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Adhikari P, Ayo TE, Vines JC, Sugita S, Xu H. Exocytic machineries differentially control mediator release from allergen-triggered RBL-2H3 cells. Inflamm Res 2023; 72:639-649. [PMID: 36725743 DOI: 10.1007/s00011-023-01698-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2022] [Revised: 01/06/2023] [Accepted: 01/23/2023] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND Mast cells utilize SNAREs (soluble-N-ethyl-maleimide sensitive factor attachment protein receptors) and SM (Sec1/Munc18) proteins to secrete/exocytose a variety of proinflammatory mediators. However, whether a common SNARE-SM machinery is responsible remains unclear. METHODS Four vesicle/granule-anchored SNAREs (VAMP2, VAMP3, VAMP7, and VAMP8) and two Munc18 homologs (Munc18a and Munc18b) were systematically knocked down or knocked out in RBL-2H3 mast cells and antigen-induced release of β-hexosaminidase, histamine, serotonin, and TNF was examined. Phenotypes were validated by rescue experiments. Immunofluorescence studies were performed to determine the subcellular distribution of key players. RESULTS The reduction of VAMP8 expression inhibited the exocytosis of β-hexosaminidase, histamine, and serotonin but not TNF. Unexpectedly, however, confocal microscopy revealed substantial co-localization between VAMP8 and TNF, and between TNF and serotonin. Meanwhile, the depletion of other VAMPs, including knockout of VAMP3, had no impact on the release of any of the mediators examined. On the other hand, TNF exocytosis was diminished specifically in stable Munc18bknockdown cells, in a fashion that was rescued by exogenous, RNAi-resistant Munc18b. In line with this, TNF was co-localized with Munc18b (47%) to a much greater extent than with Munc18a (13%). CONCLUSION Distinct exocytic pathways exist in mast cells for the release of different mediators.
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Affiliation(s)
- Pratikshya Adhikari
- Center for Molecular and Cellular Biosciences, School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, Hattiesburg, MS, 39406, USA
| | - Tolulope E Ayo
- Center for Molecular and Cellular Biosciences, School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, Hattiesburg, MS, 39406, USA
| | - John C Vines
- Center for Molecular and Cellular Biosciences, School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, Hattiesburg, MS, 39406, USA
| | - Shuzo Sugita
- Division of Fundamental Neurobiology, University Health Network, Toronto, ON, M5T 2S8, Canada
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Hao Xu
- Center for Molecular and Cellular Biosciences, School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, Hattiesburg, MS, 39406, USA.
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2
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Liu F, He R, Zhu M, Zhou L, Liu Y, Yu H. Assembly-promoting protein Munc18c stimulates SNARE-dependent membrane fusion through its SNARE-like peptide. J Biol Chem 2022; 298:102470. [PMID: 36087838 PMCID: PMC9547204 DOI: 10.1016/j.jbc.2022.102470] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Revised: 09/02/2022] [Accepted: 09/03/2022] [Indexed: 11/19/2022] Open
Abstract
Intracellular vesicle fusion requires the soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and their cognate Sec1/Munc18 (SM) proteins. How SM proteins act in concert with trans-SNARE complexes to promote membrane fusion remains incompletely understood. Munc18c, a broadly distributed SM protein, selectively regulates multiple exocytotic pathways, including GLUT4 exocytosis. Here, using an in vitro reconstituted system, we discovered a SNARE-like peptide (SLP), conserved in Munc18-1 of synaptic exocytosis, is crucial to the stimulatory activity of Munc18c in vesicle fusion. The direct stimulation of the SNARE-mediated fusion reaction by SLP further supported the essential role of this fragment. Interestingly, we found SLP strongly accelerates the membrane fusion rate when anchored to the target membrane but not the vesicle membrane, suggesting it primarily interacts with t-SNAREs in cis to drive fusion. Furthermore, we determined the SLP fragment is competitive with the full-length Munc18c protein and specific to the cognate v-SNARE isoforms, supporting how it could resemble Munc18c’s activity in membrane fusion. Together, our findings demonstrate that Munc18c facilitates SNARE-dependent membrane fusion through SLP, revealing that the t-SNARE-SLP binding mode might be a conserved mechanism for the stimulatory function of SM proteins in vesicle fusion.
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Affiliation(s)
- Furong Liu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Ruyue He
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Min Zhu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China
| | - Lin Zhou
- School of Chemistry and Bioengineering, Nanjing Normal University Taizhou College, Taizhou, China
| | - Yinghui Liu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China.
| | - Haijia Yu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China.
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3
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Yu H, Crisman L, Stowell MHB, Shen J. Functional Reconstitution of Intracellular Vesicle Fusion Using Purified SNAREs and Sec1/Munc18 (SM) Proteins. Methods Mol Biol 2019; 1860:237-249. [PMID: 30317509 DOI: 10.1007/978-1-4939-8760-3_15] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The fusion of intracellular vesicles with target membranes is mediated by two classes of conserved molecules-soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAP receptors or SNAREs) and Sec1/Munc18 (SM) proteins. A conserved function of SM proteins is to recognize their cognate trans-SNARE complexes and accelerate fusion kinetics. Here, we describe a physiologically relevant reconstitution system in which macromolecular crowding agents are included to recapitulate the crowded intracellular environment. Through this system, we elucidate the molecular mechanisms by which SNAREs and SM proteins drive vesicle fusion.
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Affiliation(s)
- Haijia Yu
- Jiangsu Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China. .,Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA.
| | - Lauren Crisman
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA
| | - Michael H B Stowell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA
| | - Jingshi Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA.
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4
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RABIF/MSS4 is a Rab-stabilizing holdase chaperone required for GLUT4 exocytosis. Proc Natl Acad Sci U S A 2017; 114:E8224-E8233. [PMID: 28894007 DOI: 10.1073/pnas.1712176114] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Rab GTPases are switched from their GDP-bound inactive conformation to a GTP-bound active state by guanine nucleotide exchange factors (GEFs). The first putative GEFs isolated for Rabs are RABIF (Rab-interacting factor)/MSS4 (mammalian suppressor of Sec4) and its yeast homolog DSS4 (dominant suppressor of Sec4). However, the biological function and molecular mechanism of these molecules remained unclear. In a genome-wide CRISPR genetic screen, we isolated RABIF as a positive regulator of exocytosis. Knockout of RABIF severely impaired insulin-stimulated GLUT4 exocytosis in adipocytes. Unexpectedly, we discovered that RABIF does not function as a GEF, as previously assumed. Instead, RABIF promotes the stability of Rab10, a key Rab in GLUT4 exocytosis. In the absence of RABIF, Rab10 can be efficiently synthesized but is rapidly degraded by the proteasome, leading to exocytosis defects. Strikingly, restoration of Rab10 expression rescues exocytosis defects, bypassing the requirement for RABIF. These findings reveal a crucial role of RABIF in vesicle transport and establish RABIF as a Rab-stabilizing holdase chaperone, a previously unrecognized mode of Rab regulation independent of its GDP-releasing activity. Besides Rab10, RABIF also regulates the stability of two other Rab GTPases, Rab8 and Rab13, suggesting that the requirement of holdase chaperones is likely a general feature of Rab GTPases.
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5
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Dummer PD, Limou S, Rosenberg AZ, Heymann J, Nelson G, Winkler CA, Kopp JB. APOL1 Kidney Disease Risk Variants: An Evolving Landscape. Semin Nephrol 2016. [PMID: 26215860 DOI: 10.1016/j.semnephrol.2015.04.008] [Citation(s) in RCA: 107] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Apolipoprotein L1 (APOL1) genetic variants account for much of the excess risk of chronic and end-stage kidney disease, which results in a significant global health disparity for persons of African ancestry. We estimate the lifetime risk of kidney disease in APOL1 dual-risk allele individuals to be at least 15%. Experimental evidence suggests a direct role of APOL1 in pore formation, cellular injury, and programmed cell death in renal injury. The APOL1 BH3 motif, often associated with cell death, is unlikely to play a role in APOL1-induced cytotoxicity because it is not conserved within the APOL family and is dispensable for cell death in vitro. We discuss two models for APOL1 trypanolytic activity: one involving lysosome permeabilization and another involving colloid-osmotic swelling of the cell body, as well as their relevance to human pathophysiology. Experimental evidence from human cell culture models suggests that both mechanisms may be operative. A systems biology approach whereby APOL1-associated perturbations in gene and protein expression in affected individuals are correlated with molecular pathways may be productive to elucidate APOL1 function in vivo.
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Affiliation(s)
- Patrick D Dummer
- Kidney Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - Sophie Limou
- Molecular Epidemiology Genetics Section, Center for Cancer Research, National Cancer Institute, Frederick MD
| | - Avi Z Rosenberg
- Kidney Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD; Department of Pathology Johns Hopkins University, Baltimore, MD
| | - Jurgen Heymann
- Kidney Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - George Nelson
- Molecular Epidemiology Genetics Section, Center for Cancer Research, National Cancer Institute, Frederick MD
| | - Cheryl A Winkler
- Molecular Epidemiology Genetics Section, Center for Cancer Research, National Cancer Institute, Frederick MD
| | - Jeffrey B Kopp
- Kidney Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD.
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Shen C, Rathore SS, Yu H, Gulbranson DR, Hua R, Zhang C, Schoppa NE, Shen J. The trans-SNARE-regulating function of Munc18-1 is essential to synaptic exocytosis. Nat Commun 2015; 6:8852. [PMID: 26572858 PMCID: PMC4668942 DOI: 10.1038/ncomms9852] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Accepted: 10/09/2015] [Indexed: 11/09/2022] Open
Abstract
The fusion of neurotransmitter-filled synaptic vesicles with the plasma membrane requires two classes of molecules-SNAP receptor (SNARE) and Sec1/Munc18 (SM) protein. Reconstitution studies suggest that the SM protein Munc18-1 promotes the zippering of trans-SNARE complexes and accelerates the kinetics of SNARE-dependent membrane fusion. However, the physiological role of this trans-SNARE-regulating function in synaptic exocytosis remains to be established. Here we first demonstrate that two mutations in the vesicle-anchored v-SNARE selectively impair the ability of Munc18-1 to promote trans-SNARE zippering, whereas other known Munc18-1/SNARE-binding modes are unaffected. In cultured neurons, these v-SNARE mutations strongly inhibit spontaneous as well as evoked neurotransmitter release, providing genetic evidence for the trans-SNARE-regulating function of Munc18-1 in synaptic exocytosis. Finally, we show that the trans-SNARE-regulating function of Munc18-1 is compromised by a mutation associated with Ohtahara Syndrome, a severe form of epilepsy.
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Affiliation(s)
- Chong Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Shailendra S Rathore
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Haijia Yu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Daniel R Gulbranson
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Rui Hua
- State Key Laboratory of Membrane Biology, School of Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
| | - Chen Zhang
- State Key Laboratory of Membrane Biology, School of Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
| | - Nathan E Schoppa
- Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado 80045, USA
| | - Jingshi Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, Colorado 80309, USA
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7
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Yu H, Rathore SS, Shen C, Liu Y, Ouyang Y, Stowell MH, Shen J. Reconstituting Intracellular Vesicle Fusion Reactions: The Essential Role of Macromolecular Crowding. J Am Chem Soc 2015; 137:12873-83. [PMID: 26431309 DOI: 10.1021/jacs.5b08306] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intracellular vesicle fusion is mediated by SNAREs and Sec1/Munc18 (SM) proteins. Despite intensive efforts, the SNARE-SM mediated vesicle fusion reaction has not been faithfully reconstituted in biochemical assays. Here, we present an unexpected discovery that macromolecular crowding is required for reconstituting the vesicle fusion reaction in vitro. Macromolecular crowding is known to profoundly influence the kinetic and thermodynamic behaviors of macromolecules, but its role in membrane transport processes such as vesicle fusion remains unexplored. We introduced macromolecular crowding agents into reconstituted fusion reactions to mimic the crowded cellular environment. In this crowded assay, SNAREs and SM proteins acted in concert to drive efficient membrane fusion. In uncrowded assays, by contrast, SM proteins failed to associate with the SNAREs and the fusion rate decreased more than 30-fold, close to undetectable levels. The activities of SM proteins were strictly specific to their cognate SNARE isoforms and sensitive to biologically relevant mutations, further supporting that the crowded fusion assay accurately recapitulates the vesicle fusion reaction. Using this crowded fusion assay, we also showed that the SNARE-SM mediated fusion reaction can be modulated by two additional factors: NSF and α-SNAP. These findings suggest that the vesicle fusion machinery likely has been evolutionarily selected to function optimally in the crowded milieu of the cell. Accordingly, macromolecular crowding should constitute an integral element of any reconstituted fusion assay.
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Affiliation(s)
- Haijia Yu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Shailendra S Rathore
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Chong Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Yinghui Liu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Yan Ouyang
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Michael H Stowell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Jingshi Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
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8
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Yu H, Rathore SS, Gulbranson DR, Shen J. The N- and C-terminal domains of tomosyn play distinct roles in soluble N-ethylmaleimide-sensitive factor attachment protein receptor binding and fusion regulation. J Biol Chem 2014; 289:25571-80. [PMID: 25063806 DOI: 10.1074/jbc.m114.591487] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tomosyn negatively regulates SNARE-dependent exocytic pathways including insulin secretion, GLUT4 exocytosis, and neurotransmitter release. The molecular mechanism of tomosyn, however, has not been fully elucidated. Here, we reconstituted SNARE-dependent fusion reactions in vitro to recapitulate the tomosyn-regulated exocytic pathways. We then expressed and purified active full-length tomosyn and examined how it regulates the reconstituted SNARE-dependent fusion reactions. Using these defined fusion assays, we demonstrated that tomosyn negatively regulates SNARE-mediated membrane fusion by inhibiting the assembly of the ternary SNARE complex. Tomosyn recognizes the t-SNARE complex and prevents its pairing with the v-SNARE, therefore arresting the fusion reaction at a pre-docking stage. The inhibitory function of tomosyn is mediated by its C-terminal domain (CTD) that contains an R-SNARE-like motif, confirming previous studies carried out using truncated tomosyn fragments. Interestingly, the N-terminal domain (NTD) of tomosyn is critical (but not sufficient) to the binding of tomosyn to the syntaxin monomer, indicating that full-length tomosyn possesses unique features not found in the widely studied CTD fragment. Finally, we showed that the inhibitory function of tomosyn is dominant over the stimulatory activity of the Sec1/Munc18 protein in fusion. We suggest that tomosyn uses its CTD to arrest SNARE-dependent fusion reactions, whereas its NTD is required for the recruitment of tomosyn to vesicle fusion sites through syntaxin interaction.
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Affiliation(s)
- Haijia Yu
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Shailendra S Rathore
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Daniel R Gulbranson
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Jingshi Shen
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
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9
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Comparative studies of Munc18c and Munc18-1 reveal conserved and divergent mechanisms of Sec1/Munc18 proteins. Proc Natl Acad Sci U S A 2013; 110:E3271-80. [PMID: 23918365 DOI: 10.1073/pnas.1311232110] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Sec1/Munc18 (SM) family proteins are essential for every vesicle fusion pathway. The best-characterized SM protein is the synaptic factor Munc18-1, but it remains unclear whether its functions represent conserved mechanisms of SM proteins or specialized activities in neurotransmitter release. To address this question, we dissected Munc18c, a functionally distinct SM protein involved in nonsynaptic exocytic pathways. We discovered that Munc18c binds to the trans-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex and strongly accelerates the fusion rate. Further analysis suggests that Munc18c recognizes both vesicle-rooted SNARE and target membrane-associated SNAREs, and promotes trans-SNARE zippering at the postdocking stage of the fusion reaction. The stimulation of fusion by Munc18c is specific to its cognate SNARE isoforms. Because Munc18-1 regulates fusion in a similar manner, we conclude that one conserved function of SM proteins is to bind their cognate trans-SNARE complexes and accelerate fusion kinetics. Munc18c also binds syntaxin-4 monomer but does not block target membrane-associated SNARE assembly, in agreement with our observation that six- to eightfold increases in Munc18c expression do not inhibit insulin-stimulated glucose uptake in adipocytes. Thus, the inhibitory "closed" syntaxin binding mode demonstrated for Munc18-1 is not conserved in Munc18c. Unexpectedly, we found that Munc18c recognizes the N-terminal region of the vesicle-rooted SNARE, whereas Munc18-1 requires the C-terminal sequences, suggesting that the architecture of the SNARE/SM complex likely differs across fusion pathways. Together, these comparative studies of two distinct SM proteins reveal conserved as well as divergent mechanisms of SM family proteins in intracellular vesicle fusion.
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Yu H, Rathore SS, Shen J. Synip arrests soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent membrane fusion as a selective target membrane SNARE-binding inhibitor. J Biol Chem 2013; 288:18885-93. [PMID: 23665562 DOI: 10.1074/jbc.m113.465450] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The vesicle fusion reaction in regulated exocytosis requires the concerted action of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) core fusion engine and a group of SNARE-binding regulatory factors. The regulatory mechanisms of vesicle fusion remain poorly understood in most exocytic pathways. Here, we reconstituted the SNARE-dependent vesicle fusion reaction of GLUT4 exocytosis in vitro using purified components. Using this defined fusion system, we discovered that the regulatory factor synip binds to GLUT4 exocytic SNAREs and inhibits the docking, lipid mixing, and content mixing of the fusion reaction. Synip arrests fusion by binding the target membrane SNARE (t-SNARE) complex and preventing the initiation of ternary SNARE complex assembly. Although synip also interacts with the syntaxin-4 monomer, it does not inhibit the pairing of syntaxin-4 with SNAP-23. Interestingly, synip selectively arrests the fusion reactions reconstituted with its cognate SNAREs, suggesting that the defined system recapitulates the biological functions of the vesicle fusion proteins. We further showed that the inhibitory function of synip is dominant over the stimulatory activity of Sec1/Munc18 proteins. Importantly, the inhibitory function of synip is distinct from how other fusion inhibitors arrest SNARE-dependent membrane fusion and therefore likely represents a novel regulatory mechanism of vesicle fusion.
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Affiliation(s)
- Haijia Yu
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309, USA
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