101
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Burguete AS, Fenn TD, Brunger AT, Pfeffer SR. Rab and Arl GTPase family members cooperate in the localization of the golgin GCC185. Cell 2008; 132:286-98. [PMID: 18243103 DOI: 10.1016/j.cell.2007.11.048] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2007] [Revised: 10/31/2007] [Accepted: 11/26/2007] [Indexed: 10/22/2022]
Abstract
GCC185 is a large coiled-coil protein at the trans Golgi network that is required for receipt of transport vesicles inbound from late endosomes and for anchoring noncentrosomal microtubules that emanate from the Golgi. Here, we demonstrate that recruitment of GCC185 to the Golgi is mediated by two Golgi-localized small GTPases of the Rab and Arl families. GCC185 binds Rab6, and mutation of residues needed for Rab binding abolishes Golgi localization. The crystal structure of Rab6 bound to the GCC185 Rab-binding domain reveals that Rab6 recognizes a two-fold symmetric surface on a coiled coil immediately adjacent to a C-terminal GRIP domain. Unexpectedly, Rab6 binding promotes association of Arl1 with the GRIP domain. We present a structure-derived model for dual GTPase membrane attachment that highlights the potential ability of Rab GTPases to reach binding partners at a significant distance from the membrane via their unstructured and membrane-anchored, hypervariable domains.
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102
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Role of the conserved oligomeric Golgi (COG) complex in protein glycosylation. Carbohydr Res 2008; 343:2024-31. [PMID: 18353293 DOI: 10.1016/j.carres.2008.01.034] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2007] [Revised: 01/23/2008] [Accepted: 01/24/2008] [Indexed: 11/20/2022]
Abstract
The Golgi apparatus is a central hub for both protein and lipid trafficking/sorting and is also a major site for glycosylation in the cell. This organelle employs a cohort of peripheral membrane proteins and protein complexes to keep its structural and functional organization. The conserved oligomeric Golgi (COG) complex is an evolutionary conserved peripheral membrane protein complex that is proposed to act as a retrograde vesicle tethering factor in intra-Golgi trafficking. The COG protein complex consists of eight subunits, distributed in two lobes, Lobe A (Cog1-4) and Lobe B (Cog5-8). Malfunctions in the COG complex have a significant impact on processes such as protein sorting, glycosylation, and Golgi integrity. A deletion of Lobe A COG subunits in yeasts causes severe growth defects while mutations in COG1, COG7, and COG8 in humans cause novel types of congenital disorders of glycosylation. These pathologies involve a change in structural Golgi phenotype and function. Recent results indicate that down-regulation of COG function results in the resident Golgi glycosyltransferases/glycosidases to be mislocalized or degraded.
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103
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Shestakova A, Suvorova E, Pavliv O, Khaidakova G, Lupashin V. Interaction of the conserved oligomeric Golgi complex with t-SNARE Syntaxin5a/Sed5 enhances intra-Golgi SNARE complex stability. ACTA ACUST UNITED AC 2008; 179:1179-92. [PMID: 18086915 PMCID: PMC2140037 DOI: 10.1083/jcb.200705145] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Tethering factors mediate initial interaction of transport vesicles with target membranes. Soluble N-ethylmaleimide–sensitive fusion protein attachment protein receptors (SNAREs) enable consequent docking and membrane fusion. We demonstrate that the vesicle tether conserved oligomeric Golgi (COG) complex colocalizes and coimmunoprecipitates with intra-Golgi SNARE molecules. In yeast cells, the COG complex preferentially interacts with the SNARE complexes containing yeast Golgi target (t)-SNARE Sed5p. In mammalian cells, hCog4p and hCog6p interact with Syntaxin5a, the mammalian homologue of Sed5p. Moreover, fluorescence resonance energy transfer reveals an in vivo interaction between Syntaxin5a and the COG complex. Knockdown of the mammalian COG complex decreases Golgi SNARE mobility, produces an accumulation of free Syntaxin5, and decreases the steady-state levels of the intra-Golgi SNARE complex. Finally, overexpression of the hCog4p N-terminal Syntaxin5a-binding domain destabilizes intra-Golgi SNARE complexes, disrupting the Golgi. These data suggest that the COG complex orchestrates vesicular trafficking similarly in yeast and mammalian cells by binding to the t-SNARE Syntaxin5a/Sed5p and enhancing the stability of intra-Golgi SNARE complexes.
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Affiliation(s)
- Anna Shestakova
- Department of Physiology and Biophysics, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
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104
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Bitto E, Bingman CA, Kondrashov DA, McCoy JG, Bannen RM, Wesenberg GE, Phillips GN. Structure and dynamics of gamma-SNAP: insight into flexibility of proteins from the SNAP family. Proteins 2008; 70:93-104. [PMID: 17634982 DOI: 10.1002/prot.21468] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Soluble N-ethylmaleimide-sensitive factor attachment protein gamma (gamma-SNAP) is a member of an eukaryotic protein family involved in intracellular membrane trafficking. The X-ray structure of Brachydanio rerio gamma-SNAP was determined to 2.6 A and revealed an all-helical protein comprised of an extended twisted-sheet of helical hairpins with a helical-bundle domain on its carboxy-terminal end. Structural and conformational differences between multiple observed gamma-SNAP molecules and Sec17, a SNAP family protein from yeast, are analyzed. Conformational variation in gamma-SNAP molecules is matched with great precision by the two lowest frequency normal modes of the structure. Comparison of the lowest-frequency modes from gamma-SNAP and Sec17 indicated that the structures share preferred directions of flexibility, corresponding to bending and twisting of the twisted sheet motif. We discuss possible consequences related to the flexibility of the SNAP proteins for the mechanism of the 20S complex disassembly during the SNAP receptors recycling.
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Affiliation(s)
- Eduard Bitto
- Center for Eukaryotic Structural Genomics, University of Wisconsin-Madison, Madison, Wisconsin 53706-1544, USA
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105
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Ishikura S, Koshkina A, Klip A. Small G proteins in insulin action: Rab and Rho families at the crossroads of signal transduction and GLUT4 vesicle traffic. Acta Physiol (Oxf) 2008; 192:61-74. [PMID: 18171430 DOI: 10.1111/j.1748-1716.2007.01778.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Insulin stimulates glucose uptake into muscle and adipose tissues through glucose transporter 4 (GLUT4). GLUT4 cycles between the intracellular compartments and the plasma membrane. GLUT4 traffic-regulating insulin signals are largely within the insulin receptor-insulin receptor substrate-phosphatidylinositol 3-kinase (IR-IRS-PI3K) axis. In muscle cells, insulin signal bifurcates downstream of the PI3K into one arm leading to the activation of the Ser/Thr kinases Akt and atypical protein kinase C, and another leading to the activation of Rho family protein Rac1 leading to actin remodelling. Activated Akt inactivates AS160, a GTPase-activating protein for Rab family small G proteins. Here we review the roles of Rab and Rho proteins, particularly Rab substrates of AS160 and Rac1, in insulin-stimulated GLUT4 traffic. We discuss: (1) how distinct steps in GLUT4 traffic may be regulated by discrete Rab proteins, and (2) the importance of Rac1 activation in insulin-induced actin remodelling in muscle cells, a key element for the net gain in surface GLUT4.
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Affiliation(s)
- S Ishikura
- Program in Cell Biology, The Hospital for Sick Children, Toronto, ON, Canada
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106
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Kornhuber J, Tripal P, Reichel M, Terfloth L, Bleich S, Wiltfang J, Gulbins E. Identification of New Functional Inhibitors of Acid Sphingomyelinase Using a Structure−Property−Activity Relation Model. J Med Chem 2007; 51:219-37. [DOI: 10.1021/jm070524a] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Johannes Kornhuber
- Department of Psychiatry and Psychotherapy, University of Erlangen, Germany, Molecular Networks, Erlangen, Germany, and Department of Molecular Biology, University of Duisburg—Essen, Germany
| | - Philipp Tripal
- Department of Psychiatry and Psychotherapy, University of Erlangen, Germany, Molecular Networks, Erlangen, Germany, and Department of Molecular Biology, University of Duisburg—Essen, Germany
| | - Martin Reichel
- Department of Psychiatry and Psychotherapy, University of Erlangen, Germany, Molecular Networks, Erlangen, Germany, and Department of Molecular Biology, University of Duisburg—Essen, Germany
| | - Lothar Terfloth
- Department of Psychiatry and Psychotherapy, University of Erlangen, Germany, Molecular Networks, Erlangen, Germany, and Department of Molecular Biology, University of Duisburg—Essen, Germany
| | - Stefan Bleich
- Department of Psychiatry and Psychotherapy, University of Erlangen, Germany, Molecular Networks, Erlangen, Germany, and Department of Molecular Biology, University of Duisburg—Essen, Germany
| | - Jens Wiltfang
- Department of Psychiatry and Psychotherapy, University of Erlangen, Germany, Molecular Networks, Erlangen, Germany, and Department of Molecular Biology, University of Duisburg—Essen, Germany
| | - Erich Gulbins
- Department of Psychiatry and Psychotherapy, University of Erlangen, Germany, Molecular Networks, Erlangen, Germany, and Department of Molecular Biology, University of Duisburg—Essen, Germany
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107
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Swennen D, Beckerich JM. Yarrowia lipolytica vesicle-mediated protein transport pathways. BMC Evol Biol 2007; 7:219. [PMID: 17997821 PMCID: PMC2241642 DOI: 10.1186/1471-2148-7-219] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2007] [Accepted: 11/12/2007] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND Protein secretion is a universal cellular process involving vesicles which bud and fuse between organelles to bring proteins to their final destination. Vesicle budding is mediated by protein coats; vesicle targeting and fusion depend on Rab GTPase, tethering factors and SNARE complexes. The Génolevures II sequencing project made available entire genome sequences of four hemiascomycetous yeasts, Yarrowia lipolytica, Debaryomyces hansenii, Kluyveromyces lactis and Candida glabrata. Y. lipolytica is a dimorphic yeast and has good capacities to secrete proteins. The translocation of nascent protein through the endoplasmic reticulum membrane was well studied in Y. lipolytica and is largely co-translational as in the mammalian protein secretion pathway. RESULTS We identified S. cerevisiae proteins involved in vesicular secretion and these protein sequences were used for the BLAST searches against Génolevures protein database (Y. lipolytica, C. glabrata, K. lactis and D. hansenii). These proteins are well conserved between these yeasts and Saccharomyces cerevisiae. We note several specificities of Y. lipolytica which may be related to its good protein secretion capacities and to its dimorphic aspect. An expansion of the Y. lipolytica Rab protein family was observed with autoBLAST and the Rab2- and Rab4-related members were identified with BLAST against NCBI protein database. An expansion of this family is also found in filamentous fungi and may reflect the greater complexity of the Y. lipolytica secretion pathway. The Rab4p-related protein may play a role in membrane recycling as rab4 deleted strain shows a modification of colony morphology, dimorphic transition and permeability. Similarly, we find three copies of the gene (SSO) encoding the plasma membrane SNARE protein. Quantification of the percentages of proteins with the greatest homology between S. cerevisiae, Y. lipolytica and animal homologues involved in vesicular transport shows that 40% of Y. lipolytica proteins are closer to animal ones, whereas they are only 13% in the case of S. cerevisiae. CONCLUSION These results provide further support for the idea, previously noted about the endoplasmic reticulum translocation pathway, that Y. lipolytica is more representative of vesicular secretion of animals and other fungi than is S. cerevisiae.
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Affiliation(s)
- Dominique Swennen
- Laboratoire de Microbiologie et Génétique Moléculaire INRA-CNRS-AgroParisTech UMR 1238 CBAI BP01 F-78850 Thiverval Grignon, France.
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108
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Abstract
Remarkable strides have been made over the past 20 years in elucidating the molecular basis of membrane trafficking. Indeed, a combination of biochemical and genetic approaches have determined the identity and function of many of the core constituents needed for protein secretion and endocytosis. But much remains to be learned. This review highlights underlying themes in membrane traffic to help us refocus and solve many remaining and newly emerging issues that are fundamental to mammalian cell biology and human physiology.
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Affiliation(s)
- Suzanne R Pfeffer
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305-5307, USA.
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109
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Sun Y, Shestakova A, Hunt L, Sehgal S, Lupashin V, Storrie B. Rab6 regulates both ZW10/RINT-1 and conserved oligomeric Golgi complex-dependent Golgi trafficking and homeostasis. Mol Biol Cell 2007; 18:4129-42. [PMID: 17699596 PMCID: PMC1995728 DOI: 10.1091/mbc.e07-01-0080] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We used multiple approaches to investigate the role of Rab6 relative to Zeste White 10 (ZW10), a mitotic checkpoint protein implicated in Golgi/endoplasmic reticulum (ER) trafficking/transport, and conserved oligomeric Golgi (COG) complex, a putative tether in retrograde, intra-Golgi trafficking. ZW10 depletion resulted in a central, disconnected cluster of Golgi elements and inhibition of ERGIC53 and Golgi enzyme recycling to ER. Small interfering RNA (siRNA) against RINT-1, a protein linker between ZW10 and the ER soluble N-ethylmaleimide-sensitive factor attachment protein receptor, syntaxin 18, produced similar Golgi disruption. COG3 depletion fragmented the Golgi and produced vesicles; vesicle formation was unaffected by codepletion of ZW10 along with COG, suggesting ZW10 and COG act separately. Rab6 depletion did not significantly affect Golgi ribbon organization. Epistatic depletion of Rab6 inhibited the Golgi-disruptive effects of ZW10/RINT-1 siRNA or COG inactivation by siRNA or antibodies. Dominant-negative expression of guanosine diphosphate-Rab6 suppressed ZW10 knockdown induced-Golgi disruption. No cross-talk was observed between Rab6 and endosomal Rab5, and Rab6 depletion failed to suppress p115 (anterograde tether) knockdown-induced Golgi disruption. Dominant-negative expression of a C-terminal fragment of Bicaudal D, a linker between Rab6 and dynactin/dynein, suppressed ZW10, but not COG, knockdown-induced Golgi disruption. We conclude that Rab6 regulates distinct Golgi trafficking pathways involving two separate protein complexes: ZW10/RINT-1 and COG.
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Affiliation(s)
- Yi Sun
- Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205
| | - Anna Shestakova
- Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205
| | - Lauren Hunt
- Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205
| | - Siddharth Sehgal
- Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205
| | - Vladimir Lupashin
- Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205
| | - Brian Storrie
- Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205
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110
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Wiseman RL, Koulov A, Powers E, Kelly JW, Balch WE. Protein energetics in maturation of the early secretory pathway. Curr Opin Cell Biol 2007; 19:359-67. [PMID: 17686625 PMCID: PMC2094714 DOI: 10.1016/j.ceb.2007.05.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 05/23/2007] [Accepted: 05/29/2007] [Indexed: 01/26/2023]
Abstract
The early secretory pathway (ESP) consisting of the endoplasmic reticulum (ER), pre-Golgi intermediates and the Golgi stack links protein synthesis to folding and vesicle trafficking to generate the membrane architecture of the eukaryotic cell. The fundamental principles that contribute to organization of the ESP remain largely unknown. We raise the possibility that assembly of the ESP is largely built on a foundation that is influenced by the kinetic and thermodynamic properties of the protein fold. Folding energetics may provide an adjustable platform for adaptor-dependent interactions with the transport machinery, suggesting the possibility that protein cargo energetics plays a central role in directing both trafficking patterns and global compartmental organization of the ESP. In this view, cargo energetics likely coordinates the composition and maturation of ER and Golgi compartments with the physiological state of the cell in different tissue and environmental settings.
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Affiliation(s)
- R Luke Wiseman
- The Scripps Research Institute, Department of Chemistry, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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111
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Cavanaugh LF, Chen X, Richardson BC, Ungar D, Pelczer I, Rizo J, Hughson FM. Structural analysis of conserved oligomeric Golgi complex subunit 2. J Biol Chem 2007; 282:23418-26. [PMID: 17565980 DOI: 10.1074/jbc.m703716200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The conserved oligomeric Golgi (COG) complex is strongly implicated in retrograde vesicular trafficking within the Golgi apparatus. Although its mechanism of action is poorly understood, it has been proposed to function by mediating the initial physical contact between transport vesicles and their membrane targets. An analogous role in tethering vesicles has been suggested for at least six additional large multisubunit complexes, including the exocyst, a complex essential for trafficking to the plasma membrane. Here we report the solution structure of a large portion of yeast Cog2p, one of eight subunits composing the COG complex. The structure reveals a six-helix bundle with few conserved surface features but a general resemblance to recently determined crystal structures of four different exocyst subunits. This finding provides the first structural evidence that COG, like the exocyst and potentially other tethering complexes, is constructed from helical bundles. These structures may represent platforms for interaction with other trafficking proteins including SNAREs (soluble N-ethylmaleimide factor attachment protein receptors) and Rabs.
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Affiliation(s)
- Lorraine F Cavanaugh
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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112
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Cai H, Reinisch K, Ferro-Novick S. Coats, tethers, Rabs, and SNAREs work together to mediate the intracellular destination of a transport vesicle. Dev Cell 2007; 12:671-82. [PMID: 17488620 DOI: 10.1016/j.devcel.2007.04.005] [Citation(s) in RCA: 501] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Tethering factors have been shown to interact with Rabs and SNAREs and, more recently, with coat proteins. Coat proteins are required for cargo selection and membrane deformation to bud a transport vesicle from a donor compartment. It was once thought that a vesicle must uncoat before it recognizes its target membrane. However, recent findings have revealed a role for the coat in directing a vesicle to its correct intracellular destination. In this review we will discuss the literature that links coat proteins to vesicle targeting events.
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Affiliation(s)
- Huaqing Cai
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06519, USA
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113
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Stockert RJ, Potvin B, Nath S, Wolkoff AW, Stanley P. New liver cell mutants defective in the endocytic pathway. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1741-9. [PMID: 17512493 PMCID: PMC1939891 DOI: 10.1016/j.bbamem.2007.04.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Revised: 03/06/2007] [Accepted: 04/02/2007] [Indexed: 11/17/2022]
Abstract
To isolate mutant liver cells defective in the endocytic pathway, a selection strategy using toxic ligands for two distinct membrane receptors was utilized. Rare survivors termed trafficking mutants (Trf2-Trf7) were stable and more resistant than the parental HuH-7 cells to both toxin conjugates. They differed from the previously isolated Trf1 HuH-7 mutant as they expressed casein kinase 2 alpha'' (CK2alpha'') which is missing from Trf1 cells and which corrects the Trf1 trafficking phenotype. Binding of (125)I-asialoorosomucoid (ASOR) and cell surface expression of asialoglycoprotein receptor (ASGPR) were reduced approximately 20%-60% in Trf2-Trf7 cells compared to parental HuH-7, without a reduction in total cellular ASGPR. Based on (125)I-transferrin binding, cell surface transferrin receptor activity was reduced between 13% and 88% in the various mutant cell lines. Distinctive phenotypic traits were identified in the differential resistance of Trf2-Trf7 to a panel of lectins and toxins and to UV light-induced cell death. By following the endocytic uptake and trafficking of Alexa(488)-ASOR, significant differences in endosomal fusion between parental HuH-7 and the Trf mutants became apparent. Unlike parental HuH-7 cells in which the fusion of endosomes into larger vesicles was evident as early as 20 min, ASOR endocytosed into the Trf mutants remained within small vesicles for up to 60 min. Identifying the biochemical and genetic mechanisms underlying these phenotypes should uncover novel and unpredicted protein-protein or protein-lipid interactions that orchestrate specific steps in membrane protein trafficking.
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Affiliation(s)
- Richard J Stockert
- The Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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114
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Sehgal PB, Mukhopadhyay S. Pulmonary arterial hypertension: a disease of tethers, SNAREs and SNAPs? Am J Physiol Heart Circ Physiol 2007; 293:H77-85. [PMID: 17416597 DOI: 10.1152/ajpheart.01386.2006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Histological and electron microscopic studies over the past four decades have highlighted "plump," "enlarged" endothelial, smooth muscle, and fibroblastic cellular elements with increased endoplasmic reticulum, Golgi stacks, and vacuolation in pulmonary arterial lesions in human and in experimental (hypoxia and monocrotaline) pulmonary arterial hypertension. However, the contribution of disrupted intracellular membrane trafficking in the pathobiology of this disease has received insufficient attention. Recent studies suggest a pathogenetic role of the disruption of intracellular trafficking of vasorelevant proteins and cell-surface receptors in the development of this disease. The purpose of this essay is to highlight the molecular regulation of vesicular trafficking by membrane tethers, SNAREs and SNAPs, and to suggest how their dysfunction, directly and/or indirectly, might contribute to development of pulmonary arterial hypertension in experimental models and in humans, including that due to mutations in bone morphogenetic receptor type 2.
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Affiliation(s)
- Pravin B Sehgal
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, NY 10595, USA.
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115
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116
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Abstract
Transport vesicles must dock with the appropriate acceptor membrane to ensure faithful protein delivery. Recent work identifies some of the molecular mechanisms that contribute to the specificity of this reaction.
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117
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Sehgal PB, Mukhopadhyay S. Dysfunctional intracellular trafficking in the pathobiology of pulmonary arterial hypertension. Am J Respir Cell Mol Biol 2007; 37:31-7. [PMID: 17363775 PMCID: PMC1899345 DOI: 10.1165/rcmb.2007-0066tr] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Discussions of the initiation of pulmonary arterial hypertension (PAH) in man and in experimental models have centered around intimal and medial proliferation in medium-sized pulmonary arteries. The histologic events are thought to include disordered proliferation of enlarged, vacuolated endothelial cells, neo-muscularization of the affected blood vessels, and vascular pruning. The discovery of the association of familial and sporadic PAH with mutations in BMPR2 has generated intense interest in cytokine receptor trafficking and function in the endothelial cell and how this might be disrupted to yield an enlarged proliferative cell phenotype. Nevertheless, considerations of the subcellular machinery of membrane trafficking in the endothelial cell and consequences of the disruption of this outward and inward membrane trafficking are largely absent from discussions of the pathobiology of PAH. Long-standing electron microscopy data in the PAH field has demonstrated marked disruptions of intracellular membrane trafficking in human and experimental PAH. Further, a role of the membrane-trafficking regulator Nef in simian HIV-induced PAH in macaques and in HIV-induced PAH in man is now evident. Additionally, monocrotaline and hypoxia are known to disrupt the function of Golgi tethers, SNAREs, SNAPs, and N-ethylmaleimide-sensitive factor ("the Golgi blockade hypothesis"). These results, along with recent reports demonstrating the trapping of PAH-associated human BMPR2 mutants in the Golgi, highlight the implications of disrupted intracellular membrane trafficking in the pathobiology of PAH. The purpose of this review is to present a brief overview of the molecular basis of intracellular trafficking and relate these considerations to the pathobiology of PAH.
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Affiliation(s)
- Pravin B Sehgal
- Basic Sciences Building, Department of Cell Biology & Anatomy, New York Medical College, Valhalla, NY 10595, USA.
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118
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Huang S, Lifshitz LM, Jones C, Bellve KD, Standley C, Fonseca S, Corvera S, Fogarty KE, Czech MP. Insulin stimulates membrane fusion and GLUT4 accumulation in clathrin coats on adipocyte plasma membranes. Mol Cell Biol 2007; 27:3456-69. [PMID: 17339344 PMCID: PMC1899973 DOI: 10.1128/mcb.01719-06] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Total internal reflection fluorescence (TIRF) microscopy reveals highly mobile structures containing enhanced green fluorescent protein-tagged glucose transporter 4 (GLUT4) within a zone about 100 nm beneath the plasma membrane of 3T3-L1 adipocytes. We developed a computer program (Fusion Assistant) that enables direct analysis of the docking/fusion kinetics of hundreds of exocytic fusion events. Insulin stimulation increases the fusion frequency of exocytic GLUT4 vesicles by approximately 4-fold, increasing GLUT4 content in the plasma membrane. Remarkably, insulin signaling modulates the kinetics of the fusion process, decreasing the vesicle tethering/docking duration prior to membrane fusion. In contrast, the kinetics of GLUT4 molecules spreading out in the plasma membrane from exocytic fusion sites is unchanged by insulin. As GLUT4 accumulates in the plasma membrane, it is also immobilized in punctate structures on the cell surface. A previous report suggested these structures are exocytic fusion sites (Lizunov et al., J. Cell Biol. 169:481-489, 2005). However, two-color TIRF microscopy using fluorescent proteins fused to clathrin light chain or GLUT4 reveals these structures are clathrin-coated patches. Taken together, these data show that insulin signaling accelerates the transition from docking of GLUT4-containing vesicles to their fusion with the plasma membrane and promotes GLUT4 accumulation in clathrin-based endocytic structures on the plasma membrane.
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Affiliation(s)
- Shaohui Huang
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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119
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Control systems for membrane fusion in the ancestral eukaryote; evolution of tethering complexes and SM proteins. BMC Evol Biol 2007; 7:29. [PMID: 17319956 PMCID: PMC1810245 DOI: 10.1186/1471-2148-7-29] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2006] [Accepted: 02/23/2007] [Indexed: 12/31/2022] Open
Abstract
Background In membrane trafficking, the mechanisms ensuring vesicle fusion specificity remain to be fully elucidated. Early models proposed that specificity was encoded entirely by SNARE proteins; more recent models include contributions from Rab proteins, Syntaxin-binding (SM) proteins and tethering factors. Most information on membrane trafficking derives from an evolutionarily narrow sampling of model organisms. However, considering factors from a wider diversity of eukaryotes can provide both functional information on core systems and insight into the evolutionary history of the trafficking machinery. For example, the major Qa/syntaxin SNARE families are present in most eukaryotic genomes and likely each evolved via gene duplication from a single ancestral syntaxin before the existing eukaryotic groups diversified. This pattern is also likely for Rabs and various other components of the membrane trafficking machinery. Results We performed comparative genomic and phylogenetic analyses, when relevant, on the SM proteins and components of the tethering complexes, both thought to contribute to vesicle fusion specificity. Despite evidence suggestive of secondary losses amongst many lineages, the tethering complexes are well represented across the eukaryotes, suggesting an origin predating the radiation of eukaryotic lineages. Further, whilst we detect distant sequence relations between GARP, COG, exocyst and DSL1 components, these similarities most likely reflect convergent evolution of similar secondary structural elements. No similarity is found between the TRAPP and HOPS complexes and the other tethering factors. Overall, our data favour independent origins for the various tethering complexes. The taxa examined possess at least one homologue of each of the four SM protein families; since the four monophyletic families each encompass a wide diversity of eukaryotes, the SM protein families very likely evolved before the last common eukaryotic ancestor (LCEA). Conclusion These data further support a highly complex LCEA and indicate that the basic architecture of the trafficking system is remarkably conserved and ancient, with the SM proteins and tethering factors having originated very early in eukaryotic evolution. However, the independent origin of the tethering complexes suggests a novel pattern for increasing complexity in the membrane trafficking system, in addition to the pattern of paralogous machinery elaboration seen thus far.
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Abstract
Fusion controls mitochondrial morphology and is important for normal mitochondrial function, including roles in respiration, development, and apoptosis. Key components of the mitochondrial fusion machinery have been identified, allowing an initial dissection of its molecular mechanism. Outer and inner membrane fusion events are coordinately coupled but are mechanistically distinct. Mitofusins are mitochondrial GTPases that likely mediate outer membrane fusion. The dynamin-related protein OPA1/Mgm1p is required for inner membrane fusion and maintenance of normal cristae structure. We highlight recent findings that have advanced our understanding of the mechanism, function, and regulation of mitochondrial fusion.
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Affiliation(s)
| | - David C. Chan
- Contact information: California Institute of Technology, Division of Biology, MC114-96, Pasadena, CA 91125, Tel: (626) 395-2670, Fax: (626) 395-8826,
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121
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Stow JL, Manderson AP, Murray RZ. SNAREing immunity: the role of SNAREs in the immune system. Nat Rev Immunol 2007; 6:919-29. [PMID: 17124513 DOI: 10.1038/nri1980] [Citation(s) in RCA: 183] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The trafficking of molecules and membranes within cells is a prerequisite for all aspects of cellular immune functions, including the delivery and recycling of cell-surface proteins, secretion of immune mediators, ingestion of pathogens and activation of lymphocytes. SNARE (soluble-N-ethylmaleimide-sensitive-factor accessory-protein receptor)-family members mediate membrane fusion during all steps of trafficking, and function in almost all aspects of innate and adaptive immune responses. Here, we provide an overview of the roles of SNAREs in immune cells, offering insight into one level at which precision and tight regulation are instilled on immune responses.
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Affiliation(s)
- Jennifer L Stow
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
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122
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Latijnhouwers M, Gillespie T, Boevink P, Kriechbaumer V, Hawes C, Carvalho CM. Localization and domain characterization of Arabidopsis golgin candidates. JOURNAL OF EXPERIMENTAL BOTANY 2007; 58:4373-4386. [PMID: 18182439 DOI: 10.1093/jxb/erm304] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Golgins are large coiled-coil proteins that play a role in tethering of vesicles to Golgi membranes and in maintaining the overall structure of the Golgi apparatus. Six Arabidopsis proteins with the structural characteristics of golgins were isolated and shown to locate to Golgi stacks when fused to GFP. Two of these golgin candidates (GC1 and GC2) possess C-terminal transmembrane (TM) domains with similarity to the TM domain of human golgin-84. The C-termini of two others (GC3/GDAP1 and GC4) contain conserved GRAB and GA1 domains that are also found in yeast Rud3p and human GMAP210. GC5 shares similarity with yeast Sgm1p and human TMF and GC6 with yeast Uso1p and human p115. When fused to GFP, the C-terminal domains of AtCASP and GC1 to GC6 localized to the Golgi, showing that they contain Golgi localization motifs. The N-termini, on the other hand, label the cytosol or nucleus. Immuno-gold labelling and co-expression with the cis Golgi Q-SNARE Memb11 resulted in a more detailed picture of the sub-Golgi location of some of these putative golgins. Using two independent assays it is further demonstrated that the interaction between GC5, the TMF homologue, and the Rab6 homologues is conserved in plants.
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Affiliation(s)
- Maita Latijnhouwers
- Plant Pathology Programme, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK
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123
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Gürkan C, Stagg SM, Lapointe P, Balch WE. The COPII cage: unifying principles of vesicle coat assembly. Nat Rev Mol Cell Biol 2006; 7:727-38. [PMID: 16990852 DOI: 10.1038/nrm2025] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Communication between compartments of the exocytic and endocytic pathways in eukaryotic cells involves transport carriers - vesicles and tubules - that mediate the vectorial movement of cargo. Recent studies of transport-carrier formation in the early secretory pathway have provided new insights into the mechanisms of cargo selection by coat protein complex-II (COPII) adaptor proteins, the construction of cage-protein scaffolds and fission. These studies are beginning to produce a unifying molecular and structural model of coat function in the formation and fission of vesicles and tubules in endomembrane traffic.
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Affiliation(s)
- Cemal Gürkan
- Department of Electron Microscopy and Molecular Pathology, the Cyprus Institute of Neurology and Genetics, International Airport Avenue #6, Agios Dometios, 1683, Nicosia, Cyprus
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124
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Abstract
Productive viral infection is dependent upon post-entry migration of viruses/viral components to sites within a host cell that complement viral deficiencies. Delivery of virions or component proteins to appropriate sites within an infected cell is critical for completing successive stages in viral replication, including release into the cytoplasm, uncoating, genome replication, viral gene expression, assembly and budding. Vesicular transport is essential for steady-state cellular trafficking of membrane-associated proteins. Rab GTPases and their associated effectors are key regulators of vesicular transport pathways. In recent years, Rab proteins have been implicated in the endocytic or exocytic sorting of component viral proteins or intact viruses, most of which are known to be membrane-encapsulated and enveloped. This review will discuss the current understanding of how Rab GTPases and their effectors may regulate individual vesicular transport steps, and detail emerging discoveries examining how specific Rabs and effectors support viral replication.
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Affiliation(s)
- Thomas W Hodge
- University of Georgia, College of Veterinary Medicine, Department of Infectious Diseases, Athens, GA 30602, USA, and, Hudson–Alpha Institute for Biotechnology Investigator, Huntsville, AL, USA
| | - James L Murray
- University of Georgia, Animal Health Research Center, 111 Carlton Street, Room 113, Athens, GA 30602, USA
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125
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Béthune J, Wieland F, Moelleken J. COPI-mediated Transport. J Membr Biol 2006; 211:65-79. [PMID: 17041781 DOI: 10.1007/s00232-006-0859-7] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2005] [Revised: 03/18/2006] [Indexed: 12/27/2022]
Abstract
COPI-coated vesicles are protein and liquid carriers that mediate transport within the early secretory pathway. In this Topical Review, we present their main protein components and discuss current models for cargo sorting. Finally, we describe the striking similarities that exist between the COPI system and the two other characterized types of vesicular carriers: COPII- and clathrin-coated vesicles.
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Affiliation(s)
- J Béthune
- Biochemie Zentrum, University of Heidelberg, Im Neuenheimer Feld 328, D-69120, Heidelberg, Germany.
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126
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Besteiro S, Coombs GH, Mottram JC. The SNARE protein family of Leishmania major. BMC Genomics 2006; 7:250. [PMID: 17026746 PMCID: PMC1626469 DOI: 10.1186/1471-2164-7-250] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Accepted: 10/06/2006] [Indexed: 11/21/2022] Open
Abstract
Background Leishmania major is a protozoan parasite with a highly polarised cell shape that depends upon endocytosis and exocytosis from a single area of the plasma membrane, the flagellar pocket. SNAREs (soluble N-ethylmaleimide-sensitive factor adaptor proteins receptors) are key components of the intracellular vesicle-mediated transports that take place in all eukaryotic cells. They are membrane-bound proteins that facilitate the docking and fusion of vesicles with organelles. The recent availability of the genome sequence of L. major has allowed us to assess the complement of SNAREs in the parasite and to investigate their location in comparison with metazoans. Results Bioinformatic searches of the L. major genome revealed a total of 27 SNARE domain-containing proteins that could be classified in structural groups by phylogenetic analysis. 25 of these possessed the expected features of functional SNAREs, whereas the other two could represent kinetoplastid-specific proteins that might act as regulators of the SNARE complexes. Other differences of Leishmania SNAREs were the absence of double SNARE domain-containing and of the brevin classes of these proteins. Members of the Qa group of Leishmania SNAREs showed differential expressions profiles in the two main parasite forms whereas their GFP-tagging and in vivo expression revealed localisations in the Golgi, late endosome/lysosome and near the flagellar pocket. Conclusion The early-branching eukaryote L. major apparently possess a SNARE repertoire that equals in number the one of metazoans such as Drosophila, showing that the machinery for vesicle fusion is well conserved throughout the eukaryotes. However, the analysis revealed the absence of certain types of SNAREs found in metazoans and yeast, while suggesting the presence of original SNAREs as well as others with unusual localisation. This study also presented the intracellular localisation of the L. major SNAREs from the Qa group and reveals that these proteins could be useful as organelle markers in this parasitic protozoon.
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Affiliation(s)
- Sébastien Besteiro
- Wellcome Centre for Molecular Parasitology and Division of Infection & Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, G12 8TA, UK
| | - Graham H Coombs
- Wellcome Centre for Molecular Parasitology and Division of Infection & Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, G12 8TA, UK
| | - Jeremy C Mottram
- Wellcome Centre for Molecular Parasitology and Division of Infection & Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, G12 8TA, UK
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127
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Bonifacino JS, Rojas R. Retrograde transport from endosomes to the trans-Golgi network. Nat Rev Mol Cell Biol 2006; 7:568-79. [PMID: 16936697 DOI: 10.1038/nrm1985] [Citation(s) in RCA: 486] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A subset of intracellular transmembrane proteins such as acid-hydrolase receptors, processing peptidases and SNAREs, as well as extracellular protein toxins such as Shiga toxin and ricin, undergoes 'retrograde' transport from endosomes to the trans-Golgi network. Here, we discuss recent studies that have begun to unravel the molecular machinery that is involved in this process. We also propose a central role for a 'tubular endosomal network' in sorting to recycling pathways that lead not only to the trans-Golgi network but also to different plasma-membrane domains and to specialized storage vesicles.
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Affiliation(s)
- Juan S Bonifacino
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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128
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Yu S, Satoh A, Pypaert M, Mullen K, Hay JC, Ferro-Novick S. mBet3p is required for homotypic COPII vesicle tethering in mammalian cells. ACTA ACUST UNITED AC 2006; 174:359-68. [PMID: 16880271 PMCID: PMC2064232 DOI: 10.1083/jcb.200603044] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
TRAPPI is a large complex that mediates the tethering of COPII vesicles to the Golgi (heterotypic tethering) in the yeast Saccharomyces cerevisiae. In mammalian cells, COPII vesicles derived from the transitional endoplasmic reticulum (tER) do not tether directly to the Golgi, instead, they appear to tether to each other (homotypic tethering) to form vesicular tubular clusters (VTCs). We show that mammalian Bet3p (mBet3p), which is the most highly conserved TRAPP subunit, resides on the tER and adjacent VTCs. The inactivation of mBet3p results in the accumulation of cargo in membranes that colocalize with the COPII coat. Furthermore, using an assay that reconstitutes VTC biogenesis in vitro, we demonstrate that mBet3p is required for the tethering and fusion of COPII vesicles to each other. Consistent with the proposal that mBet3p is required for VTC biogenesis, we find that ERGIC-53 (VTC marker) and Golgi architecture are disrupted in siRNA-treated mBet3p-depleted cells. These findings imply that the TRAPPI complex is essential for VTC biogenesis.
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Affiliation(s)
- Sidney Yu
- Howard Hughes Medical Institute and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06519, USA
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129
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Hofmann KP, Spahn CMT, Heinrich R, Heinemann U. Building functional modules from molecular interactions. Trends Biochem Sci 2006; 31:497-508. [PMID: 16890441 DOI: 10.1016/j.tibs.2006.07.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Revised: 06/01/2006] [Accepted: 07/20/2006] [Indexed: 10/24/2022]
Abstract
The main reaction pathways in the living cell are carried out by functional modules--namely, macromolecular machines with compact structure or ensembles that change their composition and/or organization during function. Modules define themselves by spatial sequestration, chemical specificity and a characteristic time domain within which their function proceeds. On receiving a specific input, modules go through functional cycles, with phases of increasing and decreasing complexity of molecular interactions. Here, we discuss how such modules are formed and the experimental and theoretical approaches that can be used to investigate them, using examples from polynucleotide-protein interactions, vesicle transport and signal transduction to illustrate the underlying principles. Further progress in this field, where systems biology and biochemistry meet, will depend on iterative validation of the experimental and theoretical approaches.
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Affiliation(s)
- Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik, Charité Universitätsmedizin Berlin, Campus Mitte, Charitéplatz 1, 10098 Berlin, Germany.
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130
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Grosshans BL, Ortiz D, Novick P. Rabs and their effectors: achieving specificity in membrane traffic. Proc Natl Acad Sci U S A 2006; 103:11821-7. [PMID: 16882731 PMCID: PMC1567661 DOI: 10.1073/pnas.0601617103] [Citation(s) in RCA: 780] [Impact Index Per Article: 43.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Rab proteins constitute the largest branch of the Ras GTPase superfamily. Rabs use the guanine nucleotide-dependent switch mechanism common to the superfamily to regulate each of the four major steps in membrane traffic: vesicle budding, vesicle delivery, vesicle tethering, and fusion of the vesicle membrane with that of the target compartment. These different tasks are carried out by a diverse collection of effector molecules that bind to specific Rabs in their GTP-bound state. Recent advances have not only greatly extended the number of known Rab effectors, but have also begun to define the mechanisms underlying their distinct functions. By binding to the guanine nucleotide exchange proteins that activate the Rabs certain effectors act to establish positive feedback loops that help to define and maintain tightly localized domains of activated Rab proteins, which then serve to recruit other effector molecules. Additionally, Rab cascades and Rab conversions appear to confer directionality to membrane traffic and couple each stage of traffic with the next along the pathway.
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Affiliation(s)
- Bianka L. Grosshans
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520
| | - Darinel Ortiz
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520
| | - Peter Novick
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520
- To whom correspondence should be addressed. E-mail:
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131
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Affiliation(s)
- Joaquín Arribas
- Medical Oncology Research Program, Vall d'Hebron University Hospital Research Institute, 08035, Barcelona, Spain.
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Vasile E, Oka T, Ericsson M, Nakamura N, Krieger M. IntraGolgi distribution of the Conserved Oligomeric Golgi (COG) complex. Exp Cell Res 2006; 312:3132-41. [PMID: 16857184 DOI: 10.1016/j.yexcr.2006.06.005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Revised: 06/12/2006] [Accepted: 06/12/2006] [Indexed: 11/30/2022]
Abstract
The Conserved Oligomeric Golgi (COG) complex is an eight-subunit (Cog1-8) peripheral Golgi protein involved in membrane trafficking and glycoconjugate synthesis. COG appears to participate in retrograde vesicular transport and is required to maintain normal Golgi structure and function. COG mutations interfere with normal transport, distribution, and/or stability of Golgi proteins associated with glycoconjugate synthesis and trafficking, and lead to failure of spermatogenesis in Drosophila melanogaster, misdirected migration of gonadal distal tip cells in Caenorhabditis elegans, and type II congenital disorders of glycosylation in humans. The mechanism by which COG influences Golgi structure and function is unclear. Immunogold electron microscopy was used to visualize the intraGolgi distribution of a functional, hemagglutinin epitope-labeled COG subunit, Cog1-HA, that complements the Cog1-deficiency in Cog1-null Chinese hamster ovary cells. COG was found to be localized primarily on or in close proximity to the tips and rims of the Golgi's cisternae and their associated vesicles and on vesicles and vesiculo-tubular structures seen on both the cis and trans-Golgi Network faces of the cisternal stacks, in some cases on COPI containing vesicles. These findings support the proposal that COG is directly involved in controlling vesicular retrograde transport of Golgi resident proteins throughout the Golgi apparatus.
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Affiliation(s)
- Eliza Vasile
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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133
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Steet R, Kornfeld S. COG-7-deficient Human Fibroblasts Exhibit Altered Recycling of Golgi Proteins. Mol Biol Cell 2006; 17:2312-21. [PMID: 16510524 PMCID: PMC1446086 DOI: 10.1091/mbc.e05-08-0822] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Recently, we reported that two siblings presenting with the clinical syndrome congenital disorders of glycosylation (CDG) have mutations in the gene encoding Cog7p, a member of the conserved oligomeric Golgi (COG) complex. In this study, we analyzed the localization and trafficking of multiple Golgi proteins in patient fibroblasts under a variety of conditions. Although the immunofluorescent staining pattern of several Golgi proteins was indistinguishable from normal, the staining of endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC)-53 and the vesicular-soluble N-ethylmaleimide-sensitive factor attachment protein receptors GS15 and GS28 was abnormal, and the steady-state level of GS15 was greatly decreased. Retrograde transport of multiple Golgi proteins to the ER in patient fibroblasts via brefeldin A-induced tubules was significantly slower than occurs in normal fibroblasts, whereas anterograde protein trafficking was much less affected. After prolonged treatment with brefeldin A, several Golgi proteins were detected in clusters that colocalize with the microtubule-organizing center in patient cells. All of these abnormalities were normalized in COG7-corrected patient fibroblasts. These results serve to better define the role of the COG complex in facilitating protein trafficking between the Golgi and ER and provide a diagnostic framework for the identification of CDG defects involving trafficking proteins.
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Affiliation(s)
- Richard Steet
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
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