1
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Ke PY. Molecular Mechanism of Autophagosome-Lysosome Fusion in Mammalian Cells. Cells 2024; 13:500. [PMID: 38534345 DOI: 10.3390/cells13060500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Revised: 03/11/2024] [Accepted: 03/12/2024] [Indexed: 03/28/2024] Open
Abstract
In eukaryotes, targeting intracellular components for lysosomal degradation by autophagy represents a catabolic process that evolutionarily regulates cellular homeostasis. The successful completion of autophagy initiates the engulfment of cytoplasmic materials within double-membrane autophagosomes and subsequent delivery to autolysosomes for degradation by acidic proteases. The formation of autolysosomes relies on the precise fusion of autophagosomes with lysosomes. In recent decades, numerous studies have provided insights into the molecular regulation of autophagosome-lysosome fusion. In this review, an overview of the molecules that function in the fusion of autophagosomes with lysosomes is provided. Moreover, the molecular mechanism underlying how these functional molecules regulate autophagosome-lysosome fusion is summarized.
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Affiliation(s)
- Po-Yuan Ke
- Department of Biochemistry & Molecular Biology, Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan
- Liver Research Center, Chang Gung Memorial Hospital, Taoyuan 33305, Taiwan
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2
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Ishida H, Okashita Y, Ishida H, Hayashi M, Izumi M, Makino A, Bhuiyan NH, van Wijk KJ. GFS9 Affects Piecemeal Autophagy of Plastids in Young Seedlings of Arabidopsis thaliana. PLANT & CELL PHYSIOLOGY 2021; 62:1372-1386. [PMID: 34086965 DOI: 10.1093/pcp/pcab084] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 05/26/2021] [Accepted: 06/04/2021] [Indexed: 06/12/2023]
Abstract
Chloroplasts, and plastids in general, contain abundant protein pools that can be major sources of carbon and nitrogen for recycling. We have previously shown that chloroplasts are partially and sequentially degraded by piecemeal autophagy via the Rubisco-containing body. This degradation occurs during plant development and in response to the environment; however, little is known about the fundamental underlying mechanisms. To discover the mechanisms of piecemeal autophagy of chloroplasts/plastids, we conducted a forward-genetics screen following ethyl-methanesulfonate mutagenesis of an Arabidopsis (Arabidopsis thaliana) transgenic line expressing chloroplast-targeted green fluorescent protein (CT-GFP). This screen allowed us to isolate a mutant, gfs9-5, which hyperaccumulated cytoplasmic bodies labeled with CT-GFP of up to 1.0 μm in diameter in the young seedlings. We termed these structures plastid bodies (PBs). The mutant was defective in a membrane-trafficking factor, green fluorescent seed 9 (GFS9), and PB accumulation in gfs9-5 was promoted by darkness and nutrient deficiency. Transmission electron microscopy indicated that gfs9-5 hyperaccumulated structures corresponding to autophagosomes and PBs. gfs9-5 hyperaccumulated membrane-bound endogenous ATG8 proteins, transgenic yellow fluorescent protein (YFP)-ATG8e proteins and autophagosome-like structures labeled with YFP-ATG8e. The YFP-ATG8e signal was associated with the surface of plastids and their protrusions in gfs9-5. Double mutants of gfs9 and autophagy-defective 5 did not accumulate PBs. In gfs9-5, the YFP-ATG8e proteins and PBs could be delivered to the vacuole and autophagic flux was increased. We discuss a possible connection between GFS9 and autophagy and propose a potential use of gfs9-5 as a new tool to study piecemeal plastid autophagy.
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Affiliation(s)
- Hiroyuki Ishida
- Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki Aza Aoba, Sendai 980-8572, Japan
- School of Integrative Plant Sciences, Section of Plant Biology, Cornell University, Ithaca, NY 14853, USA
| | - Yu Okashita
- Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki Aza Aoba, Sendai 980-8572, Japan
| | - Hiromi Ishida
- Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki Aza Aoba, Sendai 980-8572, Japan
- School of Integrative Plant Sciences, Section of Plant Biology, Cornell University, Ithaca, NY 14853, USA
| | - Makoto Hayashi
- Department of Bioscience, Nagahama Institute of Bioscience and Technology, Tamura 1266, Nagahama, Shiga 526-0829, Japan
| | - Masanori Izumi
- Center for Sustainable Resource Science, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Amane Makino
- Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki Aza Aoba, Sendai 980-8572, Japan
| | - Nazmul H Bhuiyan
- School of Integrative Plant Sciences, Section of Plant Biology, Cornell University, Ithaca, NY 14853, USA
- Eurofins Lancaster Lab PSS, Richmond, VA, USA
| | - Klaas J van Wijk
- School of Integrative Plant Sciences, Section of Plant Biology, Cornell University, Ithaca, NY 14853, USA
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3
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Mima J. Self-assemblies of Rab- and Arf-family small GTPases on lipid bilayers in membrane tethering. Biophys Rev 2021; 13:531-539. [PMID: 34471437 DOI: 10.1007/s12551-021-00819-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 06/30/2021] [Indexed: 12/11/2022] Open
Abstract
Small GTPases of the Ras superfamily, which include Ras-, Rho-, Rab-, Arf-, and Ran-family isoforms, are generally known to function as a nucleotide-dependent molecular switch in eukaryotic cells. In the GTP-loaded forms, they selectively recruit their cognate interacting proteins or protein complexes, termed "effectors," to the cytoplasmic face of subcellular membrane compartments, thereby switching on the downstream effector functions, which are vital for fundamental cellular events, such as cell proliferation, cytoskeletal organization, and intracellular membrane trafficking. Nevertheless, in addition to acting as the classic nucleotide-dependent switches for the effectors, recent studies have uncovered that small GTPases themselves can be self-assembled specifically into homo-dimers or higher-order oligomers on membranes, and these assembly processes are likely responsible for their physiological functions. This Review focuses particularly on the self-assembly processes of Rab- and Arf-family isoforms during membrane tethering, the most critical step to ensure the fidelity of membrane trafficking. A summary of the current experimental evidence for self-assemblies of Rab and Arf small GTPases on lipid bilayers in chemically defined reconstitution system is provided.
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Affiliation(s)
- Joji Mima
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871 Japan
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4
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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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5
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Manandhar SP, Siddiqah IM, Cocca SM, Gharakhanian E. A kinase cascade on the yeast lysosomal vacuole regulates its membrane dynamics: conserved kinase Env7 is phosphorylated by casein kinase Yck3. J Biol Chem 2020; 295:12262-12278. [PMID: 32647006 PMCID: PMC7443493 DOI: 10.1074/jbc.ra119.012346] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 06/02/2020] [Indexed: 01/15/2023] Open
Abstract
Membrane fusion/fission is a highly dynamic and conserved process that responds to intra- and extracellular signals. Whereas the molecular machineries involved in membrane fusion/fission have been dissected, regulation of membrane dynamics remains poorly understood. The lysosomal vacuole of budding yeast (Saccharomyces cerevisiae) has served as a seminal model in studies of membrane dynamics. We have previously established that yeast ENV7 encodes an ortholog of STK16-related kinases that localizes to the vacuolar membrane and downregulates vacuolar membrane fusion. Additionally, we have previously reported that Env7 phosphorylation in vivo depends on YCK3, a gene that encodes a vacuolar membrane casein kinase I (CKI) homolog that nonredundantly functions in fusion regulation. Here, we report that Env7 physically interacts with and is directly phosphorylated by Yck3. We also establish that Env7 vacuole fusion/fission regulation and vacuolar localization are mediated through its Yck3-dependent phosphorylation. Through extensive site-directed mutagenesis, we map phosphorylation to the Env7 C terminus and confirm that Ser-331 is a primary and preferred phosphorylation site. Phospho-deficient Env7 mutants were defective in negative regulation of membrane fusion, increasing the number of prominent vacuoles, whereas a phosphomimetic substitution at Ser-331 increased the number of fragmented vacuoles. Bioinformatics approaches confirmed that Env7 Ser-331 is within a motif that is highly conserved in STK16-related kinases and that it also anchors an SXXS CKI phosphorylation motif (328SRFS331). This study represents the first report on the regulatory mechanism of an STK16-related kinase. It also points to regulation of vacuolar membrane dynamics via a novel Yck3-Env7 kinase cascade.
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Affiliation(s)
- Surya P Manandhar
- Department of Biological Sciences, California State University at Long Beach, Long Beach, California, USA
| | - Ikha M Siddiqah
- Department of Biological Sciences, California State University at Long Beach, Long Beach, California, USA
| | - Stephanie M Cocca
- Department of Biological Sciences, California State University at Long Beach, Long Beach, California, USA
| | - Editte Gharakhanian
- Department of Biological Sciences, California State University at Long Beach, Long Beach, California, USA.
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6
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Sparvoli D, Zoltner M, Cheng CY, Field MC, Turkewitz AP. Diversification of CORVET tethers facilitates transport complexity in Tetrahymena thermophila. J Cell Sci 2020; 133:jcs238659. [PMID: 31964712 PMCID: PMC7033735 DOI: 10.1242/jcs.238659] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 01/03/2020] [Indexed: 12/14/2022] Open
Abstract
In endolysosomal networks, two hetero-hexameric tethers called HOPS and CORVET are found widely throughout eukaryotes. The unicellular ciliate Tetrahymena thermophila possesses elaborate endolysosomal structures, but curiously both it and related protozoa lack the HOPS tether and several other trafficking proteins, while retaining the related CORVET complex. Here, we show that Tetrahymena encodes multiple paralogs of most CORVET subunits, which assemble into six distinct complexes. Each complex has a unique subunit composition and, significantly, shows unique localization, indicating participation in distinct pathways. One pair of complexes differ by a single subunit (Vps8), but have late endosomal versus recycling endosome locations. While Vps8 subunits are thus prime determinants for targeting and functional specificity, determinants exist on all subunits except Vps11. This unprecedented expansion and diversification of CORVET provides a potent example of tether flexibility, and illustrates how 'backfilling' following secondary losses of trafficking genes can provide a mechanism for evolution of new pathways.This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Daniela Sparvoli
- Department of Molecular Genetics and Cell Biology, 920 E 58th Street, The University of Chicago, Chicago, IL, 60637, USA
| | - Martin Zoltner
- School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Chao-Yin Cheng
- Department of Molecular Genetics and Cell Biology, 920 E 58th Street, The University of Chicago, Chicago, IL, 60637, USA
| | - Mark C Field
- School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
- Biology Centre, Institute of Parasitology, Czech Academy of Sciences, 37005 Ceske Budejovice, Czech Republic
| | - Aaron P Turkewitz
- Department of Molecular Genetics and Cell Biology, 920 E 58th Street, The University of Chicago, Chicago, IL, 60637, USA
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7
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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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8
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Segawa K, Tamura N, Mima J. Homotypic and heterotypic trans-assembly of human Rab-family small GTPases in reconstituted membrane tethering. J Biol Chem 2019; 294:7722-7739. [PMID: 30910814 DOI: 10.1074/jbc.ra119.007947] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Revised: 03/07/2019] [Indexed: 11/06/2022] Open
Abstract
Membrane tethering is a highly regulated event occurring during the initial physical contact between membrane-bounded transport carriers and their target subcellular membrane compartments, thereby ensuring the spatiotemporal specificity of intracellular membrane trafficking. Although Rab-family small GTPases and specific Rab-interacting effectors, such as coiled-coil tethering proteins and multisubunit tethering complexes, are known to be involved in membrane tethering, how these protein components directly act upon the tethering event remains enigmatic. Here, using a chemically defined reconstitution system, we investigated the molecular basis of membrane tethering by comprehensively and quantitatively evaluating the intrinsic capacities of 10 representative human Rab-family proteins (Rab1a, -3a, -4a, -5a, -6a, -7a, -9a, -11a, -27a, and -33b) to physically tether two distinct membranes via homotypic and heterotypic Rab-Rab assembly. All of the Rabs tested, except Rab27a, specifically caused homotypic membrane tethering at physiologically relevant Rab densities on membrane surfaces (e.g. Rab/lipid molar ratios of 1:100-1:3,000). Notably, endosomal Rab5a retained its intrinsic potency to drive efficient homotypic tethering even at concentrations below the Rab/lipid ratio of 1:3,000. Comprehensive reconstitution experiments further uncovered that heterotypic combinations of human Rab-family isoforms, including Rab1a/6a, Rab1a/9a, and Rab1a/33b, can directly and selectively mediate membrane tethering. Rab1a and Rab9a in particular synergistically triggered very rapid and efficient membrane tethering reactions through their heterotypic trans-assembly on two opposing membranes. In conclusion, our findings establish that, in the physiological context, homotypic and heterotypic trans-assemblies of Rab-family small GTPases can provide the essential molecular machinery necessary to drive membrane tethering in eukaryotic endomembrane systems.
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Affiliation(s)
- Kazuya Segawa
- From the Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Naoki Tamura
- 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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9
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Spatially Distinct Pools of TORC1 Balance Protein Homeostasis. Mol Cell 2019; 73:325-338.e8. [DOI: 10.1016/j.molcel.2018.10.040] [Citation(s) in RCA: 73] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 10/03/2018] [Accepted: 10/25/2018] [Indexed: 11/19/2022]
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10
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Mima J. Reconstitution of membrane tethering mediated by Rab-family small GTPases. Biophys Rev 2017; 10:543-549. [PMID: 29204879 DOI: 10.1007/s12551-017-0358-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 11/16/2017] [Indexed: 12/18/2022] Open
Abstract
Membrane tethering is one of the most critical steps to determine the spatiotemporal specificity of membrane trafficking, which is the process to selectively transport proteins, lipids, and other biological molecules to the appropriate locations in eukaryotic cells, such as subcellular organelles, the plasma membrane, and the extracellular space. Based on genetic, cell biological, biochemical, and structural studies, Rab-family small GTPases and a number of Rab-interacting proteins (termed Rab effectors), including coiled-coil tethering proteins and multisubunit tethering complexes, have been proposed to be key protein components for membrane tethering. Nevertheless, indeed whether and how Rab GTPases and their specific Rab effectors directly act upon and catalyze membrane tethering still remains enigmatic. By chemically defined reconstitution of membrane tethering from purified Rab-family GTPase proteins and synthetic liposomal membranes, recent studies have revealed the intrinsic potency of Rab-family GTPases to physically and specifically tether two distinct lipid bilayers of liposomal membranes. Experimental evidence from these reconstitution studies support the novel working model in which Rab-family small GTPases act as a bona fide membrane tether for mediating membrane tethering events in eukaryotic membrane trafficking.
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Affiliation(s)
- Joji Mima
- Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan.
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11
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D'Agostino M, Risselada HJ, Lürick A, Ungermann C, Mayer A. A tethering complex drives the terminal stage of SNARE-dependent membrane fusion. Nature 2017; 551:634-638. [PMID: 29088698 DOI: 10.1038/nature24469] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 10/03/2017] [Indexed: 11/09/2022]
Abstract
Membrane fusion in eukaryotic cells mediates the biogenesis of organelles, vesicular traffic between them, and exo- and endocytosis of important signalling molecules, such as hormones and neurotransmitters. Distinct tasks in intracellular membrane fusion have been assigned to conserved protein systems. Tethering proteins mediate the initial recognition and attachment of membranes, whereas SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein complexes are considered as the core fusion engine. SNARE complexes provide mechanical energy to distort membranes and drive them through a hemifusion intermediate towards the formation of a fusion pore. This last step is highly energy-demanding. Here we combine the in vivo and in vitro fusion of yeast vacuoles with molecular simulations to show that tethering proteins are critical for overcoming the final energy barrier to fusion pore formation. SNAREs alone drive vacuoles only into the hemifused state. Tethering proteins greatly increase the volume of SNARE complexes and deform the site of hemifusion, which lowers the energy barrier for pore opening and provides the driving force. Thereby, tethering proteins assume a crucial mechanical role in the terminal stage of membrane fusion that is likely to be conserved at multiple steps of vesicular traffic. We therefore propose that SNAREs and tethering proteins should be considered as a single, non-dissociable device that drives fusion. The core fusion machinery may then be larger and more complex than previously thought.
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Affiliation(s)
- Massimo D'Agostino
- Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland
| | - Herre Jelger Risselada
- Georg-August University, Department of Theoretical Physics, Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany.,Leibniz Institute of Surface Modification, Chemical Department, Permoserstrasse 15, D-04318, Leipzig, Germany
| | - Anna Lürick
- University of Osnabrück, Department of Biology/Chemistry, Barbarastrasse 13, D-49076 Osnabrück, Germany
| | - Christian Ungermann
- University of Osnabrück, Department of Biology/Chemistry, Barbarastrasse 13, D-49076 Osnabrück, Germany
| | - Andreas Mayer
- Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland
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12
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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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13
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López-Berges MS, Arst HN, Pinar M, Peñalva MA. Genetic studies on the physiological role of CORVET in Aspergillus nidulans. FEMS Microbiol Lett 2017; 364:3095991. [PMID: 28379362 DOI: 10.1093/femsle/fnx065] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
CORVET and HOPS are protein complexes mediating the maturation of early endosomes (EEs) into late endosomes (LEs)/vacuoles. These hetero-hexamers share four 'core' components, Vps11, Vps16, Vps18 and Vps33, and differ in two specific subunits, CORVET Vps8 and Vps3 and HOPS Vps39 and Vps41. Whereas ablating HOPS-specific components has minor growth effects, ablating any CORVET constituent severely debilitates Aspergillus nidulans growth, buttressing previous work indicating that maturation of EEs into LEs is physiologically crucial. A genetic screen revealed that impairing the slt cation homeostasis pathway rescues the growth defect resulting from inactivation of the 'core' protein Vps33. Subsequent genetic analyses showed that the defect resulting from lack of any one of the five other CORVET components could similarly be rescued by sltAΔ eliminating the slt regulator SltA. Whereas double deletants lacking functionally non-equivalent components of the CORVET and HOPS complexes are rescued by sltAΔ, those lacking functionally equivalent components are not, suggesting that intermediate 'hybrid' complexes previously detected in yeast are physiologically relevant. vps3Δ, vps8Δ, vps39Δ and vps41Δ result in small vacuoles. This phenotype is remediable by sltAΔ in the case of CORVET-specific, but not in the case of HOPS-specific deletants, indicating that the slt- effect on vacuolar size necessitates HOPS.
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Affiliation(s)
- Manuel S López-Berges
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas CSIC, Ramiro de Maeztu 9, Madrid 28040, Spain
| | - Herbert N Arst
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas CSIC, Ramiro de Maeztu 9, Madrid 28040, Spain.,Section of Microbiology, Imperial College London, Flowers Building, Armstrong Road, London SW7 2AZ, UK
| | - Mario Pinar
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas CSIC, Ramiro de Maeztu 9, Madrid 28040, Spain
| | - Miguel A Peñalva
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas CSIC, Ramiro de Maeztu 9, Madrid 28040, Spain
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14
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Abstract
Platelet dense granules (DGs) are membrane bound compartments that store polyphosphate and small molecules such as ADP, ATP, Ca2+, and serotonin. The release of DG contents plays a central role in platelet aggregation to form a hemostatic plug. Accordingly, congenital deficiencies in the biogenesis of platelet DGs underlie human genetic disorders that cause storage pool disease and manifest with prolonged bleeding. DGs belong to a family of lysosome-related organelles, which also includes melanosomes, the compartments where the melanin pigments are synthesized. These organelles share several characteristics including an acidic lumen and, at least in part, the molecular machinery involved in their biogenesis. As a result, many genes affect both DG and melanosome biogenesis and the corresponding patients present not only with bleeding but also with oculocutaneous albinism. The identification and characterization of such genes has been instrumental in dissecting the pathways responsible for organelle biogenesis. Because the study of melanosome biogenesis has advanced more rapidly, this knowledge has been extrapolated to explain how DGs are produced. However, some progress has recently been made in studying platelet DG biogenesis directly in megakaryocytes and megakaryocytoid cells. DGs originate from an endosomal intermediate compartment, the multivesicular body. Maturation and differentiation into a DG begins when newly synthesized DG-specific proteins are delivered from early/recycling endosomal compartments. The machinery that orchestrates this vesicular trafficking is composed of a combination of both ubiquitous and cell type-specific proteins. Here, we review the current knowledge on DG biogenesis. In particular, we focus on the individual human and murine genes encoding the molecular machinery involved in this process and how their deficiencies result in disease.
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Affiliation(s)
- Andrea L Ambrosio
- a Department of Biochemistry and Molecular Biology , Colorado State University , Fort Collins , Colorado , USA
| | - Santiago M Di Pietro
- a Department of Biochemistry and Molecular Biology , Colorado State University , Fort Collins , Colorado , USA
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15
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Magdeleine M, Gautier R, Gounon P, Barelli H, Vanni S, Antonny B. A filter at the entrance of the Golgi that selects vesicles according to size and bulk lipid composition. eLife 2016; 5. [PMID: 27458799 PMCID: PMC4961469 DOI: 10.7554/elife.16988] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 07/12/2016] [Indexed: 12/22/2022] Open
Abstract
When small phosphatidylcholine liposomes are added to perforated cells, they bind preferentially to the Golgi suggesting an exceptional avidity of this organelle for curved membranes without stereospecific interactions. We show that the cis golgin GMAP-210 accounts for this property. First, the liposome tethering properties of the Golgi resembles that of the amphipathic lipid-packing sensor (ALPS) motif of GMAP-210: both preferred small (radius < 40 nm) liposomes made of monounsaturated but not saturated lipids. Second, reducing GMAP-210 levels or redirecting its ALPS motif to mitochondria decreased liposome capture by the Golgi. Extensive mutagenesis analysis suggests that GMAP-210 tethers authentic transport vesicles via the same mechanism whereby the ALPS motif senses lipid-packing defects at the vesicle surface through its regularly spaced hydrophobic residues. We conclude that the Golgi uses GMAP-210 as a filter to select transport vesicles according to their size and bulk lipid composition. DOI:http://dx.doi.org/10.7554/eLife.16988.001
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Affiliation(s)
- Maud Magdeleine
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d'Azur, Valbonne, France
| | - Romain Gautier
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d'Azur, Valbonne, France
| | - Pierre Gounon
- Centre Commun de Microscopie Appliquée, Université Côte d'Azur, Nice, France
| | - Hélène Barelli
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d'Azur, Valbonne, France
| | - Stefano Vanni
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d'Azur, Valbonne, France
| | - Bruno Antonny
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d'Azur, Valbonne, France
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16
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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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17
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Schroeter S, Beckmann S, Schmitt HD. Coat/Tether Interactions-Exception or Rule? Front Cell Dev Biol 2016; 4:44. [PMID: 27243008 PMCID: PMC4868844 DOI: 10.3389/fcell.2016.00044] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Accepted: 04/25/2016] [Indexed: 12/02/2022] Open
Abstract
Coat complexes are important for cargo selection and vesicle formation. Recent evidence suggests that they may also be involved in vesicle targeting. Tethering factors, which form an initial bridge between vesicles and the target membrane, may bind to coat complexes. In this review, we ask whether these coat/tether interactions share some common mechanisms, or whether they are special adaptations to the needs of very specific transport steps. We compare recent findings in two multisubunit tethering complexes, the Dsl1 complex and the HOPS complex, and put them into context with the TRAPP I complex as a prominent example for coat/tether interactions. We explore where coat/tether interactions are found, compare their function and structure, and comment on a possible evolution from a common ancestor of coats and tethers.
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Affiliation(s)
- Saskia Schroeter
- Neurobiology, Max Planck Institute for Biophysical Chemistry Göttingen, Germany
| | - Sabrina Beckmann
- Neurobiology, Max Planck Institute for Biophysical Chemistry Göttingen, Germany
| | - Hans Dieter Schmitt
- Neurobiology, Max Planck Institute for Biophysical Chemistry Göttingen, Germany
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18
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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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19
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Rao Y, Matscheko N, Wollert T. Autophagy in the test tube: In vitro reconstitution of aspects of autophagosome biogenesis. FEBS J 2016; 283:2034-43. [PMID: 26797728 DOI: 10.1111/febs.13661] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Revised: 12/30/2015] [Accepted: 01/14/2016] [Indexed: 01/02/2023]
Abstract
Autophagy is a versatile recycling pathway that delivers cytoplasmic contents to lysosomal compartments for degradation. It involves the formation of a cup-shaped membrane that expands to capture cargo. After the cargo has been entirely enclosed, the membrane is sealed to generate a double-membrane-enclosed compartment, termed the autophagosome. Depending on the physiological state of the cell, the cargo is selected either specifically or non-specifically. The process involves a highly conserved set of autophagy-related proteins. Reconstitution of their action on model membranes in vitro has contributed tremendously to our understanding of autophagosome biogenesis. This review will focus on various in vitro techniques that have been employed to decipher the function of the autophagic core machinery.
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Affiliation(s)
- Yijian Rao
- Molecular Membrane and Organelle Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Nena Matscheko
- Molecular Membrane and Organelle Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Thomas Wollert
- Molecular Membrane and Organelle Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
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