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Shvarev D, König C, Susan N, Langemeyer L, Walter S, Perz A, Fröhlich F, Ungermann C, Moeller A. Structure of the endosomal CORVET tethering complex. Nat Commun 2024; 15:5227. [PMID: 38898033 PMCID: PMC11187117 DOI: 10.1038/s41467-024-49137-9] [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: 11/09/2023] [Accepted: 05/24/2024] [Indexed: 06/21/2024] Open
Abstract
Cells depend on their endolysosomal system for nutrient uptake and downregulation of plasma membrane proteins. These processes rely on endosomal maturation, which requires multiple membrane fusion steps. Early endosome fusion is promoted by the Rab5 GTPase and its effector, the hexameric CORVET tethering complex, which is homologous to the lysosomal HOPS. How these related complexes recognize their specific target membranes remains entirely elusive. Here, we solve the structure of CORVET by cryo-electron microscopy and revealed its minimal requirements for membrane tethering. As expected, the core of CORVET and HOPS resembles each other. However, the function-defining subunits show marked structural differences. Notably, we discover that unlike HOPS, CORVET depends not only on Rab5 but also on phosphatidylinositol-3-phosphate (PI3P) and membrane lipid packing defects for tethering, implying that an organelle-specific membrane code enables fusion. Our data suggest that both shape and membrane interactions of CORVET and HOPS are conserved in metazoans, thus providing a paradigm how tethering complexes function.
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Affiliation(s)
- Dmitry Shvarev
- Department of Biology/Chemistry, Structural Biology Section, Osnabrück University, 49076, Osnabrück, Germany
| | - Caroline König
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, 49076, Osnabrück, Germany
| | - Nicole Susan
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, 49076, Osnabrück, Germany
| | - Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, 49076, Osnabrück, Germany
- Center of Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, 49076, Osnabrück, Germany
| | - Stefan Walter
- Center of Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, 49076, Osnabrück, Germany
| | - Angela Perz
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, 49076, Osnabrück, Germany
| | - Florian Fröhlich
- Center of Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, 49076, Osnabrück, Germany
- Department of Biology/Chemistry, Bioanalytical Chemistry Section, Osnabrück University, 49076, Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, 49076, Osnabrück, Germany.
- Center of Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, 49076, Osnabrück, Germany.
| | - Arne Moeller
- Department of Biology/Chemistry, Structural Biology Section, Osnabrück University, 49076, Osnabrück, Germany.
- Center of Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, 49076, Osnabrück, Germany.
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2
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Orr A, Wickner W. Sec18 binds the tethering/SM complex HOPS to engage the Qc-SNARE for membrane fusion. Mol Biol Cell 2024; 35:ar71. [PMID: 38536444 PMCID: PMC11151092 DOI: 10.1091/mbc.e24-02-0060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2024] [Revised: 03/18/2024] [Accepted: 03/22/2024] [Indexed: 04/18/2024] Open
Abstract
Membrane fusion is regulated by Rab GTPases, their tethering effectors such as HOPS, SNARE proteins on each fusion partner, SM proteins to catalyze SNARE assembly, Sec17 (SNAP), and Sec18 (NSF). Though concentrated HOPS can support fusion without Sec18, we now report that fusion falls off sharply at lower HOPS levels, where direct Sec18 binding to HOPS restores fusion. This Sec18-dependent fusion needs adenine nucleotide but neither ATP hydrolysis nor Sec17. Sec18 enhances HOPS recognition of the Qc-SNARE. With high levels of HOPS, Qc has a Km for fusion of a few nM. Either lower HOPS levels, or substitution of a synthetic tether for HOPS, strikingly increases the Km for Qc to several hundred nM. With dilute HOPS, Sec18 returns the Km for Qc to low nM. In contrast, HOPS concentration and Sec18 have no effect on Qb-SNARE recognition. Just as Qc is required for fusion but not for the initial assembly of SNAREs in trans, impaired Qc recognition by limiting HOPS without Sec18 still allows substantial trans-SNARE assembly. Thus, in addition to the known Sec18 functions of disassembling SNARE complexes, oligomerizing Sec17 for membrane association, and allowing Sec17 to drive fusion without complete SNARE zippering, we report a fourth Sec18 function, the Sec17-independent binding of Sec18 to HOPS to enhance functional Qc-SNARE engagement.
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Affiliation(s)
- Amy Orr
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
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3
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Koike S, Jahn R. Rab GTPases and phosphoinositides fine-tune SNAREs dependent targeting specificity of intracellular vesicle traffic. Nat Commun 2024; 15:2508. [PMID: 38509070 PMCID: PMC10954720 DOI: 10.1038/s41467-024-46678-x] [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: 02/06/2023] [Accepted: 03/05/2024] [Indexed: 03/22/2024] Open
Abstract
In the secretory pathway the destination of trafficking vesicles is determined by specific proteins that, with the notable exception of SNAREs, are recruited from soluble pools. Previously we have shown that microinjected proteoliposomes containing early or late endosomal SNAREs, respectively, are targeted to the corresponding endogenous compartments, with targeting specificity being dependent on the recruitment of tethering factors by some of the SNAREs. Here, we show that targeting of SNARE-containing liposomes is refined upon inclusion of polyphosphoinositides and Rab5. Intriguingly, targeting specificity is dependent on the concentration of PtdIns(3)P, and on the recruitment of PtdIns(3)P binding proteins such as rabenosyn-5 and PIKfyve, with conversion of PtdIns(3)P into PtdIns(3,5)P2 re-routing the liposomes towards late endosomes despite the presence of GTP-Rab5 and early endosomal SNAREs. Our data reveal a complex interplay between permissive and inhibitory targeting signals that sharpen a basic targeting and fusion machinery for conveying selectivity in intracellular membrane traffic.
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Affiliation(s)
- Seiichi Koike
- Laboratory of Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- University of Toyama, Laboratory of Molecular and Cellular Biology, Department of Life Sciences and Bioengineering, 3190 Gofuku, Toyama City, 930-8555, Japan
| | - Reinhard Jahn
- Laboratory of Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
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4
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Andhare D, Ragusa MJ. A new GUV-based assay to reconstitute membrane tethering in vitro demonstrates the vesicle tethering ability of the selective autophagy scaffold Atg11. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.19.572332. [PMID: 38187578 PMCID: PMC10769207 DOI: 10.1101/2023.12.19.572332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
Membrane tethering is essential for the generation of organelle contact sites and to anchor incoming vesicles to their target membranes before vesicle fusion. During autophagy in yeast, tethering of 30 nm vesicles to cargo is one of the first steps in the generation of the isolation membrane that engulfs the cargo to be degraded. While membrane tethering is critical for cellular function, many of the current biochemical techniques to assay for membrane tethering rely on indirect readouts and are limited in their ability to monitor protein localization at sites of tethering. As such, we developed a fluorescence-microscopy-based GUV liposome tethering assay (GLT) to directly visualize membrane tethering and monitor protein localization at tethering sites simultaneously. We initially used GLT with engineered membrane tethers to demonstrate the ease of use, versatility and sensitivity of the assay. We also demonstrated that the selective autophagy scaffolding protein Atg11 can bind, and tether negatively charged membranes but is unable to bind GUVs mimicking the charge of the outer mitochondrial membrane. Atg11 instead requires the selective autophagy receptor Atg32 to be recruited to mitochondrial membranes. Lastly, we demonstrate that Atg11 bound to Atg32 on GUVs can tether negatively charged vesicles to GUVs. Collectively, our results reconstitute one of the first steps during the initiation of mitochondrial autophagy and highlight the versatility of GLT to study a range of membrane tethering events biochemically.
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Affiliation(s)
- Devika Andhare
- Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA
| | - Michael J Ragusa
- Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA
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5
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Pyne S, Pyne P, Mitra RK. The explicit role of interfacial hydration during polyethylene glycol induced lipid fusion: a THz spectroscopic investigation. Phys Chem Chem Phys 2023; 25:31326-31334. [PMID: 37960951 DOI: 10.1039/d3cp04868c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
While the phenomenon of excipient mediated membrane fusion has been studied widely, the inherent role of interfacial hydration involved in the process has mostly remained unaddressed. Here we report the experimental validation of the fact that PEG-induced membrane fusion is associated with the dehydration of the membrane(s). We explore the explicit hydration behavior at three different lipids (DOPC, POPC and DPPC) membranes with different aliphatic tails as they undergo fusogenic transition in the presence of PEG of average molecular weight of 4000 using THz-FTIR spectroscopy in the frequency window of 1.5-13.5 THz. Dynamic light scattering and electron microscopic measurements confirm the formation of different intermediate steps of the liposomes during the fusion process: bilayer aggregation, destabilization and finally lipid fusion. We observe that membrane hydration follows a systematic trend with the lipid specificity as the fusion process sets in.
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Affiliation(s)
- Sumana Pyne
- Department of Chemical and Biological Sciences, S N Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
| | - Partha Pyne
- Department of Chemical and Biological Sciences, S N Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
| | - Rajib Kumar Mitra
- Department of Chemical and Biological Sciences, S N Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
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6
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Orr A, Wickner W. PI3P regulates multiple stages of membrane fusion. Mol Biol Cell 2023; 34:ar17. [PMID: 36735517 PMCID: PMC10011722 DOI: 10.1091/mbc.e22-10-0486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The conserved catalysts of intracellular membrane fusion are Rab-family GTPases, effector complexes that bind Rabs for membrane tethering, SNARE proteins of the R, Qa, Qb, and Qc families, and SNARE chaperones of the SM, Sec17/SNAP, and Sec18/NSF families. Yeast vacuole fusion is regulated by phosphatidylinositol-3-phosphate (PI3P). PI3P binds directly to the vacuolar Qc-SNARE and to HOPS, the vacuolar tethering/SM complex. We now report several distinct functions of PI3P in fusion. PI3P binds the N-terminal PX domain of the Qc-SNARE to enhance its engagement for fusion. Even when Qc has been preassembled with the Qa- and Qb-SNAREs, PI3P still promotes trans-SNARE assembly and fusion between these 3Q proteoliposomes and those with R-SNARE, whether with the natural HOPS tether or with a synthetic tether. With HOPS, efficient trans-SNARE complex formation needs PI3P on the 3Q-SNARE proteoliposomes, in cis to the Qc. PI3P is also needed for HOPS to confer resistance to Sec17/Sec18. With a synthetic tether, fusion is supported by PI3P on either fusion partner membrane, but this fusion is blocked by Sec17/Sec18. PI3P thus supports multiple stages of fusion: the engagement of the Qc-SNARE, trans-SNARE complex formation with preassembled Q-SNAREs, HOPS protection of SNARE complexes from Sec17/Sec18, and fusion per se after tethering and Q-SNARE assembly.
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Affiliation(s)
- Amy Orr
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
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7
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Orr A, Wickner W. Sec18 supports membrane fusion by promoting Sec17 membrane association. Mol Biol Cell 2022; 33:ar127. [PMID: 36103252 PMCID: PMC9634978 DOI: 10.1091/mbc.e22-07-0274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Membrane fusion is driven by Sec17, Sec18, and SNARE zippering. Sec17 bound to SNAREs promotes fusion through its membrane-proximal N-terminal apolar loop domain. At its membrane-distal end, Sec17 serves as a high-affinity receptor for Sec18. At that distance from the fusion site, it has been unclear how Sec18 can aid Sec17 to promote fusion. We now report that Sec18, with ATPγS, lowers the Km of Sec17 for fusion. A C-terminal and membrane-distal Sec17 mutation, L291A,L292A, diminishes Sec17 affinity for Sec18. High levels of wild-type Sec17 or Sec17-L291AL292A show equivalent fusion without Sec18, but Sec18 causes far less fusion enhancement with low levels of Sec17-L291AL292A than with wild-type Sec17. Another mutant, Sec17-F21SM22S, has reduced N-loop apolarity. Only very high levels of this mutant protein support fusion, but Sec18 still lowers the apparent fusion Km for Sec17-F21SM22S. Thus Sec18 stimulates fusion through Sec17 and acts at the well-described interface between Sec18 and Sec17. ATP acts as a ligand to activate Sec18 for Sec17-dependent fusion, but ATP hydrolysis is not required. Even without SNAREs, Sec18 and Sec17 exhibit interdependent stable association with lipids, with several Sec17 bound for each Sec18 hexamer, explaining how Sec18 stabilization of surface-concentrated clusters of Sec17 lowers the Sec17 Km for assembly with SNAREs. Each of the associations, between SNARE complex, Sec18, Sec17, and lipid, helps assemble the fusion machinery.
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Affiliation(s)
- Amy Orr
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, 7200 Vail Building, Hanover, NH 03755
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, 7200 Vail Building, Hanover, NH 03755,*Address correspondence to: William Wickner ()
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8
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Anderson J, Walker G, Pu J. BORC-ARL8-HOPS ensemble is required for lysosomal cholesterol egress through NPC2. Mol Biol Cell 2022; 33:ar81. [PMID: 35653304 PMCID: PMC9582633 DOI: 10.1091/mbc.e21-11-0595-t] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 05/16/2022] [Accepted: 05/24/2022] [Indexed: 11/11/2022] Open
Abstract
Lysosomes receive extracellular and intracellular cholesterol and redistribute it throughout the cell. Cholesterol egress from lysosomes is critical for cholesterol homeostasis, and its failure underlies the pathogenesis of genetic disorders such as Niemann-Pick C (NPC) disease. Here we report that the BLOC one-related complex (BORC)-ARL8-homotypic fusion and protein sorting (HOPS) ensemble is required for egress of free cholesterol from lysosomes and for storage of esterified cholesterol in lipid droplets. Depletion of BORC, ARL8, or HOPS does not alter the localization of the lysosomal transmembrane cholesterol transporter NPC1 to degradative compartments but decreases the association of the luminal transporter NPC2 and increases NPC2 secretion. BORC-ARL8-HOPS depletion also increases lysosomal degradation of cation-independent (CI)-mannose 6-phosphate (M6P) receptor (MPR), which normally sorts NPC2 to the endosomal-lysosomal system and then is recycled to the trans-Golgi network. These defects likely result from impaired HOPS-dependent fusion of endosomal-lysosomal organelles and an uncharacterized function of HOPS in CI-MPR recycling. Our study demonstrates that the BORC-ARL8-HOPS ensemble is required for cholesterol egress from lysosomes by enabling CI-MPR-dependent trafficking of NPC2 to the endosomal-lysosomal system.
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Affiliation(s)
- Jacob Anderson
- Department of Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, NM 87131
- Autophagy, Inflammation, and Metabolism Center of Biomedical Research Excellence, University of New Mexico, Albuquerque, NM 87131
| | - Gerard Walker
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892
| | - Jing Pu
- Department of Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, NM 87131
- Autophagy, Inflammation, and Metabolism Center of Biomedical Research Excellence, University of New Mexico, Albuquerque, NM 87131
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9
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Emerging Concepts in Defective Macrophage Phagocytosis in Cystic Fibrosis. Int J Mol Sci 2022; 23:ijms23147750. [PMID: 35887098 PMCID: PMC9319215 DOI: 10.3390/ijms23147750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 07/09/2022] [Accepted: 07/11/2022] [Indexed: 01/18/2023] Open
Abstract
Cystic fibrosis (CF) is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Chronic inflammation and decline in lung function are major reasons for morbidity in CF. Mutant CFTR expressed in phagocytic cells such as macrophages contributes to persistent infection, inflammation, and lung disease in CF. Macrophages play a central role in innate immunity by eliminating pathogenic microbes by a process called phagocytosis. Phagocytosis is required for tissue homeostasis, balancing inflammation, and crosstalk with the adaptive immune system for antigen presentation. This review focused on (1) current understandings of the signaling underlying phagocytic mechanisms; (2) existing evidence for phagocytic dysregulation in CF; and (3) the emerging role of CFTR modulators in influencing CF phagocytic function. Alterations in CF macrophages from receptor initiation to phagosome formation are linked to disease progression in CF. A deeper understanding of macrophages in the context of CFTR and phagocytosis proteins at each step of phagosome formation might contribute to the new therapeutic development of dysregulated innate immunity in CF. Therefore, the review also indicates future areas of research in the context of CFTR and macrophages.
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10
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Langemeyer L, Ungermann C. Vesicle transport: Exocyst follows PIP 2 to tether membranes. Curr Biol 2022; 32:R748-R750. [PMID: 35820387 DOI: 10.1016/j.cub.2022.05.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A new study uses reconstituted, functional octameric exocyst complex to provide new insights into the assembly of this tethering complex and reveal how the activity of the lipid kinase PIP5K1C stimulated by Arf6 on exocytic vesicles allows for exocyst-mediated tethering at the plasma membrane.
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Affiliation(s)
- Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry Section and Center for Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, Barbarastrasse 13, 49076 Osnabrück, Germany.
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section and Center for Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, Barbarastrasse 13, 49076 Osnabrück, Germany.
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11
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van der Beek J, de Heus C, Liv N, Klumperman J. Quantitative correlative microscopy reveals the ultrastructural distribution of endogenous endosomal proteins. J Cell Biol 2022; 221:212877. [PMID: 34817533 PMCID: PMC8624803 DOI: 10.1083/jcb.202106044] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 10/22/2021] [Accepted: 11/01/2021] [Indexed: 02/07/2023] Open
Abstract
The key endosomal regulators Rab5, EEA1, and APPL1 are frequently applied in fluorescence microscopy to mark early endosomes, whereas Rab7 is used as a marker for late endosomes and lysosomes. However, endogenous levels of these proteins localize poorly in immuno-EM, and systematic studies on their native ultrastructural distributions are lacking. To address this gap, we here present a quantitative, on-section correlative light and electron microscopy (CLEM) approach. Using the sensitivity of fluorescence microscopy, we label hundreds of organelles that are subsequently visualized by EM and classified by ultrastructure. We show that Rab5 predominantly marks small, endocytic vesicles and early endosomes. EEA1 colocalizes with Rab5 on early endosomes, but unexpectedly also labels Rab5-negative late endosomes, which are positive for PI(3)P but lack Rab7. APPL1 is restricted to small Rab5-positive, tubulo-vesicular profiles. Rab7 primarily labels late endosomes and lysosomes. These data increase our understanding of the structural-functional organization of the endosomal system and introduce quantitative CLEM as a sensitive alternative for immuno-EM.
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Affiliation(s)
- Jan van der Beek
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute of Biomembranes, Utrecht University, Utrecht, the Netherlands
| | - Cecilia de Heus
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute of Biomembranes, Utrecht University, Utrecht, the Netherlands
| | - Nalan Liv
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute of Biomembranes, Utrecht University, Utrecht, the Netherlands
| | - Judith Klumperman
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute of Biomembranes, Utrecht University, Utrecht, the Netherlands
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12
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Torng T, Wickner W. Phosphatidylinositol and phosphatidylinositol-3-phosphate activate HOPS to catalyze SNARE assembly, allowing small headgroup lipids to support the terminal steps of membrane fusion. Mol Biol Cell 2021; 32:ar19. [PMID: 34495682 PMCID: PMC8693972 DOI: 10.1091/mbc.e21-07-0373] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Intracellular membrane fusion requires Rab GTPases, tethers, SNAREs of the R, Qa, Qb, and Qc families, and SNARE chaperones of the Sec17 (SNAP), Sec18 (NSF), and SM (Sec1/Munc18) families. The vacuolar HOPS complex combines the functions of membrane tethering and SM catalysis of SNARE assembly. HOPS is activated for this catalysis by binding to the vacuolar lipids and Rab. Of the eight major vacuolar lipids, we now report that phosphatidylinositol and phosphatidylinositol-3-phosphate are required to activate HOPS for SNARE complex assembly. These lipids plus ergosterol also allow full trans-SNARE complex assembly, yet do not support fusion, which is reliant on either phosphatidylethanolamine (PE) or on phosphatidic acid (PA), phosphatidylserine (PS), and diacylglycerol (DAG). Fusion with a synthetic tether and without HOPS, or even without SNAREs, still relies on either PE or on PS, PA, and DAG. These lipids are thus required for the terminal bilayer rearrangement step of fusion, distinct from the lipid requirements for the earlier step of activating HOPS for trans-SNARE assembly.
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Affiliation(s)
- Thomas Torng
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
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13
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Wilson ZN, Buysse D, West M, Ahrens D, Odorizzi G. Vacuolar H+-ATPase dysfunction rescues intralumenal vesicle cargo sorting in yeast lacking PI(3,5)P2 or Doa4. J Cell Sci 2021; 134:jcs258459. [PMID: 34342352 PMCID: PMC8353521 DOI: 10.1242/jcs.258459] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 06/25/2021] [Indexed: 12/19/2022] Open
Abstract
Endosomes undergo a maturation process highlighted by a reduction in lumenal pH, a conversion of surface markers that prime endosome-lysosome fusion and the sequestration of ubiquitylated transmembrane protein cargos within intralumenal vesicles (ILVs). We investigated ILV cargo sorting in mutant strains of the budding yeast Saccharomyces cerevisiae that are deficient for either the lysosomal/vacuolar signaling lipid PI(3,5)P2 or the Doa4 ubiquitin hydrolase that deubiquitylates ILV cargos. Disruption of PI(3,5)P2 synthesis or Doa4 function causes a defect in sorting of a subset of ILV cargos. We show that these cargo-sorting defects are suppressed by mutations that disrupt Vph1, a subunit of vacuolar H+-ATPase (V-ATPase) complexes that acidify late endosomes and vacuoles. We further show that Vph1 dysfunction increases endosome abundance, and disrupts vacuolar localization of Ypt7 and Vps41, two crucial mediators of endosome-vacuole fusion. Because V-ATPase inhibition attenuates this fusion and rescues the ILV cargo-sorting defects in yeast that lack PI(3,5)P2 or Doa4 activity, our results suggest that the V-ATPase has a role in coordinating ILV cargo sorting with the membrane fusion machinery. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
| | | | | | | | - Greg Odorizzi
- Department of Molecular Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
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14
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Song H, Torng TL, Orr AS, Brunger AT, Wickner WT. Sec17/Sec18 can support membrane fusion without help from completion of SNARE zippering. eLife 2021; 10:67578. [PMID: 33944780 PMCID: PMC8143792 DOI: 10.7554/elife.67578] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Accepted: 04/30/2021] [Indexed: 11/20/2022] Open
Abstract
Membrane fusion requires R-, Qa-, Qb-, and Qc-family SNAREs that zipper into RQaQbQc coiled coils, driven by the sequestration of apolar amino acids. Zippering has been thought to provide all the force driving fusion. Sec17/αSNAP can form an oligomeric assembly with SNAREs with the Sec17 C-terminus bound to Sec18/NSF, the central region bound to SNAREs, and a crucial apolar loop near the N-terminus poised to insert into membranes. We now report that Sec17 and Sec18 can drive robust fusion without requiring zippering completion. Zippering-driven fusion is blocked by deleting the C-terminal quarter of any Q-SNARE domain or by replacing the apolar amino acids of the Qa-SNARE that face the center of the 4-SNARE coiled coils with polar residues. These blocks, singly or combined, are bypassed by Sec17 and Sec18, and SNARE-dependent fusion is restored without help from completing zippering.
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Affiliation(s)
- Hongki Song
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Thomas L Torng
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Amy S Orr
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Axel T Brunger
- Howard Hughes Medical Institute and Department of Molecular and Cellular Physiology Stanford University, Stanford, United States
| | - William T Wickner
- Department of Biochemistry and Cell Biology Geisel School of Medicine at Dartmouth, Hanover, United States
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15
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Füllbrunn N, Li Z, Jorde L, Richter CP, Kurre R, Langemeyer L, Yu C, Meyer C, Enderlein J, Ungermann C, Piehler J, You C. Nanoscopic anatomy of dynamic multi-protein complexes at membranes resolved by graphene-induced energy transfer. eLife 2021; 10:62501. [PMID: 33513092 PMCID: PMC7847308 DOI: 10.7554/elife.62501] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Accepted: 12/28/2020] [Indexed: 11/30/2022] Open
Abstract
Insights into the conformational organization and dynamics of proteins complexes at membranes is essential for our mechanistic understanding of numerous key biological processes. Here, we introduce graphene-induced energy transfer (GIET) to probe axial orientation of arrested macromolecules at lipid monolayers. Based on a calibrated distance-dependent efficiency within a dynamic range of 25 nm, we analyzed the conformational organization of proteins and complexes involved in tethering and fusion at the lysosome-like yeast vacuole. We observed that the membrane-anchored Rab7-like GTPase Ypt7 shows conformational reorganization upon interactions with effector proteins. Ensemble and time-resolved single-molecule GIET experiments revealed that the HOPS tethering complex, when recruited via Ypt7 to membranes, is dynamically alternating between a ‘closed’ and an ‘open’ conformation, with the latter possibly interacting with incoming vesicles. Our work highlights GIET as a unique spectroscopic ruler to reveal the axial orientation and dynamics of macromolecular complexes at biological membranes with sub-nanometer resolution. Proteins are part of the building blocks of life and are essential for structure, function and regulation of every cell, tissue and organ of the body. Proteins adopt different conformations to work efficiently within the various environments of a cell. They can also switch between shapes. One way to monitor how proteins change their shapes involves energy transfer. This approach can measure how close two proteins, or two parts of the same protein, are, by using dye labels that respond to each other when they are close together. For example, in a method called FRET, one dye label absorbs light and transfers the energy to the other label, which emits it as a different color of light. However, FRET only works over short distances (less than 10nm apart or 1/100,000th of a millimeter), so it is not useful for larger proteins. Here, Füllbrunn, Li et al. developed a method called GIET that uses graphene to analyze the dynamic structures of proteins on membrane surfaces. Graphene is a type of carbon nanomaterial that can absorb energy from dye labels and could provide a way to study protein interactions over longer distances. Graphene was deposited on a glass surface where it was coated with single layer of membrane, which could then be used to capture specific proteins. The results showed that GIET worked over longer distances (up to 30 nm) than FRET and could be used to study proteins attached to the membrane around graphene. Füllbrunn, Li et al. used it to examine a specific complex of proteins called HOPS, which is linked to multiple diseases, including Ebola, measuring distances between the head or tail of HOPS and the membrane to understand protein shapes. This revealed that HOPS adopts an upright position on membranes and alternates between open and closed shapes. The study of Füllbrunn, Li et al. highlights the ability of GIET to address unanswered questions about the function of protein complexes on membrane surfaces and sheds new light on the structural dynamics of HOPS in living cells. As it allows protein interactions to be studied over much greater distances, GIET could be a powerful new tool for cell biology research. Moreover, graphene is also useful in electron microscopy and both approaches combined could achieve a detailed structural picture of proteins in action.
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Affiliation(s)
- Nadia Füllbrunn
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany.,Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, Osnabrück, Germany
| | - Zehao Li
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany.,Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, Osnabrück, Germany.,College of Life Sciences, Beijing University of Chemical Technology, Beijing, China
| | - Lara Jorde
- Department of Physics, University of Osnabrück, Osnabrück, Germany
| | - Christian P Richter
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany
| | - Rainer Kurre
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany.,Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, Osnabrück, Germany
| | - Lars Langemeyer
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany
| | - Changyuan Yu
- College of Life Sciences, Beijing University of Chemical Technology, Beijing, China
| | - Carola Meyer
- Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, Osnabrück, Germany.,Department of Physics, University of Osnabrück, Osnabrück, Germany
| | - Jörg Enderlein
- 3rd Institute of Physics - Biophysics, Georg August University, Göttingen, Germany.,Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), Georg August University, Göttingen, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany.,Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, Osnabrück, Germany
| | - Jacob Piehler
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany.,Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, Osnabrück, Germany
| | - Changjiang You
- Department of Biology/Chemistry, University of Osnabrück, Osnabrück, Germany.,Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, Osnabrück, Germany
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16
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Ueda S, Tamura N, Mima J. Membrane Tethering Potency of Rab-Family Small GTPases Is Defined by the C-Terminal Hypervariable Regions. Front Cell Dev Biol 2020; 8:577342. [PMID: 33102484 PMCID: PMC7554592 DOI: 10.3389/fcell.2020.577342] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 09/09/2020] [Indexed: 12/12/2022] Open
Abstract
Membrane tethering is a crucial step to determine the spatiotemporal specificity of secretory and endocytic trafficking pathways in all eukaryotic endomembrane systems. Recent biochemical studies by a chemically-defined reconstitution approach reveal that, in addition to the structurally-diverse classic tethering factors such as coiled-coil tethering proteins and multisubunit tethering complexes, Rab-family small GTPases also retain the inherent membrane tethering functions to directly and physically bridge two distinct lipid bilayers by themselves. Although Rab-mediated membrane tethering reactions are fairly efficient and specific in the physiological context, its mechanistic basis is yet to be understood. Here, to explore whether and how the intrinsic tethering potency of Rab GTPases is controlled by their C-terminal hypervariable region (HVR) domains that link the conserved small GTPase domains (G-domains) to membrane anchors at the C-terminus, we quantitatively compared tethering activities of two representative Rab isoforms in humans (Rab5a, Rab4a) and their HVR-deleted mutant forms. Strikingly, deletion of the HVR linker domains enabled both Rab5a and Rab4a isoforms to enhance their intrinsic tethering potency, exhibiting 5- to 50-fold higher initial velocities of tethering for the HVR-deleted mutants than those for the full-length, wild-type Rabs. Furthermore, we revealed that the tethering activity of full-length Rab5a was significantly reduced by the omission of anionic lipids and cholesterol from membrane lipids and, however, membrane tethering driven by HVR-deleted Rab5a mutant was completely insensitive to the headgroup composition of lipids. Reconstituted membrane tethering assays with the C-terminally-truncated mutants of Rab4a further uncovered that the N-terminal residues in the HVR linker, located adjacent to the G-domain, are critical for regulating the intrinsic tethering activity. In conclusion, our current findings establish that the non-conserved, flexible C-terminal HVR linker domains define membrane tethering potency of Rab-family small GTPases through controlling the close attachment of the globular G-domains to membrane surfaces, which confers the active tethering-competent state of the G-domains on lipid bilayers.
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Affiliation(s)
- Sanae Ueda
- Institute for Protein Research, Osaka University, Suita, Japan
| | - Naoki Tamura
- Institute for Protein Research, Osaka University, Suita, Japan
| | - Joji Mima
- Institute for Protein Research, Osaka University, Suita, Japan
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17
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Ungermann C, Kümmel D. Structure of membrane tethers and their role in fusion. Traffic 2019; 20:479-490. [DOI: 10.1111/tra.12655] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 04/26/2019] [Accepted: 05/03/2019] [Indexed: 12/27/2022]
Affiliation(s)
- Christian Ungermann
- Biochemistry Section, Department of Biology/ChemistryUniversity of Osnabrück Osnabrück Germany
- Center for Cellular Nanoanalytics (CellNanOs)University of Osnabrück Osnabrück Germany
| | - Daniel Kümmel
- Biochemistry & Structural Biology Section, Institute of BiochemistryUniversity of Münster Münster Germany
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18
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van der Beek J, Jonker C, van der Welle R, Liv N, Klumperman J. CORVET, CHEVI and HOPS – multisubunit tethers of the endo-lysosomal system in health and disease. J Cell Sci 2019; 132:132/10/jcs189134. [DOI: 10.1242/jcs.189134] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
ABSTRACT
Multisubunit tethering complexes (MTCs) are multitasking hubs that form a link between membrane fusion, organelle motility and signaling. CORVET, CHEVI and HOPS are MTCs of the endo-lysosomal system. They regulate the major membrane flows required for endocytosis, lysosome biogenesis, autophagy and phagocytosis. In addition, individual subunits control complex-independent transport of specific cargoes and exert functions beyond tethering, such as attachment to microtubules and SNARE activation. Mutations in CHEVI subunits lead to arthrogryposis, renal dysfunction and cholestasis (ARC) syndrome, while defects in CORVET and, particularly, HOPS are associated with neurodegeneration, pigmentation disorders, liver malfunction and various forms of cancer. Diseases and phenotypes, however, vary per affected subunit and a concise overview of MTC protein function and associated human pathologies is currently lacking. Here, we provide an integrated overview on the cellular functions and pathological defects associated with CORVET, CHEVI or HOPS proteins, both with regard to their complexes and as individual subunits. The combination of these data provides novel insights into how mutations in endo-lysosomal proteins lead to human pathologies.
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Affiliation(s)
- Jan van der Beek
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute for Biomembranes, Utrecht University, Utrecht 3584 CX, The Netherlands
| | - Caspar Jonker
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute for Biomembranes, Utrecht University, Utrecht 3584 CX, The Netherlands
| | - Reini van der Welle
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute for Biomembranes, Utrecht University, Utrecht 3584 CX, The Netherlands
| | - Nalan Liv
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute for Biomembranes, Utrecht University, Utrecht 3584 CX, The Netherlands
| | - Judith Klumperman
- Section Cell Biology, Center for Molecular Medicine, University Medical Center Utrecht, Institute for Biomembranes, Utrecht University, Utrecht 3584 CX, The Netherlands
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19
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Starr ML, Sparks RP, Arango AS, Hurst LR, Zhao Z, Lihan M, Jenkins JL, Tajkhorshid E, Fratti RA. Phosphatidic acid induces conformational changes in Sec18 protomers that prevent SNARE priming. J Biol Chem 2019; 294:3100-3116. [PMID: 30617180 PMCID: PMC6398130 DOI: 10.1074/jbc.ra118.006552] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 12/31/2018] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic cell homeostasis requires transfer of cellular components among organelles and relies on membrane fusion catalyzed by SNARE proteins. Inactive SNARE bundles are reactivated by hexameric N-ethylmaleimide-sensitive factor, vesicle-fusing ATPase (Sec18/NSF)-driven disassembly that enables a new round of membrane fusion. We previously found that phosphatidic acid (PA) binds Sec18 and thereby sequesters it from SNAREs and that PA dephosphorylation dissociates Sec18 from the membrane, allowing it to engage SNARE complexes. We now report that PA also induces conformational changes in Sec18 protomers and that hexameric Sec18 cannot bind PA membranes. Molecular dynamics (MD) analyses revealed that the D1 and D2 domains of Sec18 contain PA-binding sites and that the residues needed for PA binding are masked in hexameric Sec18. Importantly, these simulations also disclosed that a major conformational change occurs in the linker region between the D1 and D2 domains, which is distinct from the conformational changes that occur in hexameric Sec18 during SNARE priming. Together, these findings indicate that PA regulates Sec18 function by altering its architecture and stabilizing membrane-bound Sec18 protomers.
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Affiliation(s)
- Matthew L Starr
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Robert P Sparks
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Andres S Arango
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Logan R Hurst
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Zhiyu Zhao
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Muyun Lihan
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Jermaine L Jenkins
- the Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, New York 14642
| | - Emad Tajkhorshid
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
- the Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, and
| | - Rutilio A Fratti
- From the Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801,
- the Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
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20
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Starr ML, Fratti RA. The Participation of Regulatory Lipids in Vacuole Homotypic Fusion. Trends Biochem Sci 2018; 44:546-554. [PMID: 30587414 DOI: 10.1016/j.tibs.2018.12.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 11/27/2018] [Accepted: 12/03/2018] [Indexed: 12/28/2022]
Abstract
In eukaryotes, organelles and vesicles modulate their contents and identities through highly regulated membrane fusion events. Membrane trafficking and fusion are carried out through a series of stages that lead to the formation of SNARE complexes between cellular compartment membranes to trigger fusion. Although the protein catalysts of membrane fusion are well characterized, their response to their surrounding microenvironment, provided by the lipid composition of the membrane, remains to be fully understood. Membranes are composed of bulk lipids (e.g., phosphatidylcholine), as well as regulatory lipids that undergo constant modifications by kinases, phosphatases, and lipases. These lipids include phosphoinositides, diacylglycerol, phosphatidic acid, and cholesterol/ergosterol. Here we describe the roles of these lipids throughout the stages of yeast vacuole homotypic fusion.
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Affiliation(s)
- Matthew L Starr
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Rutilio A Fratti
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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21
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Moparthi SB, Wollert T. Reconstruction of destruction – in vitro reconstitution methods in autophagy research. J Cell Sci 2018; 132:132/4/jcs223792. [DOI: 10.1242/jcs.223792] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
ABSTRACT
Autophagy is one of the most elaborative membrane remodeling systems in eukaryotic cells. Its major function is to recycle cytoplasmic material by delivering it to lysosomes for degradation. To achieve this, a membrane cisterna is formed that gradually captures cargo such as organelles or protein aggregates. The diversity of cargo requires autophagy to be highly versatile to adapt the shape of the phagophore to its substrate. Upon closure of the phagophore, a double-membrane-surrounded autophagosome is formed that eventually fuses with lysosomes. In response to environmental cues such as cytotoxicity or starvation, bulk cytoplasm can be captured and delivered to lysosomes. Autophagy thus supports cellular survival under adverse conditions. During the past decades, groundbreaking genetic and cell biological studies have identified the core machinery involved in the process. In this Review, we are focusing on in vitro reconstitution approaches to decipher the details and spatiotemporal control of autophagy, and how such studies contributed to our current understanding of the pathways in yeast and mammals. We highlight studies that revealed the function of the autophagy machinery at a molecular level with respect to its capacity to remodel membranes.
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Affiliation(s)
- Satish Babu Moparthi
- Membrane Biochemistry and Transport, Institute Pasteur, 28 rue du Dr Roux, 75015 Paris, France
| | - Thomas Wollert
- Membrane Biochemistry and Transport, Institute Pasteur, 28 rue du Dr Roux, 75015 Paris, France
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22
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Zhao H, Wang J, Wang T. The V-ATPase V1 subunit A1 is required for rhodopsin anterograde trafficking in Drosophila. Mol Biol Cell 2018; 29:1640-1651. [PMID: 29742016 PMCID: PMC6080656 DOI: 10.1091/mbc.e17-09-0546] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Synthesis and maturation of the light sensor, rhodopsin, are critical for the maintenance of light sensitivity and for photoreceptor homeostasis. In Drosophila, the main rhodopsin, Rh1, is synthesized in the endoplasmic reticulum and transported to the rhabdomere through the secretory pathway. In an unbiased genetic screen for factors involved in rhodopsin homeostasis, we identified mutations in vha68-1, which encodes the vacuolar proton-translocating ATPase (V-ATPase) catalytic subunit A isoform 1 of the V1 component. Loss of vha68-1 in photoreceptor cells disrupted post-Golgi anterograde trafficking of Rh1, reduced light sensitivity, increased secretory vesicle pH, and resulted in incomplete Rh1 deglycosylation. In addition, vha68-1 was required for activity-independent photoreceptor cell survival. Importantly, vha68-1 mutants exhibited phenotypes similar to those exhibited by mutations in the V0 component of V-ATPase, vha100-1. These data demonstrate that the V1 and V0 components of V-ATPase play key roles in post-Golgi trafficking of Rh1 and that Drosophila may represent an important animal model system for studying diseases associated with V-ATPase dysfunction.
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Affiliation(s)
- Haifang Zhao
- School of Life Sciences, Tsinghua University, Beijing 100084, China.,National Institute of Biological Sciences, Beijing 102206, China
| | - Jing Wang
- National Institute of Biological Sciences, Beijing 102206, China
| | - Tao Wang
- National Institute of Biological Sciences, Beijing 102206, China
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23
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Yavuz H, Kattan I, Hernandez JM, Hofnagel O, Witkowska A, Raunser S, Walla PJ, Jahn R. Arrest of trans-SNARE zippering uncovers loosely and tightly docked intermediates in membrane fusion. J Biol Chem 2018; 293:8645-8655. [PMID: 29666192 PMCID: PMC5986196 DOI: 10.1074/jbc.ra118.003313] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Indexed: 12/03/2022] Open
Abstract
Soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) proteins mediate intracellular membrane fusion in the secretory pathway. They contain conserved regions, termed SNARE motifs, that assemble between opposing membranes directionally from their N termini to their membrane-proximal C termini in a highly exergonic reaction. However, how this energy is utilized to overcome the energy barriers along the fusion pathway is still under debate. Here, we have used mutants of the SNARE synaptobrevin to arrest trans-SNARE zippering at defined stages. We have uncovered two distinct vesicle docking intermediates where the membranes are loosely and tightly connected, respectively. The tightly connected state is irreversible and independent of maintaining assembled SNARE complexes. Together, our results shed new light on the intermediate stages along the pathway of membrane fusion.
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Affiliation(s)
| | - Iman Kattan
- Biomolecular Spectroscopy and Single-Molecule Detection Research Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Javier M Hernandez
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Oliver Hofnagel
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | | | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
| | - Peter J Walla
- Biomolecular Spectroscopy and Single-Molecule Detection Research Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.,Biomolecular Spectroscopy and Single-Molecule Detection Research Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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24
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Sparvoli D, Richardson E, Osakada H, Lan X, Iwamoto M, Bowman GR, Kontur C, Bourland WA, Lynn DH, Pritchard JK, Haraguchi T, Dacks JB, Turkewitz AP. Remodeling the Specificity of an Endosomal CORVET Tether Underlies Formation of Regulated Secretory Vesicles in the Ciliate Tetrahymena thermophila. Curr Biol 2018; 28:697-710.e13. [PMID: 29478853 DOI: 10.1016/j.cub.2018.01.047] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Revised: 12/09/2017] [Accepted: 01/17/2018] [Indexed: 12/14/2022]
Abstract
In the endocytic pathway of animals, two related complexes, called CORVET (class C core vacuole/endosome transport) and HOPS (homotypic fusion and protein sorting), act as both tethers and fusion factors for early and late endosomes, respectively. Mutations in CORVET or HOPS lead to trafficking defects and contribute to human disease, including immune dysfunction. HOPS and CORVET are conserved throughout eukaryotes, but remarkably, in the ciliate Tetrahymena thermophila, the HOPS-specific subunits are absent, while CORVET-specific subunits have proliferated. VPS8 (vacuolar protein sorting), a CORVET subunit, expanded to 6 paralogs in Tetrahymena. This expansion correlated with loss of HOPS within a ciliate subgroup, including the Oligohymenophorea, which contains Tetrahymena. As uncovered via forward genetics, a single VPS8 paralog in Tetrahymena (VPS8A) is required to synthesize prominent secretory granules called mucocysts. More specifically, Δvps8a cells fail to deliver a subset of cargo proteins to developing mucocysts, instead accumulating that cargo in vesicles also bearing the mucocyst-sorting receptor Sor4p. Surprisingly, although this transport step relies on CORVET, it does not appear to involve early endosomes. Instead, Vps8a associates with the late endosomal/lysosomal marker Rab7, indicating that target specificity switching occurred in CORVET subunits during the evolution of ciliates. Mucocysts belong to a markedly diverse and understudied class of protist secretory organelles called extrusomes. Our results underscore that biogenesis of mucocysts depends on endolysosomal trafficking, revealing parallels with invasive organelles in apicomplexan parasites and suggesting that a wide array of secretory adaptations in protists, like in animals, depend on mechanisms related to lysosome biogenesis.
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Affiliation(s)
- Daniela Sparvoli
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, USA
| | | | - Hiroko Osakada
- Advanced ICT Research Institute, National Institute of Information and Communications Technology (NICT), Kobe 651-2492, Japan
| | - Xun Lan
- Department of Genetics, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA
| | - Masaaki Iwamoto
- Advanced ICT Research Institute, National Institute of Information and Communications Technology (NICT), Kobe 651-2492, Japan
| | - Grant R Bowman
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, USA
| | - Cassandra Kontur
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, USA
| | - William A Bourland
- Department of Biological Sciences, Boise State University, Boise, ID 83725-1515, USA
| | - Denis H Lynn
- Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Jonathan K Pritchard
- Department of Genetics, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA; Department of Biology, Stanford University, Stanford, CA 94305, USA
| | - Tokuko Haraguchi
- Advanced ICT Research Institute, National Institute of Information and Communications Technology (NICT), Kobe 651-2492, Japan; Graduate School of Frontier Biosciences, Osaka University, Suita 565-0871, Japan
| | - Joel B Dacks
- Department of Cell Biology, University of Alberta, Edmonton, AB T6G 2R3, Canada
| | - Aaron P Turkewitz
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, USA.
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25
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Langemeyer L, Perz A, Kümmel D, Ungermann C. A guanine nucleotide exchange factor (GEF) limits Rab GTPase-driven membrane fusion. J Biol Chem 2017; 293:731-739. [PMID: 29184002 DOI: 10.1074/jbc.m117.812941] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Revised: 11/14/2017] [Indexed: 11/06/2022] Open
Abstract
The identity of organelles in the endomembrane system of any eukaryotic cell critically depends on the correctly localized Rab GTPase, which binds effectors and thus promotes membrane remodeling or fusion. However, it is still unresolved which factors are required and therefore define the localization of the correct fusion machinery. Using SNARE-decorated proteoliposomes that cannot fuse on their own, we now demonstrate that full fusion activity can be achieved by just four soluble factors: a soluble SNARE (Vam7), a guanine nucleotide exchange factor (GEF, Mon1-Ccz1), a Rab-GDP dissociation inhibitor (GDI) complex (prenylated Ypt7-GDI), and a Rab effector complex (HOPS). Our findings reveal that the GEF Mon1-Ccz1 is necessary and sufficient for stabilizing prenylated Ypt7 on membranes. HOPS binding to Ypt7-GTP then drives SNARE-mediated fusion, which is fully GTP-dependent. We conclude that an entire fusion cascade can be controlled by a GEF.
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Affiliation(s)
| | | | - Daniel Kümmel
- Structural Biochemistry, Department of Biology/Chemistry, University of Osnabrück, Barbarastrasse 13, 49076 Osnabrück, Germany
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26
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Inoshita M, Mima J. Human Rab small GTPase- and class V myosin-mediated membrane tethering in a chemically defined reconstitution system. J Biol Chem 2017; 292:18500-18517. [PMID: 28939769 DOI: 10.1074/jbc.m117.811356] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 09/21/2017] [Indexed: 12/13/2022] Open
Abstract
Membrane tethering is a fundamental process essential for the compartmental specificity of intracellular membrane trafficking in eukaryotic cells. Rab-family small GTPases and specific sets of Rab-interacting effector proteins, including coiled-coil tethering proteins and multisubunit tethering complexes, are reported to be responsible for membrane tethering. However, whether and how these key components directly and specifically tether subcellular membranes remains enigmatic. Using chemically defined proteoliposomal systems reconstituted with purified human Rab proteins and synthetic liposomal membranes to study the molecular basis of membrane tethering, we established here that Rab-family GTPases have a highly conserved function to directly mediate membrane tethering, even in the absence of any types of Rab effectors such as the so-called tethering proteins. Moreover, we demonstrate that membrane tethering mediated by endosomal Rab11a is drastically and selectively stimulated by its cognate Rab effectors, class V myosins (Myo5A and Myo5B), in a GTP-dependent manner. Of note, Myo5A and Myo5B exclusively recognized and cooperated with the membrane-anchored form of their cognate Rab11a to support membrane tethering mediated by trans-Rab assemblies on opposing membranes. Our findings support the novel concept that Rab-family proteins provide a bona fide membrane tether to physically and specifically link two distinct lipid bilayers of subcellular membranes. They further indicate that Rab-interacting effector proteins, including class V myosins, can regulate these Rab-mediated membrane-tethering reactions.
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Affiliation(s)
- Motoki Inoshita
- From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Joji Mima
- From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
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27
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Schwartz ML, Nickerson DP, Lobingier BT, Plemel RL, Duan M, Angers CG, Zick M, Merz AJ. Sec17 (α-SNAP) and an SM-tethering complex regulate the outcome of SNARE zippering in vitro and in vivo. eLife 2017; 6:27396. [PMID: 28925353 PMCID: PMC5643095 DOI: 10.7554/elife.27396] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2017] [Accepted: 09/15/2017] [Indexed: 02/02/2023] Open
Abstract
Zippering of SNARE complexes spanning docked membranes is essential for most intracellular fusion events. Here, we explore how SNARE regulators operate on discrete zippering states. The formation of a metastable trans-complex, catalyzed by HOPS and its SM subunit Vps33, is followed by subsequent zippering transitions that increase the probability of fusion. Operating independently of Sec18 (NSF) catalysis, Sec17 (α-SNAP) either inhibits or stimulates SNARE-mediated fusion. If HOPS or Vps33 are absent, Sec17 inhibits fusion at an early stage. Thus, Vps33/HOPS promotes productive SNARE assembly in the presence of otherwise inhibitory Sec17. Once SNAREs are partially zipped, Sec17 promotes fusion in either the presence or absence of HOPS, but with faster kinetics when HOPS is absent, suggesting that ejection of the SM is a rate-limiting step.
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Affiliation(s)
- Matthew L Schwartz
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Daniel P Nickerson
- Department of Biology, California State University, San Bernardino, United States
| | - Braden T Lobingier
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Rachael L Plemel
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Mengtong Duan
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Cortney G Angers
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States
| | - Michael Zick
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Alexey J Merz
- Department of Biochemistry, University of Washington School of Medicine, Seattle, United States.,Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, United States
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28
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Aryal UK, McBride Z, Chen D, Xie J, Szymanski DB. Analysis of protein complexes in Arabidopsis leaves using size exclusion chromatography and label-free protein correlation profiling. J Proteomics 2017. [DOI: 10.1016/j.jprot.2017.06.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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29
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Song H, Orr A, Duan M, Merz AJ, Wickner W. Sec17/Sec18 act twice, enhancing membrane fusion and then disassembling cis-SNARE complexes. eLife 2017; 6:e26646. [PMID: 28718762 PMCID: PMC5540461 DOI: 10.7554/elife.26646] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Accepted: 07/17/2017] [Indexed: 12/17/2022] Open
Abstract
At physiological protein levels, the slow HOPS- and SNARE-dependent fusion which occurs upon complete SNARE zippering is stimulated by Sec17 and Sec18:ATP without requiring ATP hydrolysis. To stimulate, Sec17 needs its central residues which bind the 0-layer of the SNARE complex and its N-terminal apolar loop. Adding a transmembrane anchor to the N-terminus of Sec17 bypasses this requirement for apolarity of the Sec17 loop, suggesting that the loop functions for membrane binding rather than to trigger bilayer rearrangement. In contrast, when complete C-terminal SNARE zippering is prevented, fusion strictly requires Sec18 and Sec17, and the Sec17 apolar loop has functions beyond membrane anchoring. Thus Sec17 and Sec18 act twice in the fusion cycle, binding to trans-SNARE complexes to accelerate fusion, then hydrolyzing ATP to disassemble cis-SNARE complexes.
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Affiliation(s)
- Hongki Song
- Department of Biochemistry and Cell Biology, Geisel School of Medicine, Hanover, United States
| | - Amy Orr
- Department of Biochemistry and Cell Biology, Geisel School of Medicine, Hanover, United States
| | - Mengtong Duan
- Departments of Biochemistry, University of Washington, Seattle, United States
| | - Alexey J Merz
- Departments of Biochemistry, University of Washington, Seattle, United States
- Department of Physiology and Biophysics, University of Washington, Seattle, United States
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine, Hanover, United States
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30
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Song H, Wickner W. A short region upstream of the yeast vacuolar Qa-SNARE heptad-repeats promotes membrane fusion through enhanced SNARE complex assembly. Mol Biol Cell 2017. [PMID: 28637767 PMCID: PMC5555656 DOI: 10.1091/mbc.e17-04-0218] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Membrane fusion requires that four SNARE domains form a complex. A short conserved region just upstream of the Qa-SNARE heptad-repeat domain promotes SNARE-complex assembly and hence fusion. Whereas SNARE (soluble N-ethylmaleimide–sensitive factor attachment protein receptor) heptad-repeats are well studied, SNAREs also have upstream N-domains of indeterminate function. The assembly of yeast vacuolar SNAREs into complexes for fusion can be studied in chemically defined reactions. Complementary proteoliposomes bearing a Rab:GTP and either the vacuolar R-SNARE or one of the three integrally anchored Q-SNAREs were incubated with the tethering/SM protein complex HOPS and the two other soluble SNAREs (lacking a transmembrane anchor) or their SNARE heptad-repeat domains. Fusion required a transmembrane-anchored R-SNARE on one membrane and an anchored Q-SNARE on the other. The N-domain of the Qb-SNARE was completely dispensable for fusion. Whereas fusion can be promoted by very high concentrations of the Qa-SNARE heptad-repeat domain alone, at physiological concentrations the Qa-SNARE heptad-repeat domain alone has almost no fusion activity. The 181–198 region of Qa, immediately upstream of the SNARE heptad-repeat domain, is required for normal fusion activity with HOPS. This region is needed for normal SNARE complex assembly.
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Affiliation(s)
- Hongki Song
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
| | - William Wickner
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755-3844
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31
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Orr A, Song H, Rusin SF, Kettenbach AN, Wickner W. HOPS catalyzes the interdependent assembly of each vacuolar SNARE into a SNARE complex. Mol Biol Cell 2017; 28:975-983. [PMID: 28148647 PMCID: PMC5385945 DOI: 10.1091/mbc.e16-10-0743] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 01/24/2017] [Accepted: 01/27/2017] [Indexed: 11/15/2022] Open
Abstract
Sec1/Munc18 proteins are essential for fusion but of unknown function. The yeast vacuole SM protein is a subunit of the HOPS tethering complex. HOPS catalyzes the interdependent association among the vacuole SNAREs at a membrane surface, and the associated SNAREs can be disassembled by the physiological system Sec17/Sec18/ATP. Rab GTPases, their effectors, SNAREs of the R, Qa, Qb, and Qc families, and SM SNARE-binding proteins catalyze intracellular membrane fusion. At the vacuole/lysosome, they are integrated by the homotypic fusion and vacuole protein sorting (HOPS) complex. Two HOPS subunits bind vacuolar Rabs for tethering, another binds the Qc SNARE, and a fourth HOPS subunit, an SM protein, has conserved grooves that bind R- and Qa-SNARE domains. Spontaneous quaternary SNARE complex assembly is very slow. We report an assay of SNARE complex assembly that does not rely on fusion and for which tethering does not coenrich the four SNAREs. HOPS is required in this assay for rapid SNARE complex assembly. Optimal assembly needs HOPS, lipid membranes to which the R- or Qa-SNARE and Ypt7:GTP are integrally bound, and each of the other three SNAREs. Each SNARE assembles into this complex relying on the others, suggesting four-SNARE complex assembly rather than direct binding of each to HOPS. SNAREs can be disassociated by Sec 17/Sec 18/ATP, completing a catalyzed cycle of SNARE assembly and disassembly.
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Affiliation(s)
- Amy Orr
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - Hongki Song
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - Scott F Rusin
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - Arminja N Kettenbach
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755.,Norris Cotton Cancer Center, Lebanon, NH 03766
| | - William Wickner
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
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32
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Lürick A, Gao J, Kuhlee A, Yavavli E, Langemeyer L, Perz A, Raunser S, Ungermann C. Multivalent Rab interactions determine tether-mediated membrane fusion. Mol Biol Cell 2016; 28:322-332. [PMID: 27852901 PMCID: PMC5231900 DOI: 10.1091/mbc.e16-11-0764] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Accepted: 11/10/2016] [Indexed: 12/22/2022] Open
Abstract
Membrane fusion at endomembranes requires cross-talk between Rab GTPases and tethers to drive SNARE-mediated lipid bilayer mixing. Several tethers have multiple Rab-binding sites with largely untested function. Here we dissected the lysosomal HOPS complex as a tethering complex with just two binding sites for the Rab7-like Ypt7 protein to determine their relevance for fusion. Using tethering and fusion assays combined with HOPS mutants, we show that HOPS-dependent fusion requires both Rab-binding sites, with Vps39 being the stronger Ypt7 interactor than Vps41. The intrinsic amphipathic lipid packaging sensor (ALPS) motif within HOPS Vps41, a target of the vacuolar kinase Yck3, is dispensable for tethering and fusion but can affect tethering if phosphorylated. In combination, our data demonstrate that a multivalent tethering complex uses its two Rab bindings to determine the place of SNARE assembly and thus fusion at endomembranes.
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Affiliation(s)
- Anna Lürick
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Jieqiong Gao
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Anne Kuhlee
- Department of Physical Biochemistry, Max-Planck Institute of Molecular Physiology; 44227 Dortmund, Germany
| | - Erdal Yavavli
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Lars Langemeyer
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Angela Perz
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
| | - Stefan Raunser
- Department of Physical Biochemistry, Max-Planck Institute of Molecular Physiology; 44227 Dortmund, Germany
| | - Christian Ungermann
- Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
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33
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Organelle acidification negatively regulates vacuole membrane fusion in vivo. Sci Rep 2016; 6:29045. [PMID: 27363625 PMCID: PMC4929563 DOI: 10.1038/srep29045] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 06/10/2016] [Indexed: 12/13/2022] Open
Abstract
The V-ATPase is a proton pump consisting of a membrane-integral V0 sector and a peripheral V1 sector, which carries the ATPase activity. In vitro studies of yeast vacuole fusion and evidence from worms, flies, zebrafish and mice suggested that V0 interacts with the SNARE machinery for membrane fusion, that it promotes the induction of hemifusion and that this activity requires physical presence of V0 rather than its proton pump activity. A recent in vivo study in yeast has challenged these interpretations, concluding that fusion required solely lumenal acidification but not the V0 sector itself. Here, we identify the reasons for this discrepancy and reconcile it. We find that acute pharmacological or physiological inhibition of V-ATPase pump activity de-acidifies the vacuole lumen in living yeast cells within minutes. Time-lapse microscopy revealed that de-acidification induces vacuole fusion rather than inhibiting it. Cells expressing mutated V0 subunits that maintain vacuolar acidity were blocked in this fusion. Thus, proton pump activity of the V-ATPase negatively regulates vacuole fusion in vivo. Vacuole fusion in vivo does, however, require physical presence of a fusion-competent V0 sector.
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34
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Abstract
Intracellular membrane fusion is mediated in most cases by membrane-bridging complexes of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). However, the assembly of such complexes in vitro is inefficient, and their uncatalysed disassembly is undetectably slow. Here, we focus on the cellular machinery that orchestrates assembly and disassembly of SNARE complexes, thereby regulating processes ranging from vesicle trafficking to organelle fusion to neurotransmitter release. Rapid progress is being made on many fronts, including the development of more realistic cell-free reconstitutions, the application of single-molecule biophysics, and the elucidation of X-ray and high-resolution electron microscopy structures of the SNARE assembly and disassembly machineries 'in action'.
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Affiliation(s)
- Richard W Baker
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA.,Present address: Department of Cellular and Molecular Medicine, School of Medicine, University of California San Diego, La Jolla, California 92093, USA
| | - Frederick M Hughson
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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35
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Dubuke ML, Munson M. The Secret Life of Tethers: The Role of Tethering Factors in SNARE Complex Regulation. Front Cell Dev Biol 2016; 4:42. [PMID: 27243006 PMCID: PMC4860414 DOI: 10.3389/fcell.2016.00042] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Accepted: 04/25/2016] [Indexed: 02/03/2023] Open
Abstract
Trafficking in eukaryotic cells is a tightly regulated process to ensure correct cargo delivery to the proper destination organelle or plasma membrane. In this review, we focus on how the vesicle fusion machinery, the SNARE complex, is regulated by the interplay of the multisubunit tethering complexes (MTC) with the SNAREs and Sec1/Munc18 (SM) proteins. Although these factors are used in different stages of membrane trafficking, e.g., Golgi to plasma membrane transport vs. vacuolar fusion, and in a variety of diverse eukaryotic cell types, many commonalities between their functions are being revealed. We explore the various protein-protein interactions and findings from functional reconstitution studies in order to highlight both their common features and the differences in their modes of regulation. These studies serve as a starting point for mechanistic explorations in other systems.
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Affiliation(s)
- Michelle L Dubuke
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School Worcester, MA USA
| | - Mary Munson
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School Worcester, MA USA
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36
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Ho R, Stroupe C. The HOPS/class C Vps complex tethers membranes by binding to one Rab GTPase in each apposed membrane. Mol Biol Cell 2015; 26:2655-63. [PMID: 25995379 PMCID: PMC4501362 DOI: 10.1091/mbc.e14-04-0922] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Revised: 05/13/2015] [Accepted: 05/15/2015] [Indexed: 11/30/2022] Open
Abstract
Many Rab GTPase effectors are membrane-tethering factors, that is, they physically link two apposed membranes before intracellular membrane fusion. In this study, we investigate the distinct binding factors needed on apposed membranes for Rab effector-dependent tethering. We show that the homotypic fusion and protein-sorting/class C vacuole protein-sorting (HOPS/class C Vps) complex can tether low-curvature membranes, that is, liposomes with a diameter of ∼100 nm, only when the yeast vacuolar Rab GTPase Ypt7p is present in both tethered membranes. When HOPS is phosphorylated by the vacuolar casein kinase I, Yck3p, tethering only takes place when GTP-bound Ypt7p is present in both tethered membranes. When HOPS is not phosphorylated, however, its tethering activity shows little specificity for the nucleotide-binding state of Ypt7p. These results suggest a model for HOPS-mediated tethering in which HOPS tethers membranes by binding to Ypt7p in each of the two tethered membranes. Moreover, because vacuole-associated HOPS is presumably phosphorylated by Yck3p, our results suggest that nucleotide exchange of Ypt7p on multivesicular bodies (MVBs)/late endosomes must take place before HOPS can mediate tethering at vacuoles.
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Affiliation(s)
- Ruoya Ho
- Department of Molecular Physiology and Biological Physics and Center for Membrane Biology, University of Virginia School of Medicine, Charlottesville, VA 22908
| | - Christopher Stroupe
- Department of Molecular Physiology and Biological Physics and Center for Membrane Biology, University of Virginia School of Medicine, Charlottesville, VA 22908
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37
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Principle of duality in phospholipids: regulators of membrane morphology and dynamics. Biochem Soc Trans 2015; 42:1335-42. [PMID: 25233412 DOI: 10.1042/bst20140224] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
To suggest and develop intelligent strategies to comprehend the regulation of organelle formation, a deeper mechanistic interpretation requires more than just the involvement of proteins. Our approaches link the formation of endomembranes with both signalling and membrane physical properties. Hitherto, membrane morphology, local physical structure and signalling have not been well integrated. Our studies derive from a cross-disciplinary approach undertaken to determine the molecular mechanisms of nuclear envelope assembly in echinoderm and mammalian cells. Our findings have led to the demonstration of a direct role for phosphoinositides and their derivatives in nuclear membrane formation. We have shown that phosphoinositides and their derivatives, as well as acting as second messengers, are modulators of membrane morphology, and their modifying enzymes regulate nuclear envelope formation. In addition, we have shown that echinoderm eggs can be exploited as a milieu to directly study the roles of phospholipids in maintaining organelle shape. The use of the echinoderm egg is a significant step forward in obtaining direct information about membrane physical properties in situ rather than using simpler models which do not provide a complete mechanistic insight into the role of phospholipids in membrane dynamics.
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38
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Numrich J, Péli-Gulli MP, Arlt H, Sardu A, Griffith J, Levine T, Engelbrecht-Vandré S, Reggiori F, De Virgilio C, Ungermann C. The I-BAR protein Ivy1 is an effector of the Rab7 GTPase Ypt7 involved in vacuole membrane homeostasis. J Cell Sci 2015; 128:2278-92. [PMID: 25999476 DOI: 10.1242/jcs.164905] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 05/18/2015] [Indexed: 01/07/2023] Open
Abstract
Membrane fusion at the vacuole depends on a conserved machinery that includes SNAREs, the Rab7 homolog Ypt7 and its effector HOPS. Here, we demonstrate that Ypt7 has an unexpected additional function by controlling membrane homeostasis and nutrient-dependent signaling on the vacuole surface. We show that Ivy1, the yeast homolog of mammalian missing-in-metastasis (MIM), is a vacuolar effector of Ypt7-GTP and interacts with the EGO/ragulator complex, an activator of the target of rapamycin kinase complex 1 (TORC1) on vacuoles. Loss of Ivy1 does not affect EGO vacuolar localization and function. In combination with the deletion of individual subunits of the V-ATPase, however, we observed reduced TORC1 activity and massive enlargement of the vacuole surface. Consistent with this, Ivy1 localizes to invaginations at the vacuole surface and on liposomes in a phosphoinositide- and Ypt7-GTP-controlled manner, which suggests a role in microautophagy. Our data, thus, reveal that Ivy1 is a novel regulator of vacuole membrane homeostasis with connections to TORC1 signaling.
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Affiliation(s)
- Johannes Numrich
- University of Osnabrück, Department of Biology/Chemistry, Biochemistry section, Barbarastrasse 13, 49076 Osnabrück, Germany
| | - Marie-Pierre Péli-Gulli
- University of Fribourg, Department of Biology, Division of Biochemistry, Chemin du Musée 10, Fribourg CH-1700, Switzerland
| | - Henning Arlt
- University of Osnabrück, Department of Biology/Chemistry, Biochemistry section, Barbarastrasse 13, 49076 Osnabrück, Germany
| | - Alessandro Sardu
- University of Fribourg, Department of Biology, Division of Biochemistry, Chemin du Musée 10, Fribourg CH-1700, Switzerland
| | - Janice Griffith
- University Medical Centre Utrecht, Center for Molecular Medicine, Department of Cell Biology, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands
| | - Tim Levine
- UCL Institute of Ophthalmology, Department of Cell Biology, 11-43 Bath St., London EC1V 9EL, UK
| | - Siegfried Engelbrecht-Vandré
- University of Osnabrück, Department of Biology/Chemistry, Biochemistry section, Barbarastrasse 13, 49076 Osnabrück, Germany
| | - Fulvio Reggiori
- University Medical Centre Utrecht, Center for Molecular Medicine, Department of Cell Biology, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands
| | - Claudio De Virgilio
- University of Fribourg, Department of Biology, Division of Biochemistry, Chemin du Musée 10, Fribourg CH-1700, Switzerland
| | - Christian Ungermann
- University of Osnabrück, Department of Biology/Chemistry, Biochemistry section, Barbarastrasse 13, 49076 Osnabrück, Germany
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39
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Kissing S, Hermsen C, Repnik U, Nesset CK, von Bargen K, Griffiths G, Ichihara A, Lee BS, Schwake M, De Brabander J, Haas A, Saftig P. Vacuolar ATPase in phagosome-lysosome fusion. J Biol Chem 2015; 290:14166-80. [PMID: 25903133 DOI: 10.1074/jbc.m114.628891] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Indexed: 01/11/2023] Open
Abstract
The vacuolar H(+)-ATPase (v-ATPase) complex is instrumental in establishing and maintaining acidification of some cellular compartments, thereby ensuring their functionality. Recently it has been proposed that the transmembrane V0 sector of v-ATPase and its a-subunits promote membrane fusion in the endocytic and exocytic pathways independent of their acidification functions. Here, we tested if such a proton-pumping independent role of v-ATPase also applies to phagosome-lysosome fusion. Surprisingly, endo(lyso)somes in mouse embryonic fibroblasts lacking the V0 a3 subunit of the v-ATPase acidified normally, and endosome and lysosome marker proteins were recruited to phagosomes with similar kinetics in the presence or absence of the a3 subunit. Further experiments used macrophages with a knockdown of v-ATPase accessory protein 2 (ATP6AP2) expression, resulting in a strongly reduced level of the V0 sector of the v-ATPase. However, acidification appeared undisturbed, and fusion between latex bead-containing phagosomes and lysosomes, as analyzed by electron microscopy, was even slightly enhanced, as was killing of non-pathogenic bacteria by V0 mutant macrophages. Pharmacologically neutralized lysosome pH did not affect maturation of phagosomes in mouse embryonic cells or macrophages. Finally, locking the two large parts of the v-ATPase complex together by the drug saliphenylhalamide A did not inhibit in vitro and in cellulo fusion of phagosomes with lysosomes. Hence, our data do not suggest a fusion-promoting role of the v-ATPase in the formation of phagolysosomes.
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Affiliation(s)
- Sandra Kissing
- From the Institute of Biochemistry, Christian-Albrechts-University of Kiel, D-24098 Kiel, Germany
| | - Christina Hermsen
- Institute for Cell Biology, Friedrich-Wilhelms University, D-53121 Bonn, Germany
| | - Urska Repnik
- Department of Biosciences, University of Oslo, 0316 Oslo, Norway
| | | | - Kristine von Bargen
- Institute for Cell Biology, Friedrich-Wilhelms University, D-53121 Bonn, Germany
| | - Gareth Griffiths
- Department of Biosciences, University of Oslo, 0316 Oslo, Norway
| | - Atsuhiro Ichihara
- Department of Medicine II, Tokyo Women's Medical University, Tokyo 162-866, Japan
| | - Beth S Lee
- Department of Physiology and Cell Biology, The Ohio State University College of Medicine, Columbus, Ohio 42210
| | - Michael Schwake
- Department of Chemistry, Biochemistry III, University of Bielefeld, D-33615 Bielefeld, Germany, and
| | - Jef De Brabander
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390
| | - Albert Haas
- Institute for Cell Biology, Friedrich-Wilhelms University, D-53121 Bonn, Germany,
| | - Paul Saftig
- From the Institute of Biochemistry, Christian-Albrechts-University of Kiel, D-24098 Kiel, Germany,
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40
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Abstract
Sec17 [soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein; α-SNAP] and Sec18 (NSF) perform ATP-dependent disassembly of cis-SNARE complexes, liberating SNAREs for subsequent assembly of trans-complexes for fusion. A mutant of Sec17, with limited ability to stimulate Sec18, still strongly enhanced fusion when ample Sec18 was supplied, suggesting that Sec17 has additional functions. We used fusion reactions where the four SNAREs were initially separate, thus requiring no disassembly by Sec18. With proteoliposomes bearing asymmetrically disposed SNAREs, tethering and trans-SNARE pairing allowed slow fusion. Addition of Sec17 did not affect the levels of trans-SNARE complex but triggered sudden fusion of trans-SNARE paired proteoliposomes. Sec18 did not substitute for Sec17 in triggering fusion, but ADP- or ATPγS-bound Sec18 enhanced this Sec17 function. The extent of the Sec17 effect varied with the lipid headgroup and fatty acyl composition of the proteoliposomes. Two mutants further distinguished the two Sec17 functions: Sec17(L291A,L292A) did not stimulate Sec18 to disassemble cis-SNARE complex but triggered the fusion of trans-SNARE paired membranes. Sec17(F21S,M22S), with diminished apolar character to its hydrophobic loop, fully supported Sec18-mediated SNARE complex disassembly but had lost the capacity to stimulate the fusion of trans-SNARE paired membranes. To model the interactions of SNARE-bound Sec17 with membranes, we show that Sec17, but not Sec17(F21S,M22S), interacted synergistically with the soluble SNARE domains to enable their stable association with liposomes. We propose a model in which Sec17 binds to trans-SNARE complexes, oligomerizes, and inserts apolar loops into the apposed membranes, locally disturbing the lipid bilayer and thereby lowering the energy barrier for fusion.
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41
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Zhang Y, Diao J, Colbert KN, Lai Y, Pfuetzner RA, Padolina MS, Vivona S, Ressl S, Cipriano DJ, Choi UB, Shah N, Weis WI, Brunger AT. Munc18a does not alter fusion rates mediated by neuronal SNAREs, synaptotagmin, and complexin. J Biol Chem 2015; 290:10518-34. [PMID: 25716318 PMCID: PMC4400359 DOI: 10.1074/jbc.m114.630772] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Indexed: 01/25/2023] Open
Abstract
Sec1/Munc18 (SM) proteins are essential for membrane trafficking, but their molecular mechanism remains unclear. Using a single vesicle-vesicle content-mixing assay with reconstituted neuronal SNAREs, synaptotagmin-1, and complexin-1, we show that the neuronal SM protein Munc18a/nSec1 has no effect on the intrinsic kinetics of both spontaneous fusion and Ca2+-triggered fusion between vesicles that mimic synaptic vesicles and the plasma membrane. However, wild type Munc18a reduced vesicle association ∼50% when the vesicles bearing the t-SNAREs syntaxin-1A and SNAP-25 were preincubated with Munc18 for 30 min. Single molecule experiments with labeled SNAP-25 indicate that the reduction of vesicle association is a consequence of sequestration of syntaxin-1A by Munc18a and subsequent release of SNAP-25 (i.e. Munc18a captures syntaxin-1A via its high affinity interaction). Moreover, a phosphorylation mimic mutant of Munc18a with reduced affinity to syntaxin-1A results in less reduction of vesicle association. In summary, Munc18a does not directly affect fusion, although it has an effect on the t-SNARE complex, depending on the presence of other factors and experimental conditions. Our results suggest that Munc18a primarily acts at the prefusion stage.
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Affiliation(s)
- Yunxiang Zhang
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Jiajie Diao
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Karen N Colbert
- From the Departments of Molecular and Cellular Physiology, Structural Biology, and
| | - Ying Lai
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Richard A Pfuetzner
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Mark S Padolina
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Sandro Vivona
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Susanne Ressl
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and
| | - Daniel J Cipriano
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | - Ucheor B Choi
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
| | | | - William I Weis
- From the Departments of Molecular and Cellular Physiology, Structural Biology, and Photon Science and
| | - Axel T Brunger
- From the Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, and Photon Science and the Howard Hughes Medical Institute, Stanford University, Stanford, California 94305
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42
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Orr A, Wickner W, Rusin SF, Kettenbach AN, Zick M. Yeast vacuolar HOPS, regulated by its kinase, exploits affinities for acidic lipids and Rab:GTP for membrane binding and to catalyze tethering and fusion. Mol Biol Cell 2014; 26:305-15. [PMID: 25411340 PMCID: PMC4294677 DOI: 10.1091/mbc.e14-08-1298] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Acidic lipids act as coreceptors with Ypt7p to bind the HOPS complex to support membrane tethering and fusion. After phosphorylation by the vacuolar kinase Yck3p, phospho-HOPS needs both Ypt7p:GTP and acidic lipids to support fusion. Fusion of yeast vacuoles requires the Rab GTPase Ypt7p, four SNAREs (soluble N-ethylmaleimide–sensitive factor attachment protein receptors), the SNARE disassembly chaperones Sec17p/Sec18p, vacuolar lipids, and the Rab-effector complex HOPS (homotypic fusion and vacuole protein sorting). Two HOPS subunits have direct affinity for Ypt7p. Although vacuolar fusion has been reconstituted with purified components, the functional relationships between individual lipids and Ypt7p:GTP have remained unclear. We now report that acidic lipids function with Ypt7p as coreceptors for HOPS, supporting membrane tethering and fusion. After phosphorylation by the vacuolar kinase Yck3p, phospho-HOPS needs both Ypt7p:GTP and acidic lipids to support fusion.
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Affiliation(s)
- Amy Orr
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - William Wickner
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - Scott F Rusin
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - Arminja N Kettenbach
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755 Norris Cotton Cancer Center, Lebanon, NH 03756
| | - Michael Zick
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
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43
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Abstract
Rab GTPases are master regulators of eukaryotic endomembrane systems, particularly functioning in membrane tethering to confer the directionality of intracellular membrane trafficking. However, how exactly Rab GTPases themselves act upon membrane tethering processes has remained enigmatic. Here, we thoroughly tested seven purified Rab GTPases in human, which localize at the various representative organelles, for their capacity to support membrane tethering in vitro. Strikingly, we found that three specific human Rabs (endoplasmic reticulum/Golgi Rab2a, early endosomal Rab5a, and late endosomal/lysosomal Rab7a) strongly accelerated membrane aggregation of synthetic liposomes even in the absence of any additional components, such as classical tethers, tethering factors, and Rab effectors. This Rab-induced membrane aggregation was a reversible membrane tethering reaction that can be strictly controlled by the membrane recruitment of Rab proteins on both apposing membranes. Thus, our current reconstitution studies establish that membrane-anchored human Rab GTPases are an essential tethering factor to directly mediate membrane tethering events.
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Affiliation(s)
- Naoki Tamura
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Joji Mima
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
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44
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Wandinger-Ness A, Zerial M. Rab proteins and the compartmentalization of the endosomal system. Cold Spring Harb Perspect Biol 2014; 6:a022616. [PMID: 25341920 PMCID: PMC4413231 DOI: 10.1101/cshperspect.a022616;] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Of the approximately 70 human Rab GTPases, nearly three-quarters are involved in endocytic trafficking. Significant plasticity in endosomal membrane transport pathways is closely coupled to receptor signaling and Rab GTPase-regulated scaffolds. Here we review current literature pertaining to endocytic Rab GTPase localizations, functions, and coordination with regulatory proteins and effectors. The roles of Rab GTPases in (1) compartmentalization of the endocytic pathway into early, recycling, late, and lysosomal routes; (2) coordination of individual transport steps from vesicle budding to fusion; (3) effector interactomes; and (4) integration of GTPase and signaling cascades are discussed.
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Affiliation(s)
- Angela Wandinger-Ness
- Department of Pathology MSC08 4640, University of New Mexico HSC, Albuquerque, New Mexico 87131
| | - Marino Zerial
- Max Planck Institute of Molecular and Cell Biology and Genetics, 01307 Dresden, Germany
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45
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Wandinger-Ness A, Zerial M. Rab proteins and the compartmentalization of the endosomal system. Cold Spring Harb Perspect Biol 2014; 6:a022616. [PMID: 25341920 DOI: 10.1101/cshperspect.a022616] [Citation(s) in RCA: 414] [Impact Index Per Article: 41.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Of the approximately 70 human Rab GTPases, nearly three-quarters are involved in endocytic trafficking. Significant plasticity in endosomal membrane transport pathways is closely coupled to receptor signaling and Rab GTPase-regulated scaffolds. Here we review current literature pertaining to endocytic Rab GTPase localizations, functions, and coordination with regulatory proteins and effectors. The roles of Rab GTPases in (1) compartmentalization of the endocytic pathway into early, recycling, late, and lysosomal routes; (2) coordination of individual transport steps from vesicle budding to fusion; (3) effector interactomes; and (4) integration of GTPase and signaling cascades are discussed.
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Affiliation(s)
- Angela Wandinger-Ness
- Department of Pathology MSC08 4640, University of New Mexico HSC, Albuquerque, New Mexico 87131
| | - Marino Zerial
- Max Planck Institute of Molecular and Cell Biology and Genetics, 01307 Dresden, Germany
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46
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Lachmann J, Glaubke E, Moore PS, Ungermann C. The Vps39-like TRAP1 is an effector of Rab5 and likely the missing Vps3 subunit of human CORVET. CELLULAR LOGISTICS 2014; 4:e970840. [PMID: 25750764 DOI: 10.4161/21592780.2014.970840] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 09/25/2014] [Indexed: 12/22/2022]
Abstract
Membrane fusion in the endocytic pathway is mediated by a protein machinery consistent of Rab GTPases, tethering factors and SNAREs. In yeast, the endosomal CORVET and lysosomal HOPS tethering complexes share 4 of their 6 subunits. The 2 additional subunits in each complex - Vps3 and Vps8 for CORVET, and the homologous Vps39 and Vps41 for HOPS - bind directly to Rab5 and Rab7, respectively. In humans, all subunits for HOPS have been described. However, human CORVET remains poorly characterized and a homolog of Vps3 is still missing. Here we characterize 2 previously identified Vps39 isoforms, hVps39-1/hVam6/TLP and hVps39-2/TRAP1, in yeast and HEK293 cells. None of them can compensate the loss of the endogenous yeast Vps39, though the specific interaction of hVps39-1 with the virus-specific LT protein was reproduced. Both human Vps39 proteins show a cytosolic localization in yeast and mammalian cells. However, hVps39-2/TRAP1 strongly co-localizes with co-expressed Rab5 and interacts directly with Rab5-GTP in vitro. We conclude that hVps39-2/TRAP1 is an endosomal protein and an effector of Rab5, suggesting a role of the protein as a subunit of the putative human CORVET complex.
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Affiliation(s)
- Jens Lachmann
- Department of Biology/Chemistry; Biochemistry Section; University of Osnabruck ; Osnabrück, Germany
| | - Elina Glaubke
- Department of Biology/Chemistry; Biochemistry Section; University of Osnabruck ; Osnabrück, Germany
| | - Patrick S Moore
- University of Pittsburgh Cancer Institute; Cancer Virology Program ; Pittsburgh, PA USA
| | - Christian Ungermann
- Department of Biology/Chemistry; Biochemistry Section; University of Osnabruck ; Osnabrück, Germany
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47
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Aryal UK, Xiong Y, McBride Z, Kihara D, Xie J, Hall MC, Szymanski DB. A proteomic strategy for global analysis of plant protein complexes. THE PLANT CELL 2014; 26:3867-82. [PMID: 25293756 PMCID: PMC4247564 DOI: 10.1105/tpc.114.127563] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2014] [Revised: 08/11/2014] [Accepted: 09/18/2014] [Indexed: 05/20/2023]
Abstract
Global analyses of protein complex assembly, composition, and location are needed to fully understand how cells coordinate diverse metabolic, mechanical, and developmental activities. The most common methods for proteome-wide analysis of protein complexes rely on affinity purification-mass spectrometry or yeast two-hybrid approaches. These methods are time consuming and are not suitable for many plant species that are refractory to transformation or genome-wide cloning of open reading frames. Here, we describe the proof of concept for a method allowing simultaneous global analysis of endogenous protein complexes that begins with intact leaves and combines chromatographic separation of extracts from subcellular fractions with quantitative label-free protein abundance profiling by liquid chromatography-coupled mass spectrometry. Applying this approach to the crude cytosolic fraction of Arabidopsis thaliana leaves using size exclusion chromatography, we identified hundreds of cytosolic proteins that appeared to exist as components of stable protein complexes. The reliability of the method was validated by protein immunoblot analysis and comparisons with published size exclusion chromatography data and the masses of known complexes. The method can be implemented with appropriate instrumentation, is applicable to any biological system, and has the potential to be further developed to characterize the composition of protein complexes and measure the dynamics of protein complex localization and assembly under different conditions.
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Affiliation(s)
- Uma K Aryal
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Yi Xiong
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Zachary McBride
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Daisuke Kihara
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907 Department of Computer Science, Purdue University, West Lafayette, Indiana 47907
| | - Jun Xie
- Department of Statistics, Purdue University, West Lafayette, Indiana 47907
| | - Mark C Hall
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Daniel B Szymanski
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907 Department of Agronomy, Purdue University, West Lafayette, Indiana 47907
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48
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Brunet S, Sacher M. Are all multisubunit tethering complexes bona fide tethers? Traffic 2014; 15:1282-7. [PMID: 25048641 DOI: 10.1111/tra.12200] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 07/18/2014] [Accepted: 07/18/2014] [Indexed: 01/15/2023]
Abstract
Since the late 1990s, a number of multisubunit tethering complexes (MTCs) have been described that function in membrane trafficking events: TRAPP I, TRAPP II, TRAPP III, COG, HOPS, CORVET, Dsl1, GARP and exocyst. On the basis of structural and sequence similarities, they have been categorized as complexes associated with tethering containing helical rods (CATCHR) (Dsl1, COG, GARP and exocyst) or non-CATCHR (TRAPP I, II and III, HOPS and CORVET) complexes (Yu IM, Hughson FM. Tethering factors as organizers of intracellular vesicular traffic. Annu Rev Cell Dev Biol 2010;26:137-156). Both acronyms (CATCHR and MTC) imply these complexes tether opposing membranes to facilitate fusion. The main question we will address is: have these complexes been formally demonstrated to function as tethers? If the answer is no, then is it premature or even correct to refer to them as tethers? In this commentary, we will argue that the vast majority of MTCs have not been demonstrated to act as a tether. We propose that a distinction between the terms tether and tethering factor be considered to address this issue.
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Affiliation(s)
- Stephanie Brunet
- Department of Biology, Concordia University, Montreal, Quebec, Canada
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49
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Abstract
Membrane trafficking depends on transport vesicles and carriers docking and fusing with the target organelle for the delivery of cargo. Membrane tethers and small guanosine triphosphatases (GTPases) mediate the docking of transport vesicles/carriers to enhance the efficiency of the subsequent SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-mediated fusion event with the target membrane bilayer. Different classes of membrane tethers and their specific intracellular location throughout the endomembrane system are now well defined. Recent biochemical and structural studies have led to a deeper understanding of the mechanism by which membrane tethers mediate docking of membrane carriers as well as an appreciation of the role of tethers in coordinating the correct SNARE complex and in regulating the organization of membrane compartments. This review will summarize the properties and roles of membrane tethers of both secretory and endocytic systems.
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Affiliation(s)
- Pei Zhi Cheryl Chia
- National Institute of Dental and Craniofacial Research, National Institutes of Health30 Convent Drive, Bethesda, MD 20892-4340USA
| | - Paul A. Gleeson
- The Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute30 Flemington Road, The University of Melbourne, Victoria 3010Australia
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50
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Kümmel D, Ungermann C. Principles of membrane tethering and fusion in endosome and lysosome biogenesis. Curr Opin Cell Biol 2014; 29:61-6. [PMID: 24813801 DOI: 10.1016/j.ceb.2014.04.007] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 04/15/2014] [Accepted: 04/23/2014] [Indexed: 11/29/2022]
Abstract
Endosomes and lysosomes receive cargo via vesicular carriers that arrive along multiple trafficking routes. On both organelles, tethering proteins have been identified that interact specifically with Rab5 on endosomes and Rab7 on late endosomes/lysosomes and that facilitate the SNARE-driven membrane fusion. Even though the structure and stoichiometry of the involved proteins and protein complexes differ strongly, they may operate by similar principles. Within this review, we will provide insights into their common functions and discuss the open questions in the field.
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Affiliation(s)
- Daniel Kümmel
- University of Osnabrück, Department of Biology/Chemistry, Biochemistry Section, Barbarastrasse 13, Osnabrück 49076, Germany.
| | - Christian Ungermann
- University of Osnabrück, Department of Biology/Chemistry, Biochemistry Section, Barbarastrasse 13, Osnabrück 49076, Germany.
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