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Junglas B, Gewehr L, Mernberger L, Schönnenbeck P, Jilly R, Hellmann N, Schneider D, Sachse C. Structural basis for GTPase activity and conformational changes of the bacterial dynamin-like protein SynDLP. Cell Rep 2024; 43:114657. [PMID: 39207903 DOI: 10.1016/j.celrep.2024.114657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Revised: 04/23/2024] [Accepted: 08/02/2024] [Indexed: 09/04/2024] Open
Abstract
SynDLP, a dynamin-like protein (DLP) encoded in the cyanobacterium Synechocystis sp. PCC 6803, has recently been identified to be structurally highly similar to eukaryotic dynamins. To elucidate structural changes during guanosine triphosphate (GTP) hydrolysis, we solved the cryoelectron microscopy (cryo-EM) structures of oligomeric full-length SynDLP after addition of guanosine diphosphate (GDP) at 4.1 Å and GTP at 3.6-Å resolution as well as a GMPPNP-bound dimer structure of a minimal G-domain construct of SynDLP at 3.8-Å resolution. In comparison with what has been seen in the previously resolved apo structure, we found that the G-domain is tilted upward relative to the stalk upon GTP hydrolysis and that the G-domain dimerizes via an additional extended dimerization domain not present in canonical G-domains. When incubated with lipid vesicles, we observed formation of irregular tubular SynDLP assemblies that interact with negatively charged lipids. Here, we provide the structural framework of a series of different functional SynDLP assembly states during GTP turnover.
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Affiliation(s)
- Benedikt Junglas
- Ernst Ruska-Center for Microscopy and Spectroscopy with Electrons (ER-C-3): Structural Biology, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Lucas Gewehr
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, 55128 Mainz, Germany
| | - Lara Mernberger
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, 55128 Mainz, Germany
| | - Philipp Schönnenbeck
- Ernst Ruska-Center for Microscopy and Spectroscopy with Electrons (ER-C-3): Structural Biology, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Ruven Jilly
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, 55128 Mainz, Germany
| | - Nadja Hellmann
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, 55128 Mainz, Germany
| | - Dirk Schneider
- Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, 55128 Mainz, Germany; Institute of Molecular Physiology, Johannes Gutenberg University Mainz, 55128 Mainz, Germany.
| | - Carsten Sachse
- Ernst Ruska-Center for Microscopy and Spectroscopy with Electrons (ER-C-3): Structural Biology, Forschungszentrum Jülich, 52425 Jülich, Germany; Department of Biology, Heinrich Heine University, 40225 Düsseldorf, Germany.
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2
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Liu Y, Hu J, Yan B. Enrichment of ER tubule-derived microsomes by differential centrifugation and immunoprecipitation. BIOPHYSICS REPORTS 2024; 10:61-66. [PMID: 38774354 PMCID: PMC11103718 DOI: 10.52601/bpr.2023.230031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Accepted: 12/15/2023] [Indexed: 05/24/2024] Open
Abstract
The endoplasmic reticulum (ER) is an essential component of the endomembrane system in eukaryotes and plays a crucial role in protein and lipid synthesis, as well as the maintenance of calcium homeostasis. Morphologically, the ER is composed primarily of sheets and tubules. The tubular ER is composed of a network of tubular membrane structures, each with diameters ranging from 30 to 50 nanometers. In recent years, there has been in-depth research on the molecular mechanisms of membrane shaping and membrane fusion of the tubular ER. However, there is still limited understanding of the specific physiological functions of the tubular ER. Here, we report a protocol that combines differential centrifugation and immunoprecipitation to specifically enrich microsomes originating from the tubular ER in yeast. The ER tubule-derived microsomes can be further used for proteomic and lipidomic studies or other biochemical analyses.
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Affiliation(s)
- Yiduo Liu
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Beijing 101408, China
| | - Junjie Hu
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Beijing 101408, China
| | - Bing Yan
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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3
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Shi L, Yang C, Zhang M, Li K, Wang K, Jiao L, Liu R, Wang Y, Li M, Wang Y, Ma L, Hu S, Bian X. Dissecting the mechanism of atlastin-mediated homotypic membrane fusion at the single-molecule level. Nat Commun 2024; 15:2488. [PMID: 38509071 PMCID: PMC10954664 DOI: 10.1038/s41467-024-46919-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 03/13/2024] [Indexed: 03/22/2024] Open
Abstract
Homotypic membrane fusion of the endoplasmic reticulum (ER) is mediated by dynamin-like GTPase atlastin (ATL). This fundamental process relies on GTP-dependent domain rearrangements in the N-terminal region of ATL (ATLcyto), including the GTPase domain and three-helix bundle (3HB). However, its conformational dynamics during the GTPase cycle remain elusive. Here, we combine single-molecule FRET imaging and molecular dynamics simulations to address this conundrum. Different from the prevailing model, ATLcyto can form a loose crossover dimer upon GTP binding, which is tightened by GTP hydrolysis for membrane fusion. Furthermore, the α-helical motif between the 3HB and transmembrane domain, which is embedded in the surface of the lipid bilayer and self-associates in the crossover dimer, is required for ATL function. To recycle the proteins, Pi release, which disassembles the dimer, activates frequent relative movements between the GTPase domain and 3HB, and subsequent GDP dissociation alters the conformational preference of the ATLcyto monomer for entering the next reaction cycle. Finally, we found that two disease-causing mutations affect human ATL1 activity by destabilizing GTP binding-induced loose crossover dimer formation and the membrane-embedded helix, respectively. These results provide insights into ATL-mediated homotypic membrane fusion and the pathological mechanisms of related disease.
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Affiliation(s)
- Lijun Shi
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Frontiers Science Center for Cell Responses, Nankai University, Tianjin, 300071, China
| | - Chenguang Yang
- National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Mingyuan Zhang
- College of Life Sciences, Zhejiang University, Hangzhou, 310027, China
| | - Kangning Li
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Frontiers Science Center for Cell Responses, Nankai University, Tianjin, 300071, China
| | - Keying Wang
- College of Life Sciences, Zhejiang University, Hangzhou, 310027, China
| | - Li Jiao
- College of Life Sciences, Nankai University, Tianjin, 300071, China
| | - Ruming Liu
- College of Life Sciences, Nankai University, Tianjin, 300071, China
| | - Yunyun Wang
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Frontiers Science Center for Cell Responses, Nankai University, Tianjin, 300071, China
| | - Ming Li
- National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yong Wang
- College of Life Sciences, Zhejiang University, Hangzhou, 310027, China.
- The Provincial International Science and Technology Cooperation Base on Engineering Biology, International Campus of Zhejiang University, Haining, 314400, China.
| | - Lu Ma
- National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
| | - Shuxin Hu
- National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
| | - Xin Bian
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Frontiers Science Center for Cell Responses, Nankai University, Tianjin, 300071, China.
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4
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Jang E, Lee M, Yoon SY, Lee SS, Park J, Jin MS, Eom SH, Lee C, Jun Y. Yeast lunapark regulates the formation of trans-Sey1p complexes for homotypic ER membrane fusion. iScience 2023; 26:108386. [PMID: 38025788 PMCID: PMC10679814 DOI: 10.1016/j.isci.2023.108386] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 09/24/2023] [Accepted: 10/30/2023] [Indexed: 12/01/2023] Open
Abstract
The endoplasmic reticulum (ER) consists of the nuclear envelope and a connected peripheral network of tubules and interspersed sheets. The structure of ER tubules is generated and maintained by various proteins, including reticulons, DP1/Yop1p, atlastins, and lunapark. Reticulons and DP1/Yop1p stabilize the high membrane curvature of ER tubules, and atlastins mediate homotypic membrane fusion between ER tubules; however, the exact role of lunapark remains poorly characterized. Here, using isolated yeast ER microsomes and reconstituted proteoliposomes, we directly examined the function of the yeast lunapark Lnp1p for yeast atlastin Sey1p-mediated ER fusion and found that Lnp1p inhibits Sey1p-driven membrane fusion. Furthermore, by using a newly developed assay for monitoring trans-Sey1p complex assembly, a prerequisite for ER fusion, we found that assembly of trans-Sey1p complexes was increased by the deletion of LNP1 and decreased by the overexpression of Lnp1p, indicating that Lnp1p inhibits Sey1p-mediated fusion by interfering with assembly of trans-Sey1p complexes.
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Affiliation(s)
- Eunhong Jang
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Miriam Lee
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - So Young Yoon
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Sang Soo Lee
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Jongseo Park
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Mi Sun Jin
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Soo Hyun Eom
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Changwook Lee
- Department of Biological Sciences, School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea
| | - Youngsoo Jun
- School of Life Sciences, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, Republic of Korea
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5
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Schumann W, Loschwitz J, Reiners J, Degrandi D, Legewie L, Stühler K, Pfeffer K, Poschmann G, Smits SHJ, Strodel B. Integrative modeling of guanylate binding protein dimers. Protein Sci 2023; 32:e4818. [PMID: 37916607 PMCID: PMC10683561 DOI: 10.1002/pro.4818] [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: 05/12/2023] [Revised: 09/27/2023] [Accepted: 09/30/2023] [Indexed: 11/03/2023]
Abstract
Guanylate-binding proteins (GBPs) are essential interferon-γ-activated large GTPases that play a crucial role in host defense against intracellular bacteria and parasites. While their protective functions rely on protein polymerization, our understanding of the structural intricacies of these multimerized states remains limited. To bridge this knowledge gap, we present dimer models for human GBP1 (hGBP1) and murine GBP2 and 7 (mGBP2 and mGBP7) using an integrative approach, incorporating the crystal structure of hGBP1's GTPase domain dimer, crosslinking mass spectrometry, small-angle X-ray scattering, protein-protein docking, and molecular dynamics simulations. Our investigation begins by comparing the protein dynamics of hGBP1, mGBP2, and mGBP7. We observe that the M/E domain in all three proteins exhibits significant mobility and hinge motion, with mGBP7 displaying a slightly less pronounced motion but greater flexibility in its GTPase domain. These dynamic distinctions can be attributed to variations in the sequences of mGBP7 and hGBP1/mGBP2, resulting in different dimerization modes. Unlike hGBP1 and its close ortholog mGBP2, which exclusively dimerize through their GTPase domains, we find that mGBP7 exhibits three equally probable alternative dimer structures. The GTPase domain of mGBP7 is only partially involved in its dimerization, primarily due to an accumulation of negative charge, allowing mGBP7 to dimerize independently of GTP. Instead, mGBP7 exhibits a strong tendency to dimerize in an antiparallel arrangement across its stalks. The results of this work go beyond the sequence-structure-function relationship, as the sequence differences in mGBP7 and mGBP2/hGBP1 do not lead to different structures, but to different protein dynamics and dimerization. The distinct GBP dimer structures are expected to encode specific functions crucial for disrupting pathogen membranes.
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Affiliation(s)
- Wibke Schumann
- Institute of Theoretical and Computational ChemistryHeinrich Heine University DüsseldorfDüsseldorfGermany
- Institute of Biological Information Processing: Structural BiochemistryForschungszentrum JülichJülichGermany
| | - Jennifer Loschwitz
- Institute of Theoretical and Computational ChemistryHeinrich Heine University DüsseldorfDüsseldorfGermany
- Institute of Biological Information Processing: Structural BiochemistryForschungszentrum JülichJülichGermany
| | - Jens Reiners
- Center for Structural StudiesHeinrich Heine University DüsseldorfDüsseldorfGermany
| | - Daniel Degrandi
- Institute of Medical Microbiology and Hospital HygieneHeinrich Heine UniversityDüsseldorfGermany
| | - Larissa Legewie
- Institute of Medical Microbiology and Hospital HygieneHeinrich Heine UniversityDüsseldorfGermany
| | - Kai Stühler
- Institute of Molecular Medicine, Proteome ResearchMedical Faculty and University Hospital Düsseldorf, Heinrich Heine University DüsseldorfDüsseldorfGermany
- Molecular Proteomics Laboratory, Biomedical Research Centre (BMFZ)Heinrich Heine University DüsseldorfDüsseldorfGermany
| | - Klaus Pfeffer
- Institute of Medical Microbiology and Hospital HygieneHeinrich Heine UniversityDüsseldorfGermany
| | - Gereon Poschmann
- Institute of Molecular Medicine, Proteome ResearchMedical Faculty and University Hospital Düsseldorf, Heinrich Heine University DüsseldorfDüsseldorfGermany
| | - Sander H. J. Smits
- Center for Structural StudiesHeinrich Heine University DüsseldorfDüsseldorfGermany
- Institute for BiochemistryHeinrich Heine University DüsseldorfDüsseldorfGermany
| | - Birgit Strodel
- Institute of Theoretical and Computational ChemistryHeinrich Heine University DüsseldorfDüsseldorfGermany
- Institute of Biological Information Processing: Structural BiochemistryForschungszentrum JülichJülichGermany
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6
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Abstract
Atlastins are mechanochemical GTPases that catalyze homotypic fusion of ER tubules. Recent work has demonstrated that tethering and fusion by the three mammalian atlastin paralogs are differentially regulated by their variable N- and C-terminal extensions. These new findings have profound implications for atlastin-mediated homeostasis of the tubular ER network.
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Affiliation(s)
- Shivaani Krishna
- Bay Area Institute of Science, Altos Labs Inc., Redwood City, CA, USA
| | - Marijn G.J. Ford
- Bay Area Institute of Science, Altos Labs Inc., Redwood City, CA, USA
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7
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Kontou A, Herman EK, Field MC, Dacks JB, Koumandou VL. Evolution of factors shaping the endoplasmic reticulum. Traffic 2022; 23:462-473. [PMID: 36040076 PMCID: PMC9804665 DOI: 10.1111/tra.12863] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 06/30/2022] [Accepted: 07/24/2022] [Indexed: 01/09/2023]
Abstract
Endomembrane system compartments are significant elements in virtually all eukaryotic cells, supporting functions including protein synthesis, post-translational modifications and protein/lipid targeting. In terms of membrane area the endoplasmic reticulum (ER) is the largest intracellular organelle, but the origins of proteins defining the organelle and the nature of lineage-specific modifications remain poorly studied. To understand the evolution of factors mediating ER morphology and function we report a comparative genomics analysis of experimentally characterized ER-associated proteins involved in maintaining ER structure. We find that reticulons, REEPs, atlastins, Ufe1p, Use1p, Dsl1p, TBC1D20, Yip3p and VAPs are highly conserved, suggesting an origin at least as early as the last eukaryotic common ancestor (LECA), although many of these proteins possess additional non-ER functions in modern eukaryotes. Secondary losses are common in individual species and in certain lineages, for example lunapark is missing from the Stramenopiles and the Alveolata. Lineage-specific innovations include protrudin, Caspr1, Arl6IP1, p180, NogoR, kinectin and CLIMP-63, which are restricted to the Opisthokonta. Hence, much of the machinery required to build and maintain the ER predates the LECA, but alternative strategies for the maintenance and elaboration of ER shape and function are present in modern eukaryotes. Moreover, experimental investigations for ER maintenance factors in diverse eukaryotes are expected to uncover novel mechanisms.
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Affiliation(s)
- Aspasia Kontou
- Genetics Laboratory, Department of BiotechnologyAgricultural University of AthensAthensGreece
| | - Emily K. Herman
- Division of Infectious Diseases, Department of MedicineUniversity of AlbertaEdmontonAlbertaCanada,Present address:
Department of Agricultural, Food and Nutritional Science, Faculty of Agricultural, Life and Environmental SciencesUniversity of AlbertaEdmontonAlbertaCanada
| | - Mark C. Field
- School of Life SciencesUniversity of DundeeDundeeUK,Biology CentreCzech Academy of SciencesČeské BudějoviceCzech Republic
| | - Joel B. Dacks
- Division of Infectious Diseases, Department of MedicineUniversity of AlbertaEdmontonAlbertaCanada,Biology CentreCzech Academy of SciencesČeské BudějoviceCzech Republic,Centre for Life's Origin and Evolution, Department of Genetics, Evolution and EnvironmentUniversity College of LondonLondonUK
| | - V. Lila Koumandou
- Genetics Laboratory, Department of BiotechnologyAgricultural University of AthensAthensGreece
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8
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Sardar A, Dewangan N, Panda B, Bhowmick D, Tarafdar PK. Lipid and Lipidation in Membrane Fusion. J Membr Biol 2022; 255:691-703. [PMID: 36102950 PMCID: PMC9472184 DOI: 10.1007/s00232-022-00267-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 08/23/2022] [Indexed: 12/24/2022]
Abstract
Membrane fusion plays a lead role in the transport of vesicles, neurotransmission, mitochondrial dynamics, and viral infection. There are fusion proteins that catalyze and regulate the fusion. Interestingly, various types of fusion proteins are present in nature and they possess diverse mechanisms of action. We have highlighted the importance of the functional domains of intracellular heterotypic fusion, homotypic endoplasmic reticulum (ER), homotypic mitochondrial, and type-I viral fusion. During intracellular heterotypic fusion, the SNAREs and four-helix bundle formation are prevalent. Type-I viral fusion is controlled by the membrane destabilizing properties of fusion peptide and six-helix bundle formation. The ER/mitochondrial homotypic fusion is controlled by GTPase activity and the membrane destabilization properties of the amphipathic helix(s). Although the mechanism of action of these fusion proteins is diverse, they have some similarities. In all cases, the lipid composition of the membrane greatly affects membrane fusion. Next, examples of lipidation of the fusion proteins were discussed. We suggest that the fatty acyl hydrophobic tail not only acts as an anchor but may also modulate the energetics of membrane fusion intermediates. Lipidation is also important to design more effective peptide-based fusion inhibitors. Together, we have shown that membrane lipid composition and lipidation are important to modulate membrane fusion.
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Affiliation(s)
- Avijit Sardar
- grid.417960.d0000 0004 0614 7855Indian Institute of Science Education and Research Kolkata, Nadia, Mohanpur, West Bengal 741246 India
| | - Nikesh Dewangan
- grid.417960.d0000 0004 0614 7855Indian Institute of Science Education and Research Kolkata, Nadia, Mohanpur, West Bengal 741246 India
| | - Bishvanwesha Panda
- grid.417960.d0000 0004 0614 7855Indian Institute of Science Education and Research Kolkata, Nadia, Mohanpur, West Bengal 741246 India
| | - Debosmita Bhowmick
- grid.417960.d0000 0004 0614 7855Indian Institute of Science Education and Research Kolkata, Nadia, Mohanpur, West Bengal 741246 India
| | - Pradip K. Tarafdar
- grid.417960.d0000 0004 0614 7855Indian Institute of Science Education and Research Kolkata, Nadia, Mohanpur, West Bengal 741246 India
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9
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A novel insertion mutation in atlastin 1 is associated with spastic quadriplegia, increased membrane tethering, and aberrant conformational switching. J Biol Chem 2021; 298:101438. [PMID: 34808209 PMCID: PMC8688574 DOI: 10.1016/j.jbc.2021.101438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 11/07/2021] [Accepted: 11/17/2021] [Indexed: 11/20/2022] Open
Abstract
Hereditary spastic paraplegia (HSP) comprises a heterogeneous group of neuropathies affecting upper motor neurons and causing progressive gait disorder. Mutations in the gene SPG3A/atlastin-1 (ATL1), encoding a dynamin superfamily member, which utilizes the energy from GTP hydrolysis for membrane tethering and fusion to promote the formation of a highly branched, smooth endoplasmic reticulum (ER), account for approximately 10% of all HSP cases. The continued discovery and characterization of novel disease mutations are crucial for our understanding of HSP pathogenesis and potential treatments. Here, we report a novel disease-causing, in-frame insertion in the ATL1 gene, leading to inclusion of an additional asparagine residue at position 417 (N417ins). This mutation correlates with complex, early-onset spastic quadriplegia affecting all four extremities, generalized dystonia, and a thinning of the corpus callosum. We show using limited proteolysis and FRET-based studies that this novel insertion affects a region in the protein central to intramolecular interactions and GTPase-driven conformational change, and that this insertion mutation is associated with an aberrant prehydrolysis state. While GTPase activity remains unaffected by the insertion, membrane tethering is increased, indicative of a gain-of-function disease mechanism uncommon for ATL1-associated pathologies. In conclusion, our results identify a novel insertion mutation with altered membrane tethering activity that is associated with spastic quadriplegia, potentially uncovering a broad spectrum of molecular mechanisms that may affect neuronal function.
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10
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Chen F, Yan B, Ren J, Lyu R, Wu Y, Guo Y, Li D, Zhang H, Hu J. FIT2 organizes lipid droplet biogenesis with ER tubule-forming proteins and septins. J Cell Biol 2021; 220:211999. [PMID: 33861319 PMCID: PMC8056755 DOI: 10.1083/jcb.201907183] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 12/29/2020] [Accepted: 02/09/2021] [Indexed: 12/20/2022] Open
Abstract
Lipid droplets (LDs) are critical for lipid storage and energy metabolism. LDs form in the endoplasmic reticulum (ER). However, the molecular basis for LD biogenesis remains elusive. Here, we show that fat storage–inducing transmembrane protein 2 (FIT2) interacts with ER tubule-forming proteins Rtn4 and REEP5. The association is mainly transmembrane domain based and stimulated by oleic acid. Depletion of ER tubule-forming proteins decreases the number and size of LDs in cells and Caenorhabditis elegans, mimicking loss of FIT2. Through cytosolic loops, FIT2 binds to cytoskeletal protein septin 7, an interaction that is also required for normal LD biogenesis. Depletion of ER tubule-forming proteins or septins delays nascent LD formation. In addition, FIT2-interacting proteins are up-regulated during adipocyte differentiation, and ER tubule-forming proteins, septin 7, and FIT2 are transiently enriched at LD formation sites. Thus, FIT2-mediated nascent LD biogenesis is facilitated by ER tubule-forming proteins and septins.
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Affiliation(s)
- Fang Chen
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Bing Yan
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Jie Ren
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Rui Lyu
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Yanfang Wu
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Yuting Guo
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Dong Li
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Hong Zhang
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Junjie Hu
- National Laboratory of Biomacromolecules, Chinese Academy of Sciences Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
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11
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O'Donnell JP, Kelly CM, Sondermann H. Nucleotide-Dependent Dimerization and Conformational Switching of Atlastin. Methods Mol Biol 2021; 2159:93-113. [PMID: 32529366 DOI: 10.1007/978-1-0716-0676-6_8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A common feature of dynamin-related proteins (DRPs) is their use of guanosine triphosphate (GTP) to control protein dynamics. In the case of the endoplasmic- reticulum- (ER)-resident membrane protein atlastin (ATL), GTP binding and hydrolysis result in membrane fusion of ER tubules and the generation of a branched ER network. In this chapter, we describe two independent methods for dissecting the mechanism underlying nucleotide-dependent quaternary structure and conformational changes of ATL, focusing on size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) and Förster resonance energy transfer (FRET), respectively. The high temporal resolution of the FRET-based assays enables the ordering of the molecular events identified in structural and equilibrium-based SEC-MALS studies. In combination, these complementary methods report on the oligomeric states of a system at equilibrium and timing of key steps along the enzyme's catalytic cycle. These methods are broadly applicable to proteins that undergo ligand-induced dimerization and/or conformational changes.
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Affiliation(s)
- John P O'Donnell
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
- Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge, UK
| | - Carolyn M Kelly
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA
| | - Holger Sondermann
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA.
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12
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13
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Moon Y, Jun Y. The Effects of Regulatory Lipids on Intracellular Membrane Fusion Mediated by Dynamin-Like GTPases. Front Cell Dev Biol 2020; 8:518. [PMID: 32671068 PMCID: PMC7326814 DOI: 10.3389/fcell.2020.00518] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 06/02/2020] [Indexed: 12/04/2022] Open
Abstract
Membrane fusion mediates a number of fundamental biological processes such as intracellular membrane trafficking, fertilization, and viral infection. Biological membranes are composed of lipids and proteins; while lipids generally play a structural role, proteins mediate specific functions in the membrane. Likewise, although proteins are key players in the fusion of biological membranes, there is emerging evidence supporting a functional role of lipids in various membrane fusion events. Intracellular membrane fusion is mediated by two protein families: SNAREs and membrane-bound GTPases. SNARE proteins are involved in membrane fusion between transport vesicles and their target compartments, as well as in homotypic fusion between organelles of the same type. Membrane-bound GTPases mediate mitochondrial fusion and homotypic endoplasmic reticulum fusion. Certain membrane lipids, known as regulatory lipids, regulate these membrane fusion events by directly affecting the function of membrane-bound GTPases, instead of simply changing the biophysical and biochemical properties of lipid bilayers. In this review, we provide a summary of the current understanding of how regulatory lipids affect GTPase-mediated intracellular membrane fusion by focusing on the functions of regulatory lipids that directly affect fusogenic GTPases.
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Affiliation(s)
- Yeojin Moon
- School of Life Sciences and Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea
| | - Youngsoo Jun
- School of Life Sciences and Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea
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14
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The Dynamin-Like GTPase FgSey1 Plays a Critical Role in Fungal Development and Virulence in Fusarium graminearum. Appl Environ Microbiol 2020; 86:AEM.02720-19. [PMID: 32220839 DOI: 10.1128/aem.02720-19] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2019] [Accepted: 03/16/2020] [Indexed: 12/15/2022] Open
Abstract
Fusarium graminearum, the main pathogenic fungus causing Fusarium head blight (FHB), produces deoxynivalenol (DON), a key virulence factor, which is synthesized in the endoplasmic reticulum (ER). Sey1/atlastin, a dynamin-like GTPase protein, is known to be required for homotypic fusion of ER membranes, but the functions of this protein are unknown in pathogenic fungi. Here, we characterized Sey1/atlastin homologue FgSey1 in F. graminearum Like Sey1/atlastin, FgSey1 is located in the ER. The FgSEY1 deletion mutant exhibited significantly reduced vegetative growth, asexual development, DON biosynthesis, and virulence. Moreover, the ΔFgsey1 mutant was impaired in the formation of normal lipid droplets (LDs) and toxisomes, both of which participate in DON biosynthesis. The GTPase, helix bundle (HB), transmembrane segment (TM), and cytosolic tail (CT) domains of FgSey1 are essential for its function, but only the TM domain is responsible for its localization. Furthermore, the mutants FgSey1K63A and FgSey1T87A lacked GTPase activity and failed to rescue the defects of the ΔFgsey1 mutant. Collectively, our data suggest that the dynamin-like GTPase protein FgSey1 affects the generation of LDs and toxisomes and is required for DON biosynthesis and pathogenesis in F. graminearum IMPORTANCE Fusarium graminearum is a major plant pathogen that causes Fusarium head blight (FHB) of wheats worldwide. In addition to reducing the plant yield, F. graminearum infection of wheats also results in the production of deoxynivalenol (DON) mycotoxins, which are harmful to humans and animals and therefore cause great economic losses through pollution of food products and animal feed. At present, effective strategies for controlling FHB are not available. Therefore, understanding the regulation mechanisms of fungal development, pathogenesis, and DON biosynthesis is important for the development of effective control strategies of this disease. In this study, we demonstrated that a dynamin-like GTPase protein Sey1/atlastin homologue, FgSey1, is required for vegetative growth, DON production, and pathogenicity in F. graminearum Our results provide novel information on critical roles of FgSey1 in fungal pathogenicity; therefore, FgSey1 could be a potential target for effective control of the disease caused by F. graminearum.
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15
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Grimmer M, Bacia K. Giant Endoplasmic Reticulum vesicles (GERVs), a novel model membrane tool. Sci Rep 2020; 10:3100. [PMID: 32080222 PMCID: PMC7033103 DOI: 10.1038/s41598-020-59700-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 01/20/2020] [Indexed: 12/14/2022] Open
Abstract
Artificial giant vesicles have proven highly useful as membrane models in a large variety of biophysical and biochemical studies. They feature accessibility for manipulation and detection, but lack the compositional complexity needed to reconstitute complicated cellular processes. For the plasma membrane (PM), this gap was bridged by the establishment of giant PM vesicles (GPMVs). These native membranes have facilitated studies of protein and lipid diffusion, protein interactions, electrophysiology, fluorescence analysis of lateral domain formation and protein and lipid partitioning as well as mechanical membrane properties and remodeling. The endoplasmic reticulum (ER) is key to a plethora of biological processes in any eukaryotic cell. However, its intracellular location and dynamic and intricate tubular morphology makes it experimentally even less accessible than the PM. A model membrane, which will allow the afore-mentioned types of studies on GPMVs to be performed on ER membranes outside the cell, is therefore genuinely needed. Here, we introduce the formation of giant ER vesicles, termed GERVs, as a new tool for biochemistry and biophysics. To obtain GERVs, we have isolated ER membranes from Saccharomyces cerevisiae and fused them by exploiting the atlastin-like fusion protein Sey1p. We demonstrate the production of GERVs and their utility for further studies.
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Affiliation(s)
- Mona Grimmer
- Biophysical Chemistry, Institute of Chemistry, Charles-Tanford Protein Center, University of Halle, Kurt-Mothes-Str. 3 A, 06120, Halle, Germany
| | - Kirsten Bacia
- Biophysical Chemistry, Institute of Chemistry, Charles-Tanford Protein Center, University of Halle, Kurt-Mothes-Str. 3 A, 06120, Halle, Germany.
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16
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De Vecchis D, Brandner A, Baaden M, Cohen MM, Taly A. A Molecular Perspective on Mitochondrial Membrane Fusion: From the Key Players to Oligomerization and Tethering of Mitofusin. J Membr Biol 2019; 252:293-306. [PMID: 31485701 DOI: 10.1007/s00232-019-00089-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 08/14/2019] [Indexed: 12/29/2022]
Abstract
Mitochondria are dynamic organelles characterized by an ultrastructural organization which is essential in maintaining their quality control and ensuring functional efficiency. The complex mitochondrial network is the result of the two ongoing forces of fusion and fission of inner and outer membranes. Understanding the functional details of mitochondrial dynamics is physiologically relevant as perturbations of this delicate equilibrium have critical consequences and involved in several neurological disorders. Molecular actors involved in this process are large GTPases from the dynamin-related protein family. They catalyze nucleotide-dependent membrane remodeling and are widely conserved from bacteria to higher eukaryotes. Although structural characterization of different family members has contributed in understanding molecular mechanisms of mitochondrial dynamics in more detail, the complete structure of some members as well as the precise assembly of functional oligomers remains largely unknown. As increasing structural data become available, the domain modularity across the dynamin superfamily emerged as a foundation for transfering the knowledge towards less characterized members. In this review, we will first provide an overview of the main actors involved in mitochondrial dynamics. We then discuss recent example of computational methodologies for the study of mitofusin oligomers, and present how the usage of integrative modeling in conjunction with biochemical data can be an asset in progressing the still challenging field of membrane dynamics.
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Affiliation(s)
- Dario De Vecchis
- School of Medicine, Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds, LIGHT Building, Leeds, LS2 9JT, UK.
| | - Astrid Brandner
- CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, 13 Rue Pierre et Marie Curie, 75005, Paris, France.,Institut de Biologie Physico-Chimique - Fondation Edmond de Rothschild, PSL Research University, Paris, France
| | - Marc Baaden
- CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, 13 Rue Pierre et Marie Curie, 75005, Paris, France.,Institut de Biologie Physico-Chimique - Fondation Edmond de Rothschild, PSL Research University, Paris, France
| | - Mickael M Cohen
- Institut de Biologie Physico-Chimique - Fondation Edmond de Rothschild, PSL Research University, Paris, France.,Laboratoire de Biologie Cellulaire et Moléculaire des Eucaryotes, Sorbonne Université, CNRS, UMR 8226, Paris, France
| | - Antoine Taly
- CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, 13 Rue Pierre et Marie Curie, 75005, Paris, France. .,Institut de Biologie Physico-Chimique - Fondation Edmond de Rothschild, PSL Research University, Paris, France.
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17
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Mycobacterial dynamin-like protein IniA mediates membrane fission. Nat Commun 2019; 10:3906. [PMID: 31467269 PMCID: PMC6715688 DOI: 10.1038/s41467-019-11860-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 07/24/2019] [Indexed: 12/13/2022] Open
Abstract
Mycobacterium tuberculosis infection remains a major threat to human health worldwide. Drug treatments against tuberculosis (TB) induce expression of several mycobacterial proteins, including IniA, but its structure and function remain poorly understood. Here, we report the structures of Mycobacterium smegmatis IniA in both the nucleotide-free and GTP-bound states. The structures reveal that IniA folds as a bacterial dynamin-like protein (BDLP) with a canonical GTPase domain followed by two helix-bundles (HBs), named Neck and Trunk. The distal end of its Trunk domain exists as a lipid-interacting (LI) loop, which binds to negatively charged lipids for membrane attachment. IniA does not form detectable nucleotide-dependent dimers in solution. However, lipid tethering indicates nucleotide-independent association of IniA on the membrane. IniA also deforms membranes and exhibits GTP-hydrolyzing dependent membrane fission. These results confirm the membrane remodeling activity of BDLP and suggest that IniA mediates TB drug-resistance through fission activity to maintain plasma membrane integrity.
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18
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Ford MGJ, Chappie JS. The structural biology of the dynamin-related proteins: New insights into a diverse, multitalented family. Traffic 2019; 20:717-740. [PMID: 31298797 DOI: 10.1111/tra.12676] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 07/10/2019] [Accepted: 07/10/2019] [Indexed: 12/13/2022]
Abstract
Dynamin-related proteins are multidomain, mechanochemical GTPases that self-assemble and orchestrate a wide array of cellular processes. Over the past decade, structural insights from X-ray crystallography and cryo-electron microscopy have reshaped our mechanistic understanding of these proteins. Here, we provide a historical perspective on these advances that highlights the structural attributes of different dynamin family members and explores how these characteristics affect GTP hydrolysis, conformational coupling and oligomerization. We also discuss a number of lingering challenges remaining in the field that suggest future directions of study.
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Affiliation(s)
- Marijn G J Ford
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Joshua S Chappie
- Department of Molecular Medicine, Cornell University, Ithaca, New York
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19
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Schoeters F, Van Dijck P. Protein-Protein Interactions in Candida albicans. Front Microbiol 2019; 10:1792. [PMID: 31440220 PMCID: PMC6693483 DOI: 10.3389/fmicb.2019.01792] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 07/19/2019] [Indexed: 12/27/2022] Open
Abstract
Despite being one of the most important human fungal pathogens, Candida albicans has not been studied extensively at the level of protein-protein interactions (PPIs) and data on PPIs are not readily available in online databases. In January 2018, the database called "Biological General Repository for Interaction Datasets (BioGRID)" that contains the most PPIs for C. albicans, only documented 188 physical or direct PPIs (release 3.4.156) while several more can be found in the literature. Other databases such as the String database, the Molecular INTeraction Database (MINT), and the Database for Interacting Proteins (DIP) database contain even fewer interactions or do not even include C. albicans as a searchable term. Because of the non-canonical codon usage of C. albicans where CUG is translated as serine rather than leucine, it is often problematic to use the yeast two-hybrid system in Saccharomyces cerevisiae to study C. albicans PPIs. However, studying PPIs is crucial to gain a thorough understanding of the function of proteins, biological processes and pathways. PPIs can also be potential drug targets. To aid in creating PPI networks and updating the BioGRID, we performed an exhaustive literature search in order to provide, in an accessible format, a more extensive list of known PPIs in C. albicans.
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Affiliation(s)
- Floris Schoeters
- VIB-KU Leuven Center for Microbiology, Leuven, Belgium
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Leuven, Belgium
| | - Patrick Van Dijck
- VIB-KU Leuven Center for Microbiology, Leuven, Belgium
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU Leuven, Leuven, Belgium
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20
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Brandner A, De Vecchis D, Baaden M, Cohen MM, Taly A. Physics-based oligomeric models of the yeast mitofusin Fzo1 at the molecular scale in the context of membrane docking. Mitochondrion 2019; 49:234-244. [PMID: 31306768 DOI: 10.1016/j.mito.2019.06.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 06/07/2019] [Accepted: 06/24/2019] [Indexed: 11/17/2022]
Abstract
Tethering and homotypic fusion of mitochondrial outer membranes is mediated by large GTPases of the dynamin-related proteins family called the mitofusins. The yeast mitofusin Fzo1 forms high molecular weight complexes and its assembly during membrane fusion likely involves the formation of high order complexes. Consistent with this possibility, mitofusins form oligomers in both cis (on the same lipid bilayer) and trans to mediate membrane attachment and fusion. Here, we utilize our recent Fzo1 model to investigate and discuss the formation of cis and trans mitofusin oligomers. We have built three distinct cis-assembly Fzo1 models that gave rise to three distinct trans-oligomeric models of mitofusin constructs. Each model involves two main components of mitofusin oligomerization: the GTPase and the trunk domains. The oligomeric models proposed in this study were further assessed for stability and dynamics in a membrane environment using a coarse-grained molecular dynamics (MD) simulation approach. A narrow opening 'head-to-head' cis-oligomerization (via the GTPase domain) followed by the antiparallel 'back-to-back' trans-associations (via the trunk domain) appears to be in agreement with all of the available experimental data. More broadly, this study opens new possibilities to start exploring cis and trans conformations for Fzo1 and mitofusins in general.
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Affiliation(s)
- Astrid Brandner
- CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, UPR 9080, 13 rue Pierre et Marie Curie, F-75005, Paris, France; Institut de Biologie Physico-Chimique-Fondation Edmond de Rothschild, PSL Research University, Paris, France
| | - Dario De Vecchis
- CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, UPR 9080, 13 rue Pierre et Marie Curie, F-75005, Paris, France; Institut de Biologie Physico-Chimique-Fondation Edmond de Rothschild, PSL Research University, Paris, France
| | - Marc Baaden
- CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, UPR 9080, 13 rue Pierre et Marie Curie, F-75005, Paris, France; Institut de Biologie Physico-Chimique-Fondation Edmond de Rothschild, PSL Research University, Paris, France
| | - Mickael M Cohen
- Laboratoire de Biologie Cellulaire et Moléculaire des Eucaryotes, Sorbonne Université, CNRS, UMR 8226, France; Institut de Biologie Physico-Chimique-Fondation Edmond de Rothschild, PSL Research University, Paris, France.
| | - Antoine Taly
- CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, UPR 9080, 13 rue Pierre et Marie Curie, F-75005, Paris, France; Institut de Biologie Physico-Chimique-Fondation Edmond de Rothschild, PSL Research University, Paris, France.
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21
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Atlastin-mediated membrane tethering is critical for cargo mobility and exit from the endoplasmic reticulum. Proc Natl Acad Sci U S A 2019; 116:14029-14038. [PMID: 31239341 PMCID: PMC6628656 DOI: 10.1073/pnas.1908409116] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
In the early secretory pathway, newly synthesized proteins undergo folding and modifications and then leave the ER through COPII-coated vesicles. How these processes are coordinated and maintained are important but mostly unclear. We show here that ATL, a GTPase that connects ER tubules, controls ER protein mobility and regulates cargo packaging and coat assembly of COPII vesicles. The tethering and fusion activity by ATL likely maintains tension and other necessary parameters for COPII formation in ER membranes. These findings reveal a role of ER shaping in the early secretory pathway and provide insight into behaviors of ER exportation. Endoplasmic reticulum (ER) membrane junctions are formed by the dynamin-like GTPase atlastin (ATL). Deletion of ATL results in long unbranched ER tubules in cells, and mutation of human ATL1 is linked to hereditary spastic paraplegia. Here, we demonstrate that COPII formation is drastically decreased in the periphery of ATL-deleted cells. ER export of cargo proteins becomes defective; ER exit site initiation is not affected, but many of the sites fail to recruit COPII subunits. The efficiency of cargo packaging into COPII vesicles is significantly reduced in cells lacking ATLs, or when the ER is transiently fragmented. Cargo is less mobile in the ER in the absence of ATL, but the cargo mobility and COPII formation can be restored by ATL R77A, which is capable of tethering, but not fusing, ER tubules. These findings suggest that the generation of ER junctions by ATL plays a critical role in maintaining the necessary mobility of ER contents to allow efficient packaging of cargo proteins into COPII vesicles.
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22
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Behrendt L, Kurth I, Kaether C. A disease causing ATLASTIN 3 mutation affects multiple endoplasmic reticulum-related pathways. Cell Mol Life Sci 2019; 76:1433-1445. [PMID: 30666337 PMCID: PMC6420906 DOI: 10.1007/s00018-019-03010-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 01/09/2019] [Accepted: 01/10/2019] [Indexed: 12/01/2022]
Abstract
Atlastins (ATLs) are membrane-bound GTPases involved in shaping of the endoplasmic reticulum (ER). Mutations in ATL1 and ATL3 cause spastic paraplegia and hereditary sensory neuropathy. We here show that the sensory neuropathy causing ATL3 Y192C mutation reduces the complexity of the tubular ER-network. ATL3 Y192C delays ER-export by reducing the number of ER exit sites, reduces autophagy, fragments the Golgi and causes malformation of the nucleus. In cultured primary neurons, ATL3 Y192C does not localize to the growing axon, resulting in axon growth deficits. Patient-derived fibroblasts possess a tubular ER with reduced complexity and have a reduced number of autophagosomes. The data suggest that the disease-causing ATL3 Y192C mutation affects multiple ER-related pathways, possibly as a consequence of the distorted ER morphology.
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Affiliation(s)
- Laura Behrendt
- Leibniz Institut für Alternsforschung-Fritz Lipmann Institut, Beutenbergstr. 11, 07745, Jena, Germany
| | - Ingo Kurth
- Institute of Human Genetics, Medical Faculty, RWTH Aachen University, 52074, Aachen, Germany
| | - Christoph Kaether
- Leibniz Institut für Alternsforschung-Fritz Lipmann Institut, Beutenbergstr. 11, 07745, Jena, Germany.
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23
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Movahed N, Sun J, Vali H, Laliberté JF, Zheng H. A Host ER Fusogen Is Recruited by Turnip Mosaic Virus for Maturation of Viral Replication Vesicles. PLANT PHYSIOLOGY 2019; 179:507-518. [PMID: 30538165 PMCID: PMC6426418 DOI: 10.1104/pp.18.01342] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Accepted: 11/27/2018] [Indexed: 05/23/2023]
Abstract
Like other positive-strand RNA viruses, the Turnip mosaic virus (TuMV) infection leads to the formation of viral vesicles at the endoplasmic reticulum (ER). Once released from the ER, the viral vesicles mature intracellularly and then move intercellularly. While it is known that the membrane-associated viral protein 6K2 plays a role in the process, the contribution of host proteins has been poorly defined. In this article, we show that 6K2 interacts with RHD3, an ER fusogen required for efficient ER fusion. When RHD3 is mutated, a delay in the development of TuMV infection is observed. We found that the replication of TuMV and the cell-to-cell movement of its replication vesicles are impaired in rhd3 This defect can be tracked to a delayed maturation of the viral vesicles from the replication incompetent to the competent state. Furthermore, 6K2 can relocate RHD3 from the ER to viral vesicles. However, a Golgi-localized mutated 6K2GV is unable to interact and relocate RHD3 to viral vesicles. We conclude that the maturation of TuMV replication vesicles requires RHD3 for efficient viral replication and movement.
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Affiliation(s)
- Nooshin Movahed
- Department of Biology, McGill University, Montreal, Quebec, H3A 1B1, Canada
| | - Jiaqi Sun
- Department of Biology, McGill University, Montreal, Quebec, H3A 1B1, Canada
| | - Hojatollah Vali
- Facility for Electron Microscopy Research, McGill University, Montreal, Quebec, H3A 0C7, Canada
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, H3A 0C7, Canada
| | | | - Huanquan Zheng
- Department of Biology, McGill University, Montreal, Quebec, H3A 1B1, Canada
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24
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Wang N, Rapoport TA. Reconstituting the reticular ER network - mechanistic implications and open questions. J Cell Sci 2019; 132:132/4/jcs227611. [PMID: 30670475 DOI: 10.1242/jcs.227611] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The endoplasmic reticulum (ER) is a major membrane-bound organelle in all eukaryotic cells. This organelle comprises morphologically distinct domains, including the nuclear envelope and peripheral sheets and tubules. The tubules are connected by three-way junctions into a network. Several membrane proteins have been implicated in network formation; curvature-stabilizing proteins generate the tubules themselves, and membrane-anchored GTPases fuse tubules into a network. Recent experiments have shown that a tubular network can be formed with reconstituted proteoliposomes containing the yeast membrane-fusing GTPase Sey1 and a curvature-stabilizing protein of either the reticulon or REEP protein families. The network forms in the presence of GTP and is rapidly disassembled when GTP hydrolysis of Sey1 is inhibited, indicating that continuous membrane fusion is required for its maintenance. Atlastin, the ortholog of Sey1 in metazoans, forms a network on its own, serving both as a fusion and curvature-stabilizing protein. These results show that the reticular ER can be generated by a surprisingly small set of proteins, and represents an energy-dependent steady state between formation and disassembly. Models for the molecular mechanism by which curvature-stabilizing proteins cooperate with fusion GTPases to form a reticular network have been proposed, but many aspects remain speculative, including the function of additional proteins, such as the lunapark protein, and the mechanism by which the ER interacts with the cytoskeleton. How the nuclear envelope and peripheral ER sheets are formed remain major unresolved questions in the field. Here, we review reconstitution experiments with purified curvature-stabilizing proteins and fusion GTPases, discuss mechanistic implications and point out open questions.
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Affiliation(s)
- Ning Wang
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Ave, Boston, MA 02115, USA
| | - Tom A Rapoport
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Ave, Boston, MA 02115, USA
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25
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Reciprocal regulation between lunapark and atlastin facilitates ER three-way junction formation. Protein Cell 2018; 10:510-525. [PMID: 30498943 PMCID: PMC6588657 DOI: 10.1007/s13238-018-0595-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 10/23/2018] [Indexed: 11/12/2022] Open
Abstract
Three-way junctions are characteristic structures of the tubular endoplasmic reticulum (ER) network. Junctions are formed through atlastin (ATL)-mediated membrane fusion and stabilized by lunapark (Lnp). However, how Lnp is preferentially enriched at three-way junctions remains elusive. Here, we showed that Lnp loses its junction localization when ATLs are deleted. Reintroduction of ATL1 R77A and ATL3, which have been shown to cluster at the junctions, but not wild-type ATL1, relocates Lnp to the junctions. Mutations in the N-myristoylation site or hydrophobic residues in the coiled coil (CC1) of Lnp N-terminus (NT) cause mis-targeting of Lnp. Conversely, deletion of the lunapark motif in the C-terminal zinc finger domain, which affects the homo-oligomerization of Lnp, does not alter its localization. Purified Lnp-NT attaches to the membrane in a myristoylation-dependent manner. The mutation of hydrophobic residues in CC1 does not affect membrane association, but compromises ATL interactions. In addition, Lnp-NT inhibits ATL-mediated vesicle fusion in vitro. These results suggest that CC1 in Lnp-NT contacts junction-enriched ATLs for proper localization; subsequently, further ATL activity is limited by Lnp after the junction is formed. The proposed mechanism ensures coordinated actions of ATL and Lnp in generating and maintaining three-way junctions.
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26
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Lee M, Moon Y, Lee S, Lee C, Jun Y. Ergosterol interacts with Sey1p to promote atlastin-mediated endoplasmic reticulum membrane fusion in Saccharomyces cerevisiae. FASEB J 2018; 33:3590-3600. [PMID: 30462528 DOI: 10.1096/fj.201800779rr] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Sterols play critical roles in various membrane fusion events, including soluble NSF attachment protein receptor-mediated membrane fusion, mainly by modulating the physical properties of biologic membranes; however, it remains unclear whether they also function in atlastin-mediated endoplasmic reticulum (ER) membrane fusion. Although ergosterol, the major sterol in yeast, is essential for fusion of Sey1p (yeast atlastin)-containing liposomes with an ER-mimicking lipid composition, fusion of phosphatidylcholine/phosphatidylserine liposomes does not require sterols. Here, we examined whether sterols are important for Sey1p-mediated ER fusion in Saccharomyces cerevisiae using an in vitro ER fusion assay with isolated yeast ER microsomes. Ergosterol-specific ligands inhibited microsome fusion, indicating that ergosterol is critical for ER fusion. However, microsomes isolated from yeast strains lacking genes that encode enzymes involved in synthesis of ergosterol from lanosterol still fused, suggesting that other sterols can replace ergosterol and support Sey1p-mediated ER fusion. Importantly, disruption of sterol-binding motifs in the transmembrane regions of Sey1p markedly reduced ER fusion. Sey1p physically interacted with Erg11p and Erg4p, which function in ergosterol biosynthesis, suggesting that Sey1p recruits ergosterol-synthesizing enzymes to fusion sites and thereby enriches ergosterol, which, in turn, may recruit more Sey1p. This positive feedback loop may facilitate ER membrane fusion by concentrating fusion factors at fusion sites.-Lee, M., Moon, Y., Lee, S., Lee, C., Jun, Y. Ergosterol interacts with Sey1p to promote atlastin-mediated endoplasmic reticulum membrane fusion in Saccharomyces cerevisiae.
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Affiliation(s)
- Miriam Lee
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Silver Health Bio Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea
| | - Yeojin Moon
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Silver Health Bio Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea
| | - Sanghwa Lee
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju, South Korea; and
| | - Changwook Lee
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Department of Biological Sciences, School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, South Korea
| | - Youngsoo Jun
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Silver Health Bio Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea.,Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, South Korea
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27
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Winsor J, Machi U, Han Q, Hackney DD, Lee TH. GTP hydrolysis promotes disassembly of the atlastin crossover dimer during ER fusion. J Cell Biol 2018; 217:4184-4198. [PMID: 30249723 PMCID: PMC6279388 DOI: 10.1083/jcb.201805039] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Revised: 08/15/2018] [Accepted: 09/17/2018] [Indexed: 02/06/2023] Open
Abstract
The GTPase atlastin mediates homotypic ER fusion through trans-crossover dimerization, but how dimerization is coupled to the GTPase cycle has remained unclear. Winsor et al. show that GTP binding causes crossover dimerization for fusion, whereas GTP hydrolysis promotes disassembly of the crossover dimer for subunit recycling. Membrane fusion of the ER is catalyzed when atlastin GTPases anchored in opposing membranes dimerize and undergo a crossed over conformational rearrangement that draws the bilayers together. Previous studies have suggested that GTP hydrolysis triggers crossover dimerization, thus directly driving fusion. In this study, we make the surprising observations that WT atlastin undergoes crossover dimerization before hydrolyzing GTP and that nucleotide hydrolysis and Pi release coincide more closely with dimer disassembly. These findings suggest that GTP binding, rather than its hydrolysis, triggers crossover dimerization for fusion. In support, a new hydrolysis-deficient atlastin variant undergoes rapid GTP-dependent crossover dimerization and catalyzes fusion at an initial rate similar to WT atlastin. However, the variant cannot sustain fusion activity over time, implying a defect in subunit recycling. We suggest that GTP binding induces an atlastin conformational change that favors crossover dimerization for fusion and that the input of energy from nucleotide hydrolysis promotes complex disassembly for subunit recycling.
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Affiliation(s)
- James Winsor
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
| | - Ursula Machi
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
| | - Qixiu Han
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
| | - David D Hackney
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
| | - Tina H Lee
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
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28
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Yan L, Qi Y, Huang X, Yu C, Lan L, Guo X, Rao Z, Hu J, Lou Z. Structural basis for GTP hydrolysis and conformational change of MFN1 in mediating membrane fusion. Nat Struct Mol Biol 2018; 25:233-243. [PMID: 29483649 DOI: 10.1038/s41594-018-0034-8] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 01/24/2018] [Indexed: 01/05/2023]
Abstract
Fusion of the outer mitochondrial membrane is mediated by the dynamin-like GTPase mitofusin (MFN). Here, we determined the structure of the minimal GTPase domain (MGD) of human MFN1 in complex with GDP-BeF3-. The MGD folds into a canonical GTPase fold with an associating four-helix bundle, HB1, and forms a dimer. A potassium ion in the catalytic core engages GDP and BeF3- (GDP-BeF3-). Enzymatic analysis has confirmed that efficient GTP hydrolysis by MFN1 requires potassium. Compared to previously reported MGD structures, the HB1 structure undergoes a major conformational change relative to the GTPase domains, as they move from pointing in opposite directions to point in the same direction, suggesting that a swing of the four-helix bundle can pull tethered membranes closer to achieve fusion. The proposed model is supported by results from in vitro biochemical assays and mitochondria morphology rescue assays in MFN1-deleted cells. These findings offer an explanation for how Charcot-Marie-Tooth neuropathy type 2 A (CMT2A)-causing mutations compromise MFN-mediated fusion.
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Affiliation(s)
- Liming Yan
- School of Medicine, Tsinghua University, Beijing, China
| | - Yuanbo Qi
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin, China
| | - Xiaofang Huang
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin, China
| | - Caiting Yu
- School of Medicine, Tsinghua University, Beijing, China
| | - Lan Lan
- National Laboratory of Macromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing, China
| | - Xiangyang Guo
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin, China
| | - Zihe Rao
- School of Medicine, Tsinghua University, Beijing, China.,National Laboratory of Macromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing, China
| | - Junjie Hu
- National Laboratory of Macromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing, China.
| | - Zhiyong Lou
- School of Medicine, Tsinghua University, Beijing, China. .,Collaborative Innovation Center for Biotherapy, Tsinghua University, Tsinghua, China.
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29
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Sun S, Lv L, Yao Z, Bhanot P, Hu J, Wang Q. Identification of endoplasmic reticulum-shaping proteins in Plasmodium parasites. Protein Cell 2018; 7:615-20. [PMID: 27484902 PMCID: PMC4980331 DOI: 10.1007/s13238-016-0290-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Affiliation(s)
- Sha Sun
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin, 300071, China
| | - Li Lv
- Department of Immunology, School of Basic Medical Sciences, Tianjin Medical University, and Tianjin Key Laboratory of Cellular and Molecular Immunology, Tianjin, 300070, China
| | - Zhi Yao
- Department of Immunology, School of Basic Medical Sciences, Tianjin Medical University, and Tianjin Key Laboratory of Cellular and Molecular Immunology, Tianjin, 300070, China
| | - Purnima Bhanot
- Department of Microbiology and Molecular Genetics, Rutgers New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, 07103, USA
| | - Junjie Hu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin, 300071, China
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Qian Wang
- Department of Immunology, School of Basic Medical Sciences, Tianjin Medical University, and Tianjin Key Laboratory of Cellular and Molecular Immunology, Tianjin, 300070, China.
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30
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Stefano G, Brandizzi F. Advances in Plant ER Architecture and Dynamics. PLANT PHYSIOLOGY 2018; 176:178-186. [PMID: 28986423 PMCID: PMC5761816 DOI: 10.1104/pp.17.01261] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 10/01/2017] [Indexed: 05/18/2023]
Abstract
Recent advances highlight mechanisms that enable the morphological integrity of the plant ER in relation to the other organelles and the cytoskeleton.
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Affiliation(s)
- Giovanni Stefano
- MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State University, East Lansing, Michigan 48824
| | - Federica Brandizzi
- MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State University, East Lansing, Michigan 48824
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31
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Sun J, Zheng H. Efficient ER Fusion Requires a Dimerization and a C-Terminal Tail Mediated Membrane Anchoring of RHD3. PLANT PHYSIOLOGY 2018; 176:406-417. [PMID: 29138354 PMCID: PMC5761794 DOI: 10.1104/pp.17.01411] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 11/11/2017] [Indexed: 05/21/2023]
Abstract
The endoplasmic reticulum (ER) is a network of tubules and sheets stretching throughout the eukaryotic cells. The formation of the ER requires homotypic membrane fusion, which is mediated by a family of Dynamin-like Atlastin GTPase proteins. The Arabidopsis (Arabidopsis thaliana) member ROOT HAIR DEFECTIVE3 (RHD3) has been demonstrated to mediate ER membrane fusion, but how exactly RHD3 is involved in the process is still unknown. Here we conducted systemic structure-function analyses of roles of different RHD3 domains in mediating ER fusion. We showed that efficient ER membrane fusion mediated by RHD3 requires a proper dimerization of RHD3 through the GTPase domain (GD) and the first and second three helix bundles (3HBs) in the middle domain. RHD3 has a 3HB-enriched middle domain longer than that of Atlastins, and we revealed that the third and fourth 3HBs are required for the stability of RHD3. The transmembrane segments of RHD3 are essential for targeting and retention of RHD3 in the ER and can also facilitate an oligomerization of RHD3. Furthermore, we showed that an amphipathic helix in the C-terminal cytosolic tail of RHD3 has a membrane anchoring ability that is required for efficient ER membrane fusion mediated by RHD3. This work contributes to a better understanding of a coordinated action of RHD3 in the fusion of ER membranes.
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Affiliation(s)
- Jiaqi Sun
- Department of Biology, McGill University, Montreal, Quebec, H3A 1B1, Canada
| | - Huanquan Zheng
- Department of Biology, McGill University, Montreal, Quebec, H3A 1B1, Canada
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32
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O'Donnell JP, Byrnes LJ, Cooley RB, Sondermann H. A hereditary spastic paraplegia-associated atlastin variant exhibits defective allosteric coupling in the catalytic core. J Biol Chem 2017; 293:687-700. [PMID: 29180453 DOI: 10.1074/jbc.ra117.000380] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 11/17/2017] [Indexed: 11/06/2022] Open
Abstract
The dynamin-related GTPase atlastin (ATL) catalyzes membrane fusion of the endoplasmic reticulum and thus establishes a network of branched membrane tubules. When ATL function is compromised, the morphology of the endoplasmic reticulum deteriorates, and these defects can result in neurological disorders such as hereditary spastic paraplegia and hereditary sensory neuropathy. ATLs harness the energy of GTP hydrolysis to initiate a series of conformational changes that enable homodimerization and subsequent membrane fusion. Disease-associated amino acid substitutions cluster in regions adjacent to ATL's catalytic site, but the consequences for the GTPase's molecular mechanism are often poorly understood. Here, we elucidate structural and functional defects of an atypical hereditary spastic paraplegia mutant, ATL1-F151S, that is impaired in its nucleotide-hydrolysis cycle but can still adopt a high-affinity homodimer when bound to a transition-state analog. Crystal structures of mutant proteins yielded models of the monomeric pre- and post-hydrolysis states of ATL. Together, these findings define a mechanism for allosteric coupling in which Phe151 is the central residue in a hydrophobic interaction network connecting the active site to an interdomain interface responsible for nucleotide loading.
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Affiliation(s)
- John P O'Donnell
- From the Department of Molecular Medicine, Cornell University, Ithaca, New York 14853
| | - Laura J Byrnes
- From the Department of Molecular Medicine, Cornell University, Ithaca, New York 14853
| | - Richard B Cooley
- From the Department of Molecular Medicine, Cornell University, Ithaca, New York 14853
| | - Holger Sondermann
- From the Department of Molecular Medicine, Cornell University, Ithaca, New York 14853
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33
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Sequences flanking the transmembrane segments facilitate mitochondrial localization and membrane fusion by mitofusin. Proc Natl Acad Sci U S A 2017; 114:E9863-E9872. [PMID: 29093165 PMCID: PMC5699052 DOI: 10.1073/pnas.1708782114] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Mitochondria constantly connect through membrane fusion. The merging of the outer mitochondrial membrane requires mitofusin (MFN) proteins. MFN is a membrane-anchored GTPase, but whether it is sufficient to achieve fusion, and if so how, is largely unknown. We have taken advantage of a similar GTPase named atlastin (ATL), which mediates fusion of the endoplasmic reticulum (ER), as its mechanism is better understood. Domain swapping experiments show that MFN is capable of fusing membranes, even on the ER. The C-terminal tail of MFN contains an amphipathic helix that promotes fusion. MFN is properly inserted into the mitochondrial membrane with the help of the helix and neighboring hydrophobic residues. These findings provide insight into how mitochondria fuse. Mitochondria constantly divide and fuse. Homotypic fusion of the outer mitochondrial membranes requires the mitofusin (MFN) proteins, a family of dynamin-like GTPases. MFNs are anchored in the membrane by transmembrane (TM) segments, exposing both the N-terminal GTPase domain and the C-terminal tail (CT) to the cytosol. This arrangement is very similar to that of the atlastin (ATL) GTPases, which mediate fusion of endoplasmic reticulum (ER) membranes. We engineered various MFN-ATL chimeras to gain mechanistic insight into MFN-mediated fusion. When MFN1 is localized to the ER by TM swapping with ATL1, it functions in the maintenance of ER morphology and fusion. In addition, an amphipathic helix in the CT of MFN1 is exchangeable with that of ATL1 and critical for mitochondrial localization of MFN1. Furthermore, hydrophobic residues N-terminal to the TM segments of MFN1 play a role in membrane targeting but not fusion. Our findings provide important insight into MFN-mediated membrane fusion.
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34
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A membrane-inserted structural model of the yeast mitofusin Fzo1. Sci Rep 2017; 7:10217. [PMID: 28860650 PMCID: PMC5578988 DOI: 10.1038/s41598-017-10687-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Accepted: 08/14/2017] [Indexed: 01/23/2023] Open
Abstract
Mitofusins are large transmembrane GTPases of the dynamin-related protein family, and are required for the tethering and fusion of mitochondrial outer membranes. Their full-length structures remain unknown, which is a limiting factor in the study of outer membrane fusion. We investigated the structure and dynamics of the yeast mitofusin Fzo1 through a hybrid computational and experimental approach, combining molecular modelling and all-atom molecular dynamics simulations in a lipid bilayer with site-directed mutagenesis and in vivo functional assays. The predicted architecture of Fzo1 improves upon the current domain annotation, with a precise description of the helical spans linked by flexible hinges, which are likely of functional significance. In vivo site-directed mutagenesis validates salient aspects of this model, notably, the long-distance contacts and residues participating in hinges. GDP is predicted to interact with Fzo1 through the G1 and G4 motifs of the GTPase domain. The model reveals structural determinants critical for protein function, including regions that may be involved in GTPase domain-dependent rearrangements.
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35
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Molecular mechanisms of atlastin-mediated ER membrane fusion revealed by a FRET-based single-vesicle fusion assay. Sci Rep 2017; 7:8700. [PMID: 28821793 PMCID: PMC5562884 DOI: 10.1038/s41598-017-09162-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 07/21/2017] [Indexed: 01/19/2023] Open
Abstract
Homotypic fusion of endoplasmic reticulum membranes is driven by atlastin GTPases; however, the underlying mechanism remains largely unknown. Here, using a FRET-based single-vesicle fusion assay with liposomes bearing the yeast atlastin Sey1p, we investigated the molecular mechanisms of atlastin-mediated membrane tethering and fusion. Although Sey1p-bearing proteoliposomes frequently underwent membrane tethering in a GTP hydrolysis-dependent manner as reported in studies using bulk assays, only a small fraction of the tethered liposomes proceeded to fusion. Strikingly, the rest of the tethered liposomes failed to fuse or dissociate. This stable tethering, however, did not require continued GTP hydrolysis because GTP omission and magnesium chelation did not disrupt tethering. Interestingly, an increased Sey1p density on the membrane markedly accelerated tethering but barely affected the fusion rate of the tethered liposomes, indicating that Sey1p requires additional factors to support efficient fusion in vivo. Finally, the assay also revealed that Sey1p-mediated liposome fusion occurs through hemifusion, suggesting the mechanistic conservation between biological membrane fusion events despite the existence of diverse fusogens.
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36
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Timing and Reset Mechanism of GTP Hydrolysis-Driven Conformational Changes of Atlastin. Structure 2017; 25:997-1010.e4. [PMID: 28602821 DOI: 10.1016/j.str.2017.05.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Revised: 04/12/2017] [Accepted: 05/10/2017] [Indexed: 01/09/2023]
Abstract
The endoplasmic reticulum (ER) forms a branched, dynamic membrane tubule network that is vital for cellular function. Branching arises from membrane fusion facilitated by the GTPase atlastin (ATL). Many metazoan genomes encode for three ATL isoforms that appear to fulfill partially redundant function despite differences in their intrinsic GTPase activity and localization within the ER; however, the underlying mechanistic differences between the isoforms are poorly understood. Here, we identify discrete temporal steps in the catalytic cycle for the two most dissimilar isoforms, ATL1 and ATL3, revealing an overall conserved progression of molecular events from nucleotide binding and hydrolysis to ATL dimerization and phosphate release. A crystal structure of ATL3 suggests a mechanism for the displacement of the catalytic Mg2+ ion following guanosine triphosphate (GTP) hydrolysis. Together, the data extend the mechanistic framework for how GTP hydrolysis drives conformational changes in ATL and how the cycle is reset for subsequent rounds of catalysis.
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37
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Qi Y, Yan L, Yu C, Guo X, Zhou X, Hu X, Huang X, Rao Z, Lou Z, Hu J. Structures of human mitofusin 1 provide insight into mitochondrial tethering. J Cell Biol 2017; 215:621-629. [PMID: 27920125 PMCID: PMC5147005 DOI: 10.1083/jcb.201609019] [Citation(s) in RCA: 130] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2016] [Revised: 10/02/2016] [Accepted: 10/18/2016] [Indexed: 11/26/2022] Open
Abstract
Mitofusin 1 (MFN1) mediates mitochondrial fusion, but the mechanisms involved are unclear. Qi et al. present the crystal structures of a minimal GTPase domain of human MFN1, which suggest that MFN1 tethers apposing membranes through nucleotide-dependent dimerization. Mitochondria undergo fusion and fission. The merging of outer mitochondrial membranes requires mitofusin (MFN), a dynamin-like GTPase. How exactly MFN mediates membrane fusion is poorly understood. Here, we determined crystal structures of a minimal GTPase domain (MGD) of human MFN1, including the predicted GTPase and the distal part of the C-terminal tail (CT). The structures revealed that a helix bundle (HB) formed by three helices extending from the GTPase and one extending from the CT closely attaches to the GTPase domain, resembling the configuration of bacterial dynamin-like protein. We show that the nucleotide-binding pocket is shallow and narrow, rendering weak hydrolysis and less dependence on magnesium ion, and that association of HB affects GTPase activity. MFN1 forms a dimer when GTP or GDP/BeF3−, but not GDP or other analogs, is added. In addition, clustering of vesicles containing membrane-anchored MGD requires continuous GTP hydrolysis. These results suggest that MFN tethers apposing membranes, likely through nucleotide-dependent dimerization.
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Affiliation(s)
- Yuanbo Qi
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China.,Tianjin Key Laboratory of Protein Sciences, Nankai University, Tianjin 300071, China
| | - Liming Yan
- School of Medicine, Tsinghua University, Beijing 100084, China
| | - Caiting Yu
- School of Medicine, Tsinghua University, Beijing 100084, China
| | - Xiangyang Guo
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China.,Tianjin Key Laboratory of Protein Sciences, Nankai University, Tianjin 300071, China
| | - Xin Zhou
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China.,Tianjin Key Laboratory of Protein Sciences, Nankai University, Tianjin 300071, China
| | - Xiaoyu Hu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China.,Tianjin Key Laboratory of Protein Sciences, Nankai University, Tianjin 300071, China
| | - Xiaofang Huang
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China.,Tianjin Key Laboratory of Protein Sciences, Nankai University, Tianjin 300071, China
| | - Zihe Rao
- School of Medicine, Tsinghua University, Beijing 100084, China .,National Laboratory of Macromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing 100101, China
| | - Zhiyong Lou
- School of Medicine, Tsinghua University, Beijing 100084, China
| | - Junjie Hu
- National Laboratory of Macromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing 100101, China
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38
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Wang X, Li S, Wang H, Shui W, Hu J. Quantitative proteomics reveal proteins enriched in tubular endoplasmic reticulum of Saccharomyces cerevisiae. eLife 2017; 6. [PMID: 28287394 PMCID: PMC5358975 DOI: 10.7554/elife.23816] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Accepted: 03/06/2017] [Indexed: 01/04/2023] Open
Abstract
The tubular network is a critical part of the endoplasmic reticulum (ER). The network is shaped by the reticulons and REEPs/Yop1p that generate tubules by inducing high membrane curvature, and the dynamin-like GTPases atlastin and Sey1p/RHD3 that connect tubules via membrane fusion. However, the specific functions of this ER domain are not clear. Here, we isolated tubule-based microsomes from Saccharomyces cerevisiae via classical cell fractionation and detergent-free immunoprecipitation of Flag-tagged Yop1p, which specifically localizes to ER tubules. In quantitative comparisons of tubule-derived and total microsomes, we identified a total of 79 proteins that were enriched in the ER tubules, including known proteins that organize the tubular ER network. Functional categorization of the list of proteins revealed that the tubular ER network may be involved in membrane trafficking, lipid metabolism, organelle contact, and stress sensing. We propose that affinity isolation coupled with quantitative proteomics is a useful tool for investigating ER functions. DOI:http://dx.doi.org/10.7554/eLife.23816.001
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Affiliation(s)
- Xinbo Wang
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, China
| | - Shanshan Li
- iHuman Institute and School of Life Science and Technology, ShanghaiTech University, Shanghai, China
| | - Haicheng Wang
- College of Life Sciences, Huazhong University of Science and Technology, Wuhan, China
| | - Wenqing Shui
- iHuman Institute and School of Life Science and Technology, ShanghaiTech University, Shanghai, China
| | - Junjie Hu
- National Laboratory of Biomacromolecules and CAS Center for Excellence in Biomacromolecules, Institue of Biophysics, Chinese Academy of Sciences, Beijing, China
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39
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Reconstitution of the tubular endoplasmic reticulum network with purified components. Nature 2017; 543:257-260. [PMID: 28225760 PMCID: PMC5853125 DOI: 10.1038/nature21387] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 01/10/2017] [Indexed: 12/22/2022]
Abstract
Organelles display characteristic morphologies that are intimately tied to their cellular function, but how organelles are shaped is poorly understood. The endoplasmic reticulum (ER) is particularly intriguing, as it is comprised of morphologically distinct domains, including a dynamic network of interconnected membrane tubules. Several membrane proteins have been implicated in network formation1–5, but how exactly they mediate network formation and whether they are all required is unclear. Here, we have reconstituted a dynamic tubular membrane network with purified ER proteins. Proteoliposomes containing the membrane-fusing GTPase Sey1p6,7 and the curvature-stabilizing protein Yop1p8,9 from Saccharomyces cerevisiae form a tubular network upon GTP addition. The tubules rapidly fragment when GTP hydrolysis of Sey1p is inhibited, indicating that network maintenance requires continuous membrane fusion and that Yop1p favors the generation of highly curved membrane structures. Sey1p also forms networks with other curvature-stabilizing proteins, including reticulon8 and REEP10 proteins from different species. Atlastin, the vertebrate ortholog of Sey1p6,11, forms a GTP-hydrolysis dependent network on its own, serving as both a fusion and curvature-stabilizing protein. Our results show that organelle shape can be generated by a surprisingly small set of proteins and represents an energy-dependent steady state between formation and disassembly.
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40
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Wang S, Tukachinsky H, Romano FB, Rapoport TA. Cooperation of the ER-shaping proteins atlastin, lunapark, and reticulons to generate a tubular membrane network. eLife 2016; 5. [PMID: 27619977 PMCID: PMC5021524 DOI: 10.7554/elife.18605] [Citation(s) in RCA: 121] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 07/28/2016] [Indexed: 12/29/2022] Open
Abstract
In higher eukaryotes, the endoplasmic reticulum (ER) contains a network of membrane tubules, which transitions into sheets during mitosis. Network formation involves curvature-stabilizing proteins, including the reticulons (Rtns), as well as the membrane-fusing GTPase atlastin (ATL) and the lunapark protein (Lnp). Here, we have analyzed how these proteins cooperate. ATL is needed to not only form, but also maintain, the ER network. Maintenance requires a balance between ATL and Rtn, as too little ATL activity or too high Rtn4a concentrations cause ER fragmentation. Lnp only affects the abundance of three-way junctions and tubules. We suggest a model in which ATL-mediated fusion counteracts the instability of free tubule ends. ATL tethers and fuses tubules stabilized by the Rtns, and transiently sits in newly formed three-way junctions. Lnp subsequently moves into the junctional sheets and forms oligomers. Lnp is inactivated by mitotic phosphorylation, which contributes to the tubule-to-sheet conversion of the ER.
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Affiliation(s)
- Songyu Wang
- Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Hanna Tukachinsky
- Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Fabian B Romano
- Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Tom A Rapoport
- Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.,Department of Cell Biology, Harvard Medical School, Boston, United States
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41
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Daumke O, Praefcke GJK. Invited review: Mechanisms of GTP hydrolysis and conformational transitions in the dynamin superfamily. Biopolymers 2016; 105:580-93. [PMID: 27062152 PMCID: PMC5084822 DOI: 10.1002/bip.22855] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Revised: 03/31/2016] [Accepted: 04/01/2016] [Indexed: 12/29/2022]
Abstract
Dynamin superfamily proteins are multidomain mechano-chemical GTPases which are implicated in nucleotide-dependent membrane remodeling events. A prominent feature of these proteins is their assembly- stimulated mechanism of GTP hydrolysis. The molecular basis for this reaction has been initially clarified for the dynamin-related guanylate binding protein 1 (GBP1) and involves the transient dimerization of the GTPase domains in a parallel head-to-head fashion. A catalytic arginine finger from the phosphate binding (P-) loop is repositioned toward the nucleotide of the same molecule to stabilize the transition state of GTP hydrolysis. Dynamin uses a related dimerization-dependent mechanism, but instead of the catalytic arginine, a monovalent cation is involved in catalysis. Still another variation of the GTP hydrolysis mechanism has been revealed for the dynamin-like Irga6 which bears a glycine at the corresponding position in the P-loop. Here, we highlight conserved and divergent features of GTP hydrolysis in dynamin superfamily proteins and show how nucleotide binding and hydrolysis are converted into mechano-chemical movements. We also describe models how the energy of GTP hydrolysis can be harnessed for diverse membrane remodeling events, such as membrane fission or fusion. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 580-593, 2016.
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Affiliation(s)
- Oliver Daumke
- Kristallographie, Max-Delbrück Centrum Für Molekulare Medizin, Robert-Rössle-Straße 10, Berlin, 13125, Germany
- Institut Für Chemie und Biochemie, Freie Universität Berlin, Takustraße 3, Berlin, 14195, Germany
| | - Gerrit J K Praefcke
- Abteilung Hämatologie/Transfusionsmedizin, Paul-Ehrlich-Institut, Paul-Ehrlich-Straße 51-59, Langen, 63225, Germany
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Zhang H, Hu J. Shaping the Endoplasmic Reticulum into a Social Network. Trends Cell Biol 2016; 26:934-943. [PMID: 27339937 DOI: 10.1016/j.tcb.2016.06.002] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Revised: 05/25/2016] [Accepted: 06/02/2016] [Indexed: 10/21/2022]
Abstract
In eukaryotic cells, the endoplasmic reticulum (ER) is constructed as a network of tubules and sheets that exist in one continuous membrane system. Several classes of integral membrane protein have been shown to shape ER membranes. Functional studies using mutant proteins have begun to reveal the significance of ER morphology and membrane dynamics. In this review, we discuss the common protein modules and mechanisms that generate the characteristic shape of the ER. We also describe the cellular functions closely related to ER morphology, particularly contacts with other membrane systems, and their potential roles in the development of multicellular organisms.
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Affiliation(s)
- Hong Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
| | - Junjie Hu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
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Fusion of the endoplasmic reticulum by membrane-bound GTPases. Semin Cell Dev Biol 2016; 60:105-111. [PMID: 27269373 DOI: 10.1016/j.semcdb.2016.06.001] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 05/31/2016] [Accepted: 06/02/2016] [Indexed: 12/14/2022]
Abstract
The endoplasmic reticulum (ER) membrane forms an elaborate network of tubules and sheets that is continuously remodeled. This dynamic behavior requires membrane fusion that is mediated by dynamin-like GTPases: the atlastins in metazoans and Sey1p and related proteins in yeast and plants. Crystal structures of the cytosolic domains of these membrane proteins and biochemical experiments can now be integrated into a model that explains many aspects of the molecular mechanism by which these membrane-bound GTPases mediate membrane fusion.
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Sugiura S, Mima J. Physiological lipid composition is vital for homotypic ER membrane fusion mediated by the dynamin-related GTPase Sey1p. Sci Rep 2016; 6:20407. [PMID: 26838333 PMCID: PMC4738300 DOI: 10.1038/srep20407] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 01/06/2016] [Indexed: 11/09/2022] Open
Abstract
Homotypic fusion of the endoplasmic reticulum (ER) is required for generating and maintaining the characteristic reticular ER membrane structures. This organelle membrane fusion process depends on the ER-bound dynamin-related GTPases, such as atlastins in animals and Sey1p in yeast. Here, to investigate whether specific lipid molecules facilitate GTPase-dependent ER membrane fusion directly, we comprehensively evaluated membrane docking and lipid mixing of reconstituted proteoliposomes bearing purified Sey1p and a set of ER-mimicking lipids, including phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidic acid, and ergosterol. Remarkably, we revealed that each specific lipid species contributed little to membrane docking mediated by Sey1p. Nevertheless, Sey1p-dependent lipid mixing was strongly reduced by omitting three major acidic lipids from the ER-mimicking set and, moreover, was entirely abolished by omitting either phosphatidylethanolamine or ergosterol. Our reconstitution studies thus established that physiological lipid composition is vital for lipid bilayer rearrangements in GTPase-mediated homotypic ER membrane fusion.
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Affiliation(s)
- Shintaro Sugiura
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - Joji Mima
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
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