes virus fitness and pathogenesis

title:
  Severe acute respiratory syndrome coronavirus E protein transports calcium ions and activates the NLRP3 inflammasome

abstract:
  Abstract Severe acute respiratory syndrome coronavirus (SARS-CoV) envelope (E) protein is a viroporin involved in virulence. E protein ion channel (IC) activity is specifically correlated with enhanced pulmonary damage, edema accumulation and death. IL-1β driven proinflammation is associated with those pathological signatures, however its link to IC activity remains unknown. In this report, we demonstrate that SARS-CoV E protein forms protein–lipid channels in ERGIC/Golgi membranes that are permeable to calcium ions, a highly relevant feature never reported before. Calcium ions together with pH modulated E protein pore charge and selectivity. Interestingly, E protein IC activity boosted the activation of the NLRP3 inflammasome, leading to IL-1β overproduction. Calcium transport through the E protein IC was the main trigger of this process. These findings strikingly link SARS-CoV E protein IC induced ionic disturbances at the cell level to immunopathological consequences and disease worsening in the infected organism.


id: cord-277566-j3ehiwn9
title: Mouse Hepatitis Coronavirus RNA Replication Depends on GBF1-Mediated ARF1 Activation
author: Verheije, Monique H.
date: 2008-06-13
txt: ./txt/cord-277566-j3ehiwn9.txt
cache: ./cache/cord-277566-j3ehiwn9.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1371/journal.ppat.1000088
doi: 10.1371/journal.ppat.1000088
summary:
  Here, we study the involvement of the secretory pathway in mouse hepatitis coronavirus (MHV) replication by using the drug brefeldin A (BFA), which is known to interfere with ER-Golgi membrane traffic by inhibiting the activation of ADP-ribosylation factor (ARF) small GTPases. Therefore, LR7 cells infected with MHV-A59 were treated with BFA for 30 minutes starting 5.5 h p.i. They were subsequently fixed and processed for immunofluorescence using antibodies both against nsp8, which served as a protein marker for the MHV replication sites [50, 51] , and against the viral structural protein M, known to reside in the Golgi [52] . In complete agreement with the luciferase expression data shown above, this result demonstrates that BFA inhibits, but does not completely block, the formation of RCs. To study the effects of BFA on the DMVs at an ultrastructural level, MHV-infected LR7 cells were fixed at 6 h p.i. and embedded in Epon resin in order to be analyzed by electron microscopy.

abstract:
  Coronaviruses induce in infected cells the formation of double membrane vesicles, which are the sites of RNA replication. Not much is known about the formation of these vesicles, although recent observations indicate an important role for the endoplasmic reticulum in the formation of the mouse hepatitis coronavirus (MHV) replication complexes (RCs). We now show that MHV replication is sensitive to brefeldin A (BFA). Consistently, expression of a dominant-negative mutant of ARF1, known to mimic the action of the drug, inhibited MHV infection profoundly. Immunofluorescence analysis and quantitative electron microscopy demonstrated that BFA did not block the formation of RCs per se, but rather reduced their number. MHV RNA replication was not sensitive to BFA in MDCK cells, which are known to express the BFA-resistant guanine nucleotide exchange factor GBF1. Accordingly, individual knockdown of the Golgi-resident targets of BFA by transfection of small interfering RNAs (siRNAs) showed that GBF1, but not BIG1 or BIG2, was critically involved in MHV RNA replication. ARF1, the cellular effector of GBF1, also appeared to be involved in MHV replication, as siRNAs targeting this small GTPase inhibited MHV infection significantly. Collectively, our results demonstrate that GBF1-mediated ARF1 activation is required for efficient MHV RNA replication and reveal that the early secretory pathway and MHV replication complex formation are closely connected.


id: cord-287477-aios0h8s
title: Role of the early secretory pathway in SARS-CoV-2 infection
author: Sicari, Daria
date: 2020-07-28
txt: ./txt/cord-287477-aios0h8s.txt
cache: ./cache/cord-287477-aios0h8s.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1083/jcb.202006005
doi: 10.1083/jcb.202006005
summary:
  CoV-2 infection starts when its spike (S) protein binds to angiotensin I-converting enzyme 2 (ACE2) receptors on the host cell membrane (Lake, 2020; Letko et al., 2020) . Thus, virion spread critically depends on recruiting the most efficient secretory machineries of host cells (Su et al., 2016; Proteins of the early secretory pathway bound by SARS-CoV-2 As the entire world asks for ways to stop CoV-2, many laboratories are investigating the virus''s Achilles heel(s). The role of glycosylation and protein quality control in SARS-CoV-2 infections Most CoVs bud at the ERGIC level ( Fig. 1) and are then transported along the exocytic pathway (Klumperman et al., 1994; Stertz et al., 2007) . We observed enrichment for five host-derived virus-interacting proteins (GOLGB1, PDE4DIP, TOR1A, HMOX1, and HYOU1) involved in different processes and related to quality control and ER-Golgi homeostasis maintenance.

abstract:
  Similar to other RNA viruses, SARS-CoV-2 must (1) enter a target/host cell, (2) reprogram it to ensure its replication, (3) exit the host cell, and (4) repeat this cycle for exponential growth. During the exit step, the virus hijacks the sophisticated machineries that host cells employ to correctly fold, assemble, and transport proteins along the exocytic pathway. Therefore, secretory pathway–mediated assemblage and excretion of infective particles represent appealing targets to reduce the efficacy of virus biogenesis, if not to block it completely. Here, we analyze and discuss the contribution of the molecular machines operating in the early secretory pathway in the biogenesis of SARS-CoV-2 and their relevance for potential antiviral targeting. The fact that these molecular machines are conserved throughout evolution, together with the redundancy and tissue specificity of their components, provides opportunities in the search for unique proteins essential for SARS-CoV-2 biology that could also be targeted with therapeutic objectives. Finally, we provide an overview of recent evidence implicating proteins of the early secretory pathway as potential antiviral targets with effective therapeutic applications.


id: cord-287815-alv30uk5
title: The Golgi complex: In vitro veritas?
author: Mellman, Ira
date: 1992-03-06
txt: ./txt/cord-287815-alv30uk5.txt
cache: ./cache/cord-287815-alv30uk5.txt
extension: .txt
mime: text/plain
url: https://api.elsevier.com/content/article/pii/009286749290027A
doi: 10.1016/0092-8674(92)90027-a
abstract: nan
summary:
  As we have seen, there are three key elements underlying our general view of the Golgi: that the Golgi consists of several discrete compartments (cis, medial, trans, and TGN) corresponding to individual or groups of cisternae; that transit between these compartments occurs viavesicular carriers; and that the transport process is inherently nonselective with respect to the passenger proteins. While distinct from the CGN or TGN, we assume that the medial cisternae represent a single functionally continuous compartment, irrespective of the actual number of physically separate cisternal elements in any one Golgi complex. Given that VSV G protein in early Golgi compartments was transported with the highest efficiency (Fries and Rothman, 1981) the transport event assayed was postulated to reflect the formation of vesicles from cis (early) cisternae and the fusion of these vesicles with medial cisternae (which contain the GlcNAc transferase) (Rothman and Orci, 1990) (Figure 4) .


id: cord-289710-ucguzgdm
author: nan
date: 1992-12-02
txt: ./txt/cord-289710-ucguzgdm.txt
cache: ./cache/cord-289710-ucguzgdm.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/1469044/
doi: nan
summary:
  In addition to soluble proteins, the cell surface appears to be the default destination for mammalian ER, Golgi, and lysosomal membrane proteins as removal of their respective retention/targeting signals results in their delivery to the plasma membrane (Machamer and Rose, 1987; Jackson et al., 1990; Williams and Fukuda, 1990) . Kexlp is predicted to be a type I transmembrane protein with a large amino-terminal protease domain in the lumen of the secretory pathway, a single membrane-spanning domain, and a smaller carboxy-terminai domain positioned cytoplasmicaUy. The observation that KEX/cells intracellularly retain Kexlp activity prompted an analysis to determine in which secretory compartment Kexlp resided, and how it achieved such retention. The above results indicated that Kexlp-Hpa was membrane associated, had received glycosyl modifications in the Golgi apparatus, gave wild-type levels of total activity, and was retained intracellularly; yet processed the K1 killer toxin precursor to a lesser extent than Kexlp.

title:
  Yeast Kex1p is a Golgi-associated membrane protein: deletions in a cytoplasmic targeting domain result in mislocalization to the vacuolar membrane

abstract:
  We have investigated the localization of Kex1p, a type I transmembrane carboxypeptidase involved in precursor processing within the yeast secretory pathway. Indirect immunofluorescence demonstrated the presence of Kex1p in a punctate organelle resembling the yeast Golgi apparatus as identified by Kex2p and Sec7p (Franzusoff, A., K. Redding, J. Crosby, R. S. Fuller, and R. Schekman. 1991. J. Cell Biol. 112:27- 37). Glycosylation studies of Kex1p were consistent with a Golgi location, as Kex1p was progressively N-glycosylated in an MNN1- dependent manner. To address the basis of Kex1p targeting to the Golgi apparatus, we examined the cellular location of a series of carboxy- terminal truncations of the protein. The results indicate that a cytoplasmically exposed carboxy-terminal domain is required for retention of this membrane protein within the Golgi apparatus. Deletions of the retention region or overproduction of wild-type Kex1p led to mislocalization of Kex1p to the vacuolar membrane. This unexpected finding is discussed in terms of models involving either the vacuole as a default destination for membrane proteins, or by endocytosis to the vacuole following their default localization to the plasma membrane.


id: cord-292688-w4zvfkyl
title: Biogenesis of secretory granules in the trans-Golgi network of neuroendocrine and endocrine cells
author: Tooze, Sharon A
date: 1998-08-14
txt: ./txt/cord-292688-w4zvfkyl.txt
cache: ./cache/cord-292688-w4zvfkyl.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/9714820/
doi: 10.1016/s0167-4889(98)00059-7
summary:
  An alternative hypothesis is that there is very little constitutive secretion originating from the TGN of regulated cells, and that most molecules in the biosynthetic pathway exit into ISGs. In the ISG, the non-secretory granule proteins would presumably be sorted from the regulated secretory proteins via interaction with a receptor and removed from the ISG in constitutive-like vesicles. Depending on the cargo, distinct mechanisms could be used for selection to increase the e¤ciency of removal of nonsecretory granule proteins from the maturing ISGs. While the mechanisms involved in the formation of both constitutive and regulated secretory vesicles from the TGN is largely unknown there have been recent reports which suggest that both these budding reactions maybe unique in that they function independently of known coat proteins. In the PC12 cell assay, the same e¡ect was observed with [AlF 4 ] À and several other lines of evidence demonstrated that heterotrimeric GTP-binding proteins are involved in the regulation of post-Golgi vesicle formation (see [71] for review).

abstract:
  Secretory granule formation requires selection of soluble and membrane proteins into nascent secretory granules, and exclusion of proteins not required for the function of secretory granules. Both selection and exclusion presumably can occur in the compartment where assembly of the secretory granule begins, the trans most cisternae of the Golgi complex. Current research focused on the initial stages of secretory granule formation includes a search for the ‘signals’ which may mediate active sorting of components into secretory granules, and the role of aggregation of regulated secretory proteins in sorting. In addition, the temporal sequence of the sorting events in the Golgi, and post-Golgi compartments has gained much attention, as summarized by the alternative but not mutually exclusive ‘sorting for entry’ vs. ‘sorting by retention’ models. ‘Sorting for entry’ which encompasses the most popular models requires selection of cargo and membrane and exclusion of non-secretory granule proteins in the TGN prior to secretory granule formation. ‘Sorting by retention’ stipulates that protein selection or exclusion may occur after secretory granule formation: secretory granule specific components are retained during maturation of the granule while non-secretory granule molecules are removed in vesicles which bud from maturing secretory granules. Finally, some progress has been made in the identification of cytosolic components involved in the budding of nascent secretory granules from the TGN. This review will focus on the recent data concerning the events in secretory granule formation which occur, in the trans-Golgi network.


id: cord-293038-pjjvfdnq
title: The unique architecture of Bunyamwera virus factories around the Golgi complex
author: Fontana, Juan
date: 2008-06-10
txt: ./txt/cord-293038-pjjvfdnq.txt
cache: ./cache/cord-293038-pjjvfdnq.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/18547336/
doi: 10.1111/j.1462-5822.2008.01184.x
summary:
  We propose that this new structure, unique among enveloped viruses, assembles in association with the most stable component of Golgi stacks, the actin‐containing matrix scaffold, connecting viral replication and morphogenesis inside viral factories. Modified membranes harbouring viral replication complexes (RCs) frequently integrate into a complex structure known as the ''viral factory'' where the cytoskeleton participates, cell organelles are recruited and the different steps of the virus life cycle are sequentially connected. We propose that this new multifunctional structure associates with the actin-containing matrix of the Golgi stacks providing a stable scaffold for viral replication and early morphogenesis. LtA and CyD had very little or no effect, respectively, on viral replication and assembly as determined by measurement of infectious viral particles released to the culture supernatants at 6 and 10 h p.i. Complete tubes, virus budding profiles and viral particles assembled in Golgi stacks of cells treated with LtA, as observed in thin sections of treated cells studied by EM (not shown).

abstract:
  Viral factories are novel structures built by viruses in infected cells. During their construction organelles are recruited and build a large scaffold for viral replication and morphogenesis. We have studied how a bunyavirus uses the Golgi to build the factory. With the help of confocal and 3D ultrastructural imaging together with molecular mapping in situ and in vitro we have characterized a tubular structure that harbours the viral replication complexes in a globular domain. Numerous ribonucleoproteins were released from purified tubes disrupted in vitro. Actin and myosin I were identified by peptide mass fingerprinting in isolated tubes while actin and the viral NSm non‐structural protein were detected in the tubes' internal proteinaceous scaffold by immunogold labelling. Studies with NSm deletion mutants and drugs affecting actin showed that both NSm and actin are key factors for tube and virus assembly in Golgi. Three‐dimensional reconstructions based on oriented serial sections of infected cells showed that tubes anchor cell organelles to Golgi stacks and make contacts with intracellular viruses. We propose that this new structure, unique among enveloped viruses, assembles in association with the most stable component of Golgi stacks, the actin‐containing matrix scaffold, connecting viral replication and morphogenesis inside viral factories.


id: cord-296416-q0rsfzgw
author: LAVI, EHUD
date: 1996-07-15
txt: ./txt/cord-296416-q0rsfzgw.txt
cache: ./cache/cord-296416-q0rsfzgw.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/8661443/
doi: 10.1006/viro.1996.0382
summary:
  In many 3-5 hr after infection, individual elements of the GA, cells the secretion blocker Brefeldin A (BFA) reversibly which are associated initially with separate microtubuleredistributes membranes and enzymes of the GA back organizing centers in perinuclear areas of fused cells, into the RER, but does not inhibit endocytosis (Doms et congregate in the center of syncytia and form an exal., 1989; Lippincott-Schwartz et al., 1989; Johnston et al., tended network of nondisrupted intact Golgi complexes 1994). In this study, we used organ-Immunohistochemistry elle-specific antibodies, immunohistochemistry, and transmission electron microscopy to examine the fate of Cells, grown on poly-D-lysine-treated coverslips, were the GA during cell fusion and syncytia formation in mouse fixed with 2% paraformaldehyde for 20 min at room tem-L-2 cells infected with MHV-A59 and fusion defective perature, washed three times in PBS, then incubated for mutants.

title:
  Syncytia Formation Induced by Coronavirus Infection Is Associated with Fragmentation and Rearrangement of the Golgi Apparatus

abstract:
  Abstract Coronavirus mouse hepatitis virus (MHV) possesses a membrane glycoprotein (M) which is targeted to the Golgi apparatus (GA). We used immunocytochemistry with an organelle-specific antiserum to investigate the morphologic changes of the GA during infection of L2 murine fibroblasts with MHV-A59. Twenty-four hours after infection the GA was fragmented and translocated in the center of syncytia, while the microtubular network was also rearranged displaying radiating elements toward the center of syncytia. Two fusion-defective mutants, which contain an identical amino acid substitution in the cleavage signal sequence of the spike glycoprotein (S), induced fragmentation of the GA. However, the GA migrated only partially to the centers of syncytia during infection with these mutants. Revertant viruses, in which the above mutation was corrected, had fusion properties and GA staining similar to wtMHV-A59. Experiments with brefeldin A (BFA), which induces redistribution of the GA into the rough endoplasmic reticulum (RER), revealed that an intact GA for a period of 4–16 hr postinfection, is required for coronavirus replication and syncytia formation. Thus, during MHV infection, syncytia formation is associated with fragmentation of the GA, followed by a previously undescribed phenomenon of migration of the organelle into the centers of syncytia. The fragmentation of the GA, however, may occur without the formation of syncytia. Therefore, two distinct mechanisms may be responsible for the fragmentation of the GA and its subsequent migration to the center of syncytia.


id: cord-298251-u36lb44w
title: Arf Family G Proteins and their regulators: roles in membrane transport, development and disease
author: Donaldson, Julie G.
date: 2011-05-18
url: https://www.ncbi.nlm.nih.gov/pubmed/21587297/
doi: 10.1038/nrm3117
abstract:
  Members of the ADP-ribosylation factor (ARF) family of guanine-nucleotide-binding (G) proteins, including the ARF-like (ARL) proteins and SAR1, regulate membrane traffic and organelle structure by recruiting cargo-sorting coat proteins, modulating membrane lipid composition, and interacting with regulators of other G proteins. New roles of ARF and ARL proteins are emerging, including novel functions at the Golgi complex and in cilia formation. Their function is under tight spatial control, which is mediated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) that catalyse GTP exchange and hydrolysis, respectively. Important advances are being gained in our understanding of the functional networks that are formed not only by the GEFs and GAPs themselves but also by the inactive forms of the ARF proteins.


id: cord-298503-l60cdllh
author: Saraste, J.
date: 2015-08-20
url: https://www.sciencedirect.com/science/article/pii/B9780123944474200138
doi: 10.1016/b978-0-12-394447-4.20013-8
title:
  Intermediate Compartment: A Sorting Station between the Endoplasmic Reticulum and the Golgi Apparatus

abstract:
  The intermediate compartment (IC) is a pleiomorphic membrane system that mediates two-way trafficing in the early biosynthetic-secretory pathway of mammalian cells. The IC associates with the cytoskeleton, binds COPI (coat protein I) coats and generates vesicular, tubular and saccular transport carriers. It recieves newly made proteins and lipids from the endoplasmic reticulum (ER) and sorts them for transport to the Golgi apparatus or recycling back to the ER. Although the IC appears to be functionally complex and resides at the crossroads of multiple transport routes, it is still disputed whether it represents a transient or stable structure.


id: cord-299281-5z1xminb
title: Oligomerization of a membrane protein correlates with its retention in the Golgi complex
author: nan
date: 1993-09-02
txt: ./txt/cord-299281-5z1xminb.txt
cache: ./cache/cord-299281-5z1xminb.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/8397214/
doi: nan
summary:
  Our data suggest that SDS-resistant oligomers form as newly synthesized molecules of Gml arrive at the Golgi complex and may interact (directly or indirectly) with an actinbased cytoskeletal matrix. Together, these observations suggest that SDS-resistant oligomer formation is an intrinsic property of Gml and mutant Gml proteins that are retained in the Golgi complex, but not of mutants that efficiently reach the plasma membrane. HeLa cells expressing Gml were metabolically labeled for 5 min, chased for the indicated times, solubilized, and immunoprecipitated with anti-VSV G antibody (Fig. 3) . HeLa cells expressing Gml or VSV G were metabolically radiolabeled for 5 min, and then chased for 0 or 60 rain, and microsomes prepared as described in Materials and Methods. On sucrose gradients, Gml solubilized from cytochalasin D-treated cells migrated as an SDS-sensitive oligomer (in the pellet), and VSV G trimerization was unaffected (data not shown).

abstract:
  The first membrane-spanning domain (m1) of the M glycoprotein of avian coronavirus (formerly called E1) is sufficient to retain this protein in the cis-Golgi. When the membrane-spanning domain of a protein which is efficiently delivered to the plasma membrane (VSV G protein) is replaced with m1, the resulting chimera (Gm1) is retained in the Golgi (Swift, A. M., and C. E. Machamer. 1991. J. Cell Biol. 115:19-30). When assayed in sucrose gradients, we observed that Gm1 formed a large oligomer, and that much of this oligomer was SDS resistant and stayed near the top of the stacking gel of an SDS-polyacrylamide gel. The unusual stability of the oligomer allowed it to be detected easily. Gm1 mutants with single amino acid substitutions in the m1 domain that were retained in the Golgi complex formed SDS-resistant oligomers, whereas mutants that were rapidly released to the plasma membrane did not. Oligomerization was not detected immediately after synthesis of Gm1, but occurred gradually with a lag of approximately 10 min, suggesting that it is not merely aggregation of misfolded proteins. Furthermore, oligomerization did not occur under several conditions that block ER to Golgi transport. The lumenal domain was not required for oligomerization since another chimera (alpha m1G), where the lumenal domain of Gm1 was replaced by the alpha subunit of human chorionic gonadotropin, also formed an SDS-resistant oligomer, and was able to form hetero-oligomers with Gm1 as revealed by coprecipitation experiments. SDS resistance was conferred by the cytoplasmic tail of VSV G, because proteolytic digestion of the tail in microsomes containing Gm1 oligomers resulted in loss of SDS resistance, although the protease-treated material continued to migrate as a large oligomer on sucrose gradients. Interestingly, treatment of cells with cytochalasin D blocked formation of SDS-resistant (but not SDS- sensitive) oligomers. Our data suggest that SDS-resistant oligomers form as newly synthesized molecules of Gm1 arrive at the Golgi complex and may interact (directly or indirectly) with an actin-based cytoskeletal matrix. The oligomerization of Gm1 and other resident proteins could serve as a mechanism for their retention in the Golgi complex.


id: cord-303153-z7bdiuvx
author: Ulasli, Mustafa
date: 2010-01-20
url: https://doi.org/10.1111/j.1462-5822.2010.01437.x
doi: 10.1111/j.1462-5822.2010.01437.x
title:
  Qualitative and quantitative ultrastructural analysis of the membrane rearrangements induced by coronavirus

abstract:
  Coronaviruses (CoV) are enveloped positive‐strand RNA viruses that induce different membrane rearrangements in infected cells in order to efficiently replicate and assemble. The origin, the protein composition and the function of these structures are not well established. To shed further light on these structures, we have performed a time‐course experiment in which the mouse hepatitis virus (MHV)‐induced membrane rearrangements were examined qualitatively and quantitatively by (immuno)‐electron microscopy. With our approach we were able to confirm the appearance of 6, previously reported, membranous structures during the course of a complete infection cycle. These structures include the well‐characterized double‐membrane vesicles (DMVs), convoluted membranes (CMs) and virions but also the more enigmatic large virion‐containing vacuoles (LVCVs), tubular bodies (TBs) and cubic membrane structures (CMSs). We have characterized the LVCVs, TBs and CMSs, and found that the CoV‐induced structures appear in a strict order. By combining these data with quantitative analyses on viral RNA, protein synthesis and virion release, this study generates an integrated molecular and ultrastructural overview of CoV infection. In particular, it provides insights in the role of each CoV‐induced structure and reveals that LVCVs are ERGIC/Golgi compartments that expand to accommodate an increasing production of viral particles.


id: cord-306067-ldn17pj8
author: Inoue, Satoshi
date: 2003-12-19
txt: ./txt/cord-306067-ldn17pj8.txt
cache: ./cache/cord-306067-ldn17pj8.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/14717703/
doi: 10.1046/j.1432-1033.2003.03934.x
summary:
  These results suggest that the 30-kDa component is the ER form of fhx/P25 and the 27-kDa component represents fhx/P25 whose N-linked oligosaccharide chains lost their terminal a1,2-mannose residues by digestion with a1,2-manosidases in Golgi complex, and further imply that fhx/P25 in the elementary unit of the normal-level fibroin-producing breeds is largely resistant to the action of a1,2-mannosidases in Golgi complex and secreted as the ER-type 30-kDa form. It is thus conceivable that in the Nd-s D mutant silkworm, fhx/P25 in the L-chain-free H 6 fhx 1 -type elementary unit (Table 2) is processed efficiently by the action of Golgi a1,2-mannosidases to yield only the 27-kDa molecule in the secreted fibroin. In order to examine a role of L-chain in the protection of a1,2-mannose residues of fhx/P25 in the elementary unit, the Nd-s D mutant silkworm was subjected to transgenesis with the normal L-chain promoter/cDNA sequence together with a marker gene of DsRed2 (Fig. 4A) , and two transgenic lines L6 · 7 and L7-4 were selected.

title:
  Assembly of the silk fibroin elementary unit in endoplasmic reticulum and a role of L‐chain for protection of α1,2‐mannose residues in N‐linked oligosaccharide chains of fibrohexamerin/P25

abstract:
  Silk fibroin of Bombyx mori is secreted from the posterior silk gland (PSG) as a 2.3‐MDa elementary unit, consisting of six sets of a disulfide‐linked heavy chain (H‐chain)–light chain (L‐chain) heterodimer and one molecule of fibrohexamerin (fhx)/P25. Fhx/P25, a glycoprotein, associates noncovalently with the H–L heterodimers. The elementary unit was found and purified from the endoplasmic reticulum (ER) extract of PSG cells. A substantial amount of fhx/P25 unassembled into the elementary unit was also present in ER. In normal‐level fibroin‐producing breeds (J‐139 and C108), the elementary unit contained fhx/P25 of either 30 kDa (major) or 27 kDa (minor). The 27‐kDa fhx/P25 was produced from the 30‐kDa form by digestion with the bacterial α1,2‐mannosidase in vitro. The elementary unit in the ER extract contained only the 30‐kDa fhx/P25, whereas both 30‐ and 27‐kDa forms of fhx/P25 were present in the ER plus Golgi mixed extracts. In naked‐pupa mutants [Nd(2), Nd‐s and Nd‐s (D)], extremely small amounts of fibroin were produced and they consisted of one molecule of 27‐kDa fhx/P25 and six molecules of H‐chain but no L‐chain. When the Nd‐s (D) mutant was subjected to transgenesis with the normal L‐chain gene, the (H‐L)(6)fhx(1)‐type elementary unit containing the 30‐kDa fhx/P25, was produced. These results suggest that fhx/P25 in the elementary unit is largely protected from digestion with Golgi α1,2‐mannosidases when L‐chains are present in the unit. Models suggesting a role of L‐chain for the protection of α1,2‐mannose residues of fhx/P25 are presented.


id: cord-309384-vlk8cebh
title: Ganglioside Biochemistry
author: Kolter, Thomas
date: 2012-12-19
txt: ./txt/cord-309384-vlk8cebh.txt
cache: ./cache/cord-309384-vlk8cebh.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/25969757/
doi: 10.5402/2012/506160
summary:
  A principal difference between ganglioside biosynthesis in the Golgi apparatus and degradation in the endolysosomal compartment is that during GSL formation, membranebound glycosyltransferases interact with their membranebound glycolipid substrates by diffusion within the twodimensional plane of the lipid bilayer. As glycosidase substrates, GSLs with four carbohydrate residues or less require the additional presence of small lipid binding glycoproteins, either the GM2 activator protein or one of the four saposins A-D. In vitro, in addition to enzymes and activator proteins, also an appropriate membrane-lipid composition of the ganglioside-containing membrane is required for degradation [222] . Due to the deficiency of two enzyme activities, β-hexosaminidases A and B, storage of negatively charged glycolipids characteristic for Tay-Sachs disease and, in addition, of uncharged substrates such as GA2 in the brain and globoside in visceral organs (Figure 16 ) is observed.

abstract:
  Gangliosides are sialic acid-containing glycosphingolipids. They occur especially on the cellular surfaces of neuronal cells, where they form a complex pattern, but are also found in many other cell types. The paper provides a general overview on their structures, occurrence, and metabolism. Key functional, biochemical, and pathobiochemical aspects are summarized.


id: cord-313694-p2sgaypq
title: Current ideas on the significance of protein glycosylation
author: West, Christopher M.
date: 1986
txt: ./txt/cord-313694-p2sgaypq.txt
cache: ./cache/cord-313694-p2sgaypq.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/3029560/
doi: 10.1007/bf00230632
summary:
  The alternate view is that carbohydrate structures participate in numerous specific interactions with discrete protein receptors, and that these interactions lead to predictable modifications in the localization or activity of the glycoprotein. The notion of a ''non-specific'' role for carbohydrate has received perhaps its strongest support from studies on cells whose glycosylation processes have been globally altered by mutation or drugs. Consideration of the possible role of carbohydrate in other molecular associations with the plasma membrane will be considered below in sections on hormone-receptor interactions and cellsubstratum (e.g., extracellular matrix) and cell-cell adhesion. Considerable evidence has been adduced that various parasites such as viruses, bacteria, protozoa, etc., possess carbohydrate binding proteins which can interact with sugar structures on the surfaces of cells with which the parasites associate (167, 168, (116) (117) (118) (119) . In any case, antibodies and lectins may model potential receptors in cells which might specifically recognize carbohydrate-associated structures.

abstract:
  Carbohydrate has been removed from a number of glycoproteins without major effect on the structure or enzyme activity of the protein. Thus carbohydrate has been suggested to underly a non-primary function for proteins, such as in relatively non-specific interactions with other carbohydrates or macromolecules, stabilization of protein conformation, or protection from proteolysis. This non-specific concept is consistent with both the general similarity in carbohydrate structure on very diverse glycoproteins and the frequent structural microheterogeneity of carbohydrate chains at given sites. The concept is supported in a general sense by the viability of cells whose glycosylation processes have been globally disrupted by mutation or pharmacological inhibitors. In contrast to the above observations, other studies have revealed the existence of specific, selective receptors for discrete oligosaccharide structures on glycoproteins which seem to be important for compartmentalization of the glycoprotein, or the positioning of cells on which the glycoprotein is concentrated. Sometimes multivalency in the carbohydrate-receptor interaction is crucial. There are additional possible roles for carbohydrate in the transduction of information upon binding to a receptor. The possibility of specific roles for carbohydrate is supported by the existence of numerous unique carbohydrate structures, many of which have been detected as glycoantigens by monoclonal antibodies, with unique distributions in developing and differentiated cells. This article attempts to summarize and rationalize the contradictory results. It appears that in general carbohydrate does in fact underlie only roles secondary to a protein's primary function. These secondary roles are simple non-specific ones of protection and stabilization, but often also satisfy the more sophisticated needs of spatial position control and compartmentalization in multicellular eukaryotic organisms. It is suggested that there are advantages, evolutionarily speaking, for the shared use of carbohydrate for non-specific roles and for specific roles primarily as luxury functions to be executed during the processes of cell differentiation and morphogenesis.


id: cord-317070-awip52k7
author: nan
date: 1993-07-01
txt: ./txt/cord-317070-awip52k7.txt
cache: ./cache/cord-317070-awip52k7.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/8315394/
doi: nan
summary:
  Changes to the structure and distribution of the Golgi complex antigens were followed by indirect immunoperoxidase staining (47) using the prototype serum SY, rabbit antibodies to the recombinant SY2, SY10, and SYll proteins, and affnity-pufifed antibodies as described above. When antibodies from the prototype serum were affinity purified on nitrocellulose filters containing 5 x 104 phage-expressing SY2 and SYll recombinant proteins, all reproduced the Golgi pattern of immunofluorescence on HEp-2 cells (Fig. 1 b) . The 35S-labeled in vitro translation product of SYll cDNA migrated in SDS-PAGE at 95 kD ( Fig. 8 b, lane I) and was immunoprecipitated by the original human anti-Golgi serum (Fig. 8 b, lane 3) . Evidence that the rabbit antiserum raised by immunization with recombinant SY11 recognized the same protein as the prototype human serum was shown when the rabbit antiserum immunoprecipitated the in vitro translation product in an identical manner to human Golgi sera (Fig. 8 b, compare lanes 3 and 5 with lane 4).

title:
  Molecular characterization of two human autoantigens: unique cDNAs encoding 95- and 160-kD proteins of a putative family in the Golgi complex

abstract:
  Serum autoantibodies from a patient with autoantibodies directed against the Golgi complex were used to screen clones from a HepG2 lambda Zap cDNA library. Three related clones, designated SY2, SY10, and SY11, encoding two distinct polypeptides were purified for further analysis. Antibodies affinity purified by adsorption to the lambda Zap- cloned recombinant proteins and antibodies from NZW rabbits immunized with purified recombinant proteins reproduced Golgi staining and bound two different proteins, 95 and 160 kD, from whole cell extracts. The SY11 protein was provisionally named golgin-95 and the SY2/SY10 protein was named golgin-160. The deduced amino acid sequence of the cDNA clone of SY2 and SY11 represented 58.7- and 70-kD proteins of 568 and 620 amino acids. The in vitro translation products of SY2 and SY11 cDNAs migrated in SDS-PAGE at 65 and 95 kD, respectively. The in vitro translated proteins were immunoprecipitated by human anti-Golgi serum or immune rabbit serum, but not by normal human serum or preimmune rabbit serum. Features of the cDNA suggested that SY11 was a full- length clone encoding golgin-95 but SY2 and SY10 together encoded a partial sequence of golgin-160. Analysis of the SY11 recombinant protein identified a leucine zipper spanning positions 419-455, a glutamic acid-rich tract spanning positions 322-333, and a proline-rich tract spanning positions 67-73. A search of the SwissProt data bank indicated sequence similarity of SY11 to human restin, the heavy chain of kinesin, and the heavy chain of myosin. SY2 shared sequence similarity with the heavy chain of myosin, the USO1 transport protein from yeast, and the 150-kD cytoplasmic dynein-associated polypeptide. Sequence analysis demonstrated that golgin-95 and golgin-160 share 43% sequence similarity and, therefore, may be functionally related proteins.


id: cord-319626-f1b3ygg0
title: Site of addition of N-acetyl-galactosamine to the E1 glycoprotein of mouse hepatitis virus-A59
author: nan
date: 1988-05-01
txt: ./txt/cord-319626-f1b3ygg0.txt
cache: ./cache/cord-319626-f1b3ygg0.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/2836431/
doi: nan
summary:
  After synthesis in the rough ER this protein is transported to a smooth membrane compartment between the rough ER and Golgi stack where it accumulates allowing nucleocapsids in the cytoplasm to bind which results in the formation of a virion (Holmes et al., 1981a; Tooze et al., 1984) . The observed increases in molecular mass must be due to the addition of O-linked oligosaccharides (Holmes et al., 1981a; Niemann and Klenk, 1981; Rottier et al., 1981) , which is the only known posttranslational modification of El. The intermediate form EI~ has not, however, been previously detected and the heterogeneity of mature forms resolved in Fig. 1 was not seen in previous work with the same virus propagated in a different cell line (e.g., Niemann et al., 1982) .

abstract:
  By pulse-chase labeling with [35S]methionine and long-term labeling with 3H-sugars, the E1 glycoprotein of coronavirus MHV-A59 has been shown to acquire O-linked oligosaccharides in a two-step process. About 10 min after synthesis of the E1 protein, N-acetyl-galactosamine was added. This was followed approximately 10 min later by the addition of both galactose and sialic acid to give the mature oligosaccharides. This sequence of additions was confirmed by analyzing the 3H-labeled oligosaccharides bound to each of the E1 forms using gel filtration on P4 columns. The intracellular location of the first step was determined by exploiting the temperature sensitivity of virus release. The virus normally buds first into a smooth membrane compartment lying between the rough endoplasmic reticulum and the cis side of the Golgi stack (Tooze et al., 1984). At 31 degrees C the virus is assembled but does not appear to enter the Golgi stacks. The addition of N-acetyl- galactosamine is unaffected although the addition of galactose and sialic acid is inhibited. These results strongly suggest that addition of N-acetyl-galactosamine occurs in this budding compartment, the morphology of which is similar to that of transitional elements and vesicles.


id: cord-322516-wekvet6f
author: Maceyka, Michael
date: 1997-12-15
txt: ./txt/cord-322516-wekvet6f.txt
cache: ./cache/cord-322516-wekvet6f.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/9396747/
doi: nan
summary:
  Short-term treatment with two inhibitors of sphingolipid synthesis had no effect on localization of IBV M or other Golgi markers. Treatment of cells with 100 M PDMP for 1 h had no effect on the localization of either protein (Fig. 4) , suggesting that the morphology of the Golgi was not greatly altered. Pretreatment with the earlier inhibitors reduced the PDMP-induced slowing of anterograde traffic by about half, suggesting that accumulation of newly synthesized ceramide at least partially mediates this effect. The pretreatment experiments suggested that increased levels of ceramide mediate the PDMP-induced effects on IBV M localization. However, neither ␤CA nor FB1 had an effect on the rate of anterograde traffic of VSV G or the localization of IC, CGN, or Golgi stack proteins. However, the glucosylceramide analogue PDMP, at a concentration that inhibits both GlcCer and SM synthases, causes a redistribution of IBV M to the ER and a slowing of anterograde traffic in BHK-21 cells.

title:
  Ceramide Accumulation Uncovers a Cycling Pathway for the cis-Golgi Network Marker, Infectious Bronchitis Virus M Protein

abstract:
  The M glycoprotein from the avian coronavirus, infectious bronchitis virus (IBV), contains information for localization to the cis-Golgi network in its first transmembrane domain. We hypothesize that localization to the Golgi complex may depend in part on specific interactions between protein transmembrane domains and membrane lipids. Because the site of sphingolipid synthesis overlaps the localization of IBV M, we asked whether perturbation of sphingolipids affected localization of IBV M. Short-term treatment with two inhibitors of sphingolipid synthesis had no effect on localization of IBV M or other Golgi markers. Thus, ongoing synthesis of these lipids was not required for proper localization. Surprisingly, a third inhibitor, d,l-threo-1-phenyl-2-decanoylamino-3-morpholino- 1-propanol (PDMP), shifted the steady-state distribution of IBV M from the Golgi complex to the ER. This effect was rapid and reversible and was also observed for ERGIC-53 but not for Golgi stack proteins. At the concentration of PDMP used, conversion of ceramide into both glucosylceramide and sphingomyelin was inhibited. Pretreatment with upstream inhibitors partially reversed the effects of PDMP, suggesting that ceramide accumulation mediates the PDMP-induced alterations. Indeed, an increase in cellular ceramide was measured in PDMP-treated cells. We propose that IBV M is at least in part localized by retrieval mechanisms. Further, ceramide accumulation reveals this cycle by upsetting the balance of anterograde and retrograde traffic and/ or disrupting retention by altering bilayer dynamics.


id: cord-323331-80d01l6f
title: Golgi Structure and Function in Health, Stress, and Diseases
author: Li, Jie
date: 2019-01-01
txt: ./txt/cord-323331-80d01l6f.txt
cache: ./cache/cord-323331-80d01l6f.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/31435807/
doi: 10.1007/978-3-030-23173-6_19
summary:
  Mechanistically, GRASP proteins form homodimers via the N-terminal PDZ domains, and dimers from adjacent Golgi cisternae further oligomerize in trans and function as the "glue" that tethers the cisternae into a stack (Wang et al. Other than the well-studied GRASP65-GM130 and GM130-p115-giantin complexes, the GRIP domain containing golgins are another group of proteins associated with the Golgi structure. Depletion of αSNAP in p53 null or Bax null cells still results in apoptosis, indicating that the anti-apoptotic function is independent of p53 and Bax. Interestingly, αSNAP depletion induces apoptosis independent of the cleavage of Golgi proteins such as GRASP65, golgin-160, and p115 but rather by dysregulation of ER-Golgi vesicle cycling and possibly through ER stress (Naydenov et al. The coiled-coil membrane protein golgin-84 is a novel rab effector required for Golgi ribbon formation Caspase-mediated cleavage of the stacking protein GRASP65 is required for Golgi fragmentation during apoptosis

abstract:
  The Golgi apparatus is a central intracellular membrane-bound organelle with key functions in trafficking, processing, and sorting of newly synthesized membrane and secretory proteins and lipids. To best perform these functions, Golgi membranes form a unique stacked structure. The Golgi structure is dynamic but tightly regulated; it undergoes rapid disassembly and reassembly during the cell cycle of mammalian cells and is disrupted under certain stress and pathological conditions. In the past decade, significant amount of effort has been made to reveal the molecular mechanisms that regulate the Golgi membrane architecture and function. Here we review the major discoveries in the mechanisms of Golgi structure formation, regulation, and alteration in relation to its functions in physiological and pathological conditions to further our understanding of Golgi structure and function in health and diseases.


id: cord-326015-ky4y2xjt
title: Protein sorting in the Golgi complex
author: Füllekrug, Joachim
date: 1998-08-14
txt: ./txt/cord-326015-ky4y2xjt.txt
cache: ./cache/cord-326015-ky4y2xjt.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/9714747/
doi: 10.1016/s0167-4889(98)00048-2
summary:
  In this review, we will discuss sorting of resident proteins in the Golgi complex mainly in the context of cisternal maturation [1, 2] . An essential feature of this maturation model is the prediction that Golgi resident proteins are more concentrated in retrograde vesicles than they are in the cisternae of the Golgi apparatus. This shows that Golgi resident enzymes do form gradients across the pathway and that these are unique to the particular protein. The surprising ¢nding that the membrane spanning domain (MSD) of Golgi residents su¤ced to localise reporter molecules to the appropriate part of the pathway suggested that this domain harboured important sorting information (for review, see [22] ). As this form of coatomer is found on Golgi associated transport vesicles [50] , COP I vesicles constitute RTCs. The presence of K(X)KXX or related signals on membrane proteins other than ER residents allows for the possibility that this motif also acts later in the pathway.

abstract:
  Even after one hundred years, the Golgi apparatus remains a major challenge in the field of Cell Biology. This is particularly true in terms of transport and of protein sorting. For example, the question how cargo proteins are transported through this organelle is still a matter of debate. Emphasis has been put on the role of anterograde and retrograde transport vesicles. These have been proposed to carry cargo from cisterna to cisterna and to recycle components needed for further rounds of transport. Alternatively, anterograde movement of cargo takes place in cisternal membranes rather than transport vesicles. These membranes assemble and mature in a cis to trans direction. In this case, retrograde transport vesicles need to recycle all components of the Golgi apparatus and this demands a highly dynamic and efficient sorting machinery. Here we will discuss possible mechanisms for protein sorting in the context of cisternal maturation and propose that a common mechanism is sufficient to explain both transport of cargo and sorting of resident proteins.


id: cord-328082-7c7slfbp
author: nan
date: 1993-03-02
txt: ./txt/cord-328082-7c7slfbp.txt
cache: ./cache/cord-328082-7c7slfbp.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/8449979/
doi: nan
summary:
  This caffeine-induced effect on the Golgi complex was different from that induced by BFA, since mannosidase II, a Golgi stack marker, remained perinuclearly located and the Golgi stack coat protein, beta-COP, was not detached from Golgi membranes in the presence of 10 mM caffeine at 20 degrees C. Further, caffeine at reduced temperature did not inhibit the retrograde movement of Golgi stack membranes observed in BFA-treated cells. In control cells, the glycoproteins were transported to the trans-Golgi region already at 200C as described earlier (Marlin and Simons, 1983; Saraste and Kuismanen, 1984) , and at higher temperatures increased labeling of the plasma membrane was observed (data not shown). Because of the effective inhibition of membrane traffic out of the ER at 20~ and the translocation of p58 to the periphery of the cell in the presence of caffeine, it was of great interest to study whether the morphology of the Golgi stack is affected under the conditions used.

title:
  Effect of caffeine and reduced temperature (20 degrees C) on the organization of the pre-Golgi and the Golgi stack membranes

abstract:
  In the present study we have dissected the transport pathways between the ER and the Golgi complex using a recently introduced (Kuismanen, E., J. Jantti, V. Makiranta, and M. Sariola. 1992. J. Cell Sci. 102:505- 513) inhibition of transport by caffeine at 20 degrees C. Recovery of the Golgi complex from brefeldin A (BFA) treatment was inhibited by caffeine at reduced temperature (20 degrees C) suggesting that caffeine inhibits the membrane traffic between the ER and the Golgi complex. Caffeine at 20 degrees C did not inhibit the BFA-induced retrograde movement of the Golgi membranes. Further, incubation of the cells in 10 mM caffeine at 20 degrees C had profound effects on the distribution and the organization of the pre-Golgi and the Golgi stack membranes. Caffeine treatment at 20 degrees C resulted in a selective and reversible translocation of the pre- and cis-Golgi marker protein (p58) to the periphery of the cell. This caffeine-induced effect on the Golgi complex was different from that induced by BFA, since mannosidase II, a Golgi stack marker, remained perinuclearly located and the Golgi stack coat protein, beta-COP, was not detached from Golgi membranes in the presence of 10 mM caffeine at 20 degrees C. Electron microscopic analysis showed that, in the presence of caffeine at 20 degrees C, the morphology of the Golgi stack was altered and accumulation of numerous small vesicles in the Golgi region was observed. The results in the present study suggest that caffeine at reduced temperature (20 degrees C) reveals a functional interface between the pre-Golgi and the Golgi stack.


id: cord-329515-ra20actc
author: nan
date: 1994-07-01
txt: ./txt/cord-329515-ra20actc.txt
cache: ./cache/cord-329515-ra20actc.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/8027183/
doi: nan
summary:
  Recently, oligomerization of a chimeric protein containing the first membrane-spanning domain of the M glycoprotein of avian coronavirus has been correlated to its retention in the Golgi apparatus (Weisz et al., 1993) . When COS cells transfected with this mutant were permeabilized, the predominant staining pattern was characteristic for the ER and the Golgi apparatus indicating that/,16-101,6-12A had lost p63wt localization (Fig. 6 c) . To further analyze the role of the cytoplasmic tail of p63 in retention and to determine whether the transmembrane and lumenal domains of this protein contribute to proper intracellular localization, we substituted each of these domains with the corresponding domains of the cell surface protein human DPPIV (Fig. 9) . A similar result was obtained with a construct that only contained the lumenal domain of p63 (DDP; DPPIV cytoplasmic; DPPIV transmembrane, p63 lumenal; Fig. 9 ) except that most of the ER staining was now replaced by cell surface expression (data not shown).

title:
  Retention of p63 in an ER-Golgi intermediate compartment depends on the presence of all three of its domains and on its ability to form oligomers

abstract:
  The type II membrane protein p63 is a resident protein of a membrane network interposed between rough ER and Golgi apparatus. To study the retention of p63, mutant forms were expressed in COS cells and the intracellular distribution determined by immunofluorescence microscopy. Investigation of chimeric constructs between p63 and the plasma membrane protein dipeptidylpeptidase IV showed that protein sequences from all three domains of the p63 protein are required to achieve complete intracellular retention. Mutational analysis of the 106-amino acid cytoplasmic tail of p63 revealed that the NH2-terminal 23 amino acids are necessary for retention. When p63 was solubilized with Triton X-100 and subjected to centrifugation at 100,000 g, it formed large, insoluble oligomers, particularly at neutral pH and below. A comparison of the behavior of wildtype and mutant p63 proteins in this assay revealed a perfect correlation between the formation of large oligomers and correct intracellular retention. These results suggest that self- association may be a major mechanism by which p63 is retained between the rough ER and the Golgi apparatus.


id: cord-329553-93tbgn2b
author: nan
date: 1992-04-02
txt: ./txt/cord-329553-93tbgn2b.txt
cache: ./cache/cord-329553-93tbgn2b.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/1560026/
doi: nan
summary:
  A series of experiments has shown that the 17-residue transmembrane domain of ST is sufficient to confer localization to the Golgi apparatus when transferred to the corresponding region of a cell surface type II integral membrane protein. In this report, we have fused different regions of the NH2-terminal ST sequence to the ectodomain of dipeptidyl peptidase IV (DPPIV), a type 11 surface membrane protein (Hong and Doyle, 1990; Ogato et al ., 1989) to study their abilities in conferring Golgi localization ofthe chimeric proteins. To determine the minimum sequence ofthe N112-terminal region of ST that is sufficient for membrane anchorage and Golgi localization, we have constructed a series of chimeric cDNAs which encode different fusion proteins ( Fig. 1 B) , with decreasing lengths of the N112-terminal ST sequence fused to the ectodomain of DPPIV .

title:
  The 17-residue transmembrane domain of beta-galactoside alpha 2,6- sialyltransferase is sufficient for Golgi retention

abstract:
  beta-Galactoside alpha 2,6-sialyltransferase (ST) is a type II integral membrane protein of the Golgi apparatus involved in the sialylation of N-linked glycans. A series of experiments has shown that the 17-residue transmembrane domain of ST is sufficient to confer localization to the Golgi apparatus when transferred to the corresponding region of a cell surface type II integral membrane protein. Lectin affinity chromatography of chimeric proteins bearing this 17-residue sequence suggests that these chimeric proteins are localized in the trans-Golgi cisternae and/or trans-Golgi network. Further experiments suggest that this 17-residue sequence functions as a retention signal for the Golgi apparatus.


id: cord-332484-qy8vj6uu
author: Pierini, Roberto
date: 2009-04-01
txt: ./txt/cord-332484-qy8vj6uu.txt
cache: ./cache/cord-332484-qy8vj6uu.txt
extension: .txt
mime: text/plain
url: https://doi.org/10.1016/j.semcdb.2009.03.015
doi: 10.1016/j.semcdb.2009.03.015
summary:
  This review describes examples where both intracellular bacteria (Salmonella, Chlamydia and Legionella) and viruses (picornaviruses and hepatitis C) recruit membrane vesicles to sites of replication by modulating proteins that control the secretory pathway. Intracellular bacteria remain within membrane-bound vacuoles to avoid delivery to lysosomes and then recruit vesicles from the secretory pathway to provide nutrients necessary for microbial growth and cell division. Many viruses generate densely packed membrane vesicles to shield them from recognition by cellular defence pathways that recognise double-stranded RNA, and at the same time the membranes provide a platform to recruit viral and host proteins required for replication [3] [4] [5] . This review describes how recent work on intracellular bacteria such as Salmonella, Chlamydia and Leigionella draws parallels with studies on (+) strand RNA viruses where microbial proteins recruit membranes by modulating proteins that control the secretory pathway.

title:
  Modulation of membrane traffic between endoplasmic reticulum, ERGIC and Golgi to generate compartments for the replication of bacteria and viruses

abstract:
  Several bacteria and viruses remodel cellular membranes to form compartments specialised for replication. Bacteria replicate within inclusions which recruit membrane vesicles from the secretory pathway to provide nutrients for microbial growth and division. Viruses generate densely packed membrane vesicles called viroplasm which provide a platform to recruit host and viral proteins necessary for replication. This review describes examples where both intracellular bacteria (Salmonella, Chlamydia and Legionella) and viruses (picornaviruses and hepatitis C) recruit membrane vesicles to sites of replication by modulating proteins that control the secretory pathway. In many cases this involves modulation of Rab and Arf GTPases.


id: cord-351964-hduv0ur4
author: nan
date: 1987-09-01
txt: ./txt/cord-351964-hduv0ur4.txt
cache: ./cache/cord-351964-hduv0ur4.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/2821011/
doi: nan
summary:
  The virus, which buds into pre-Golgi compartments, moves through the Golgi cisternae and exploits vesicles of the constitutive exocytic pathway of these fibroblastic hosts, which lack a regulated pathway, to reach the cell surface; the post-Golgi vesicles filled with progeny virions that can be seen near the cell surface apparently fuse with the plasma membrane to release the virus into the medium (for review see Dubois-Dalcq et al., 1984) . Condensation of secretory proteins and the formation of secretory granules of the regulated exocytic pathway occurs exclusively in the trans-Golgi network in uninfected AtT20 cells . B shows, near the lower surface of a cell growing on ECM, one of the extremely rare classes of post-Golgi transport vesicles which contain both virions (arrows) and a clump of condensed secretory protein that labels heavily with anti-ACTH antibody (arrowhead). In AtT20 cells, at 7-10-h postinfection with MHV-A59, both progeny virions and condensing secretory proteins accumulate in the trans-Golgi network.

title:
  Sorting of progeny coronavirus from condensed secretory proteins at the exit from the trans-Golgi network of AtT20 cells

abstract:
  Murine hepatitis virus (strain A59), (MHV-A59) is a coronavirus that buds into pre-Golgi compartments and then exploits the exocytic pathway of the host cell to reach the exterior. The fibroblastic cells in which replication of this virus is usually studied have only a constitutive exocytic pathway that the virus uses. MHV-A59 also infects, albeit inefficiently, AtT20 cells, murine pituitary tumor cells with a regulated as well as a constitutive exocytic pathway. Here we examine AtT20 cells at early times after the infection, when the Golgi apparatus retains its morphological and biochemical integrity. We observe that progeny coronavirus and secretory protein destined for the secretory granules of the regulated exocytic pathway traverse the same Golgi stacks and accumulate in the trans-Golgi network. Their pathways diverge at this site, the condensed secretory proteins including the ACTH going to the secretory granules and the coronavirus to post-Golgi transport vesicles devoid of ACTH. On very rare occasions there is missorting such that aggregates of condensed secretory proteins and viruses occur together in post-Golgi vesicles. We conclude that the constitutive and regulated exocytic pathways, identified respectively by the progeny virions and the secretory protein ACTH, diverge at the exit from the trans-Golgi network.


id: cord-352854-che3iwu3
author: Hart, Kristen C
date: 1997-12-18
txt: ./txt/cord-352854-che3iwu3.txt
cache: ./cache/cord-352854-che3iwu3.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/9050994/
doi: 10.1038/sj.onc.1200908
summary:
  However, when examined in focus formation assays, transformation of NIH3T3 cells were seen with derivatives of ras(61L) containing a mutated E1 targeting sequence that results in plasma membrane localization. These results demonstrate that: (1) activated ras targeted to Golgi membranes is unable to cause transformation; (2) lipid modifications at the C-terminus are not required for the transforming activity of plasma membrane-anchored ras(61L) derivatives, and serve primarily a targeting function; (3) a transmembrane domain can effectively substitute for C-terminal modifications that would normally target ras to the inner surface of the plasma membrane, indicating that ras(61L) does not need to reversibly dissociate from the membrane as might be allowed by the normal lipidation; and (4) in order to function properly, there exists a critical distance that the ras protein must reside from the plasma membrane.

title:
  Derivatives of activated H-ras lacking C-terminal lipid modifications retain transforming ability if targeted to the correct subcellular location

abstract:
  To examine the ability of ras to activate signal transduction pathways in the absence of lipid modifications, fusion proteins were constructed that target ras(WT) or activated ras(61L) to cellular membranes as integral membrane proteins, using the first transmembrane domain of the E1 protein of avian infectious bronchitis virus (IBV), which contains a cis-Golgi targeting signal. Golgi-targeted derivatives of activated ras were completely inactive in transformation assays. However, when examined in focus formation assays, transformation of NIH3T3 cells were seen with derivatives of ras(61L) containing a mutated E1 targeting sequence that results in plasma membrane localization. Removal of the lipid modification sites in and upstream of the CAAX motif did not abrogate the transforming activity of plasma membrane-localized ras(61L) derivatives, indicating that these lipid modifications are not essential for ras activity, as long as the protein is correctly localized to the plasma membrane. Interestingly, the activity of integral membrane versions of ras(61L) was strictly dependent on a minimum distance between the transmembrane domain anchor region and the coding sequence of ras. Derivatives with only a 3-amino acid linker were inactive, while linkers of either 11- or 22-amino acids were sufficient to restore transforming activity. These results demonstrate that: (1) activated ras targeted to Golgi membranes is unable to cause transformation; (2) lipid modifications at the C-terminus are not required for the transforming activity of plasma membrane-anchored ras(61L) derivatives, and serve primarily a targeting function; (3) a transmembrane domain can effectively substitute for C-terminal modifications that would normally target ras to the inner surface of the plasma membrane, indicating that ras(61L) does not need to reversibly dissociate from the membrane as might be allowed by the normal lipidation; and (4) in order to function properly, there exists a critical distance that the ras protein must reside from the plasma membrane.


id: cord-354726-b9xvycyk
title: Envelope glycoprotein interactions in coronavirus assembly
author: nan
date: 1995-10-02
txt: ./txt/cord-354726-b9xvycyk.txt
cache: ./cache/cord-354726-b9xvycyk.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/7593163/
doi: nan
summary:
  Using coimmunoprecipitation analysis we demonstrated that the M and S proteins of mouse hepatitis virus (MHV) interact specifically forming heteromultimeric complexes in infected cells. Yet, the self-association of the MHV envelope glycoproteins into higher order complexes is indicative of its role in the sorting of the viral membrane proteins and in driving the formation of the viral lipoprotein coat in virus assembly. Yet, the self-association of the MHV envelope glycoproteins into higher order complexes is indicative of its role in the sorting of the viral membrane proteins and in driving the formation of the viral lipoprotein coat in virus assembly. We have shown previously that neither of the envelope glycoproteins accumulates at the site of budding when expressed independently: the M protein alone localizes to the Golgi complex (Rottier and Rose, 1987; Krijnse Locker et al., 1992a; Klumperman et al., 1994) , whereas the S protein is transported to the plasma membrane (Vennema, H., and P.

abstract:
  Coronaviruses are assembled by budding into smooth membranes of the intermediate ER-to-Golgi compartment. We have studied the association of the viral membrane glycoproteins M and S in the formation of the virion envelope. Using coimmunoprecipitation analysis we demonstrated that the M and S proteins of mouse hepatitis virus (MHV) interact specifically forming heteromultimeric complexes in infected cells. These could be detected only when the detergents used for their solubilization from cells or virions were carefully chosen: a combination of nonionic (NP-40) and ionic (deoxycholic acid) detergents proved to be optimal. Pulse-chase experiments revealed that newly made M and S proteins engaged in complex formation with different kinetics. Whereas the M protein appeared in complexes immediately after its synthesis, newly synthesized S protein did so only after a lag phase of > 20 min. Newly made M was incorporated into virus particles faster than S, which suggests that it associates with preexisting S molecules. Using the vaccinia virus T7-driven coexpression of M and S we also demonstrate formation of M/S complexes in the absence of other coronaviral proteins. Pulse-chase labelings and coimmunoprecipitation analyses revealed that M and S associate in pre-Golgi membranes because the unglycosylated form of M appeared in M/S complexes rapidly. Since no association of M and S was detected when protein export from the ER was blocked by brefeldin A, stable complexes most likely arise in the ER-to-Golgi intermediate compartment. Sucrose velocity gradient analysis showed the M/S complexes to be heterogeneous and of higher order, suggesting that they are maintained by homo- and heterotypic interactions. M/S complexes colocalized with alpha-mannosidase II, a resident Golgi protein. They acquired Golgi-specific oligosaccharide modifications but were not detected at the cell surface. Thus, the S protein, which on itself was transported to the plasma membrane, was retained in the Golgi complex by its association with the M protein. Because coronaviruses bud at pre-Golgi membranes, this result implies that the envelope glycoprotein complexes do not determine the site of budding. Yet, the self-association of the MHV envelope glycoproteins into higher order complexes is indicative of its role in the sorting of the viral membrane proteins and in driving the formation of the viral lipoprotein coat in virus assembly.


id: cord-355580-4pv1zu1g
author: nan
date: 1992-06-01
txt: ./txt/cord-355580-4pv1zu1g.txt
cache: ./cache/cord-355580-4pv1zu1g.txt
extension: .txt
mime: text/plain
url: https://www.ncbi.nlm.nih.gov/pubmed/1577870/
doi: nan
summary:
  In the same cells, intact ribophorins I and II also underwent O-linked glycosylation in the presence of BFA, but these molecules were modified only during a short time period immediately after their synthesis was completed, and the modification affected only a fraction of the newly synthesized polypeptides. In the same cells, intact ribophorins I and II also underwent O-linked glycosylation in the presence of BFA, but these molecules were modified only during a short time period immediately after their synthesis was completed, and the modification affected only a fraction of the newly synthesized polypeptides. To determine whether the apparent increase in the molecular masses of the truncated ribophorin I molecules that appear in BFA-treated cells reflects a processing of the N-linked oligosaccharide chain, the effect of endo H treatment on this protein was examined.

title:
  O-glycosylation of intact and truncated ribophorins in brefeldin A- treated cells: newly synthesized intact ribophorins are only transiently accessible to the relocated glycosyltransferases

abstract:
  Ribophorins I and II are type I transmembrane glycoproteins of the ER that are segregated to the rough domains of this organelle. Both ribophorins appear to be part of the translocation apparatus for nascent polypeptides that is associated with membrane-bound ribosomes and participate in the formation of a proteinaceous network within the ER membrane that also includes other components of the translocation apparatus. The ribophorins are both highly stable proteins that lack O- linked sugars but each contains one high mannose N-linked oligosaccharide that remains endo H sensitive throughout their lifetimes. We have previously shown (Tsao, Y. S., N. E. Ivessa, M. Adesnik, D. D. Sabatini, and G. Kreibich. 1992. J. Cell Biol. 116:57- 67) that a COOH-terminally truncated variant of ribophorin I that contains only the first 332 amino acids of the luminal domain (RI332), when synthesized in permanent transformants of HeLa cells, undergoes a rapid degradation with biphasic kinetics in the ER itself and in a second, as yet unidentified nonlysosomal pre-Golgi compartment. We now show that in cells treated with brefeldin A (BFA) RI332 molecules undergo rapid O-glycosylation in a multistep process that involves the sequential addition of N-acetylgalactosamine, galactose, and terminal sialic acid residues. Addition of O-linked sugars affected all newly synthesized RI332 molecules and was completed soon after synthesis with a half time of about 10 min. In the same cells, intact ribophorins I and II also underwent O-linked glycosylation in the presence of BFA, but these molecules were modified only during a short time period immediately after their synthesis was completed, and the modification affected only a fraction of the newly synthesized polypeptides. More important, these molecules synthesized before the addition of BFA were not modified by O-glycosylation. The same is true for ribophorin I when overexpressed in HeLa cells although it is significantly less stable than the native polypeptide in control cells. We, therefore, conclude that soon after their synthesis, ribophorins lose their susceptibility to the relocated Golgi enzymes that effect the O-glycosylation, most likely as a consequence of a conformational change in the ribophorins that occurs during their maturation, although it cannot be excluded that rapid integration of these molecules into a supramolecular complex in the ER membrane leads to their inaccessibility to these enzymes.


