1
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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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2
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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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3
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Lipowsky R, Pramanik S, Benk AS, Tarnawski M, Spatz JP, Dimova R. Elucidating the Morphology of the Endoplasmic Reticulum: Puzzles and Perspectives. ACS NANO 2023. [PMID: 37377213 DOI: 10.1021/acsnano.3c01338] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/29/2023]
Abstract
Artificial or synthetic organelles are a key challenge for bottom-up synthetic biology. So far, synthetic organelles have typically been based on spherical membrane compartments, used to spatially confine selected chemical reactions. In vivo, these compartments are often far from being spherical and can exhibit rather complex architectures. A particularly fascinating example is provided by the endoplasmic reticulum (ER), which extends throughout the whole cell by forming a continuous network of membrane nanotubes connected by three-way junctions. The nanotubes have a typical diameter of between 50 and 100 nm. In spite of much experimental progress, several fundamental aspects of the ER morphology remain elusive. A long-standing puzzle is the straight appearance of the tubules in the light microscope, which form irregular polygons with contact angles close to 120°. Another puzzling aspect is the nanoscopic shapes of the tubules and junctions, for which very different images have been obtained by electron microcopy and structured illumination microscopy. Furthermore, both the formation and maintenance of the reticular networks require GTP and GTP-hydrolyzing membrane proteins. In fact, the networks are destroyed by the fragmentation of nanotubes when the supply of GTP is interrupted. Here, it is argued that all of these puzzling observations are intimately related to each other and to the dimerization of two membrane proteins anchored to the same membrane. So far, the functional significance of this dimerization process remained elusive and, thus, seemed to waste a lot of GTP. However, this process can generate an effective membrane tension that stabilizes the irregular polygonal geometry of the reticular networks and prevents the fragmentation of their tubules, thereby maintaining the integrity of the ER. By incorporating the GTP-hydrolyzing membrane proteins into giant unilamellar vesicles, the effective membrane tension will become accessible to systematic experimental studies.
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Affiliation(s)
- Reinhard Lipowsky
- Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
| | - Shreya Pramanik
- Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
| | - Amelie S Benk
- Max Planck Institute for Medical Research, 69120 Heidelberg, Germany
| | | | - Joachim P Spatz
- Max Planck Institute for Medical Research, 69120 Heidelberg, Germany
| | - Rumiana Dimova
- Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany
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4
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Jang E, Moon Y, Yoon SY, Diaz JAR, Lee M, Ko N, Park J, Eom SH, Lee C, Jun Y. Human atlastins are sufficient to drive the fusion of liposomes with a physiological lipid composition. J Cell Biol 2023; 222:e202109090. [PMID: 36757370 PMCID: PMC9949273 DOI: 10.1083/jcb.202109090] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 10/20/2022] [Accepted: 01/17/2023] [Indexed: 02/10/2023] Open
Abstract
The dynamin-like GTPase atlastin is believed to be the minimal machinery required for homotypic endoplasmic reticulum (ER) membrane fusion, mainly because Drosophila atlastin is sufficient to drive liposome fusion. However, it remains unclear whether mammalian atlastins, including the three human atlastins, are sufficient to induce liposome fusion, raising doubts about their major roles in mammalian cells. Here, we show that all human atlastins are sufficient to induce fusion when reconstituted into liposomes with a lipid composition mimicking that of the ER. Although the fusogenic activity of ATL1, which is predominantly expressed in neuronal cells, was weaker than that of ATL2 or ATL3, the addition of M1-spastin, a neuron-specific factor, markedly increased ATL1-mediated liposome fusion. Although we observed efficient fusion between ER microsomes isolated from cultured, non-neuronal cells that predominantly express ATL2-1, an autoinhibited isoform of ATL2, ATL2-1 failed to support liposome fusion by itself as reported previously, indicating that cellular factors enable ATL2-1 to mediate ER fusion in vivo.
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Affiliation(s)
- Eunhong Jang
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Yeojin Moon
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - So Young Yoon
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Joyce Anne R. Diaz
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Miriam Lee
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Naho Ko
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Jongseo Park
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Soo Hyun Eom
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Changwook Lee
- Department of Biological Sciences, School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
| | - Youngsoo Jun
- School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
- Cell Logistics Research Center, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea
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5
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Crosby D, Mikolaj MR, Nyenhuis SB, Bryce S, Hinshaw JE, Lee TH. Reconstitution of human atlastin fusion activity reveals autoinhibition by the C terminus. J Cell Biol 2022; 221:212879. [PMID: 34817557 PMCID: PMC8624677 DOI: 10.1083/jcb.202107070] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 10/13/2021] [Accepted: 11/12/2021] [Indexed: 01/31/2023] Open
Abstract
ER network formation depends on membrane fusion by the atlastin (ATL) GTPase. In humans, three paralogs are differentially expressed with divergent N- and C-terminal extensions, but their respective roles remain unknown. This is partly because, unlike Drosophila ATL, the fusion activity of human ATLs has not been reconstituted. Here, we report successful reconstitution of fusion activity by the human ATLs. Unexpectedly, the major splice isoforms of ATL1 and ATL2 are each autoinhibited, albeit to differing degrees. For the more strongly inhibited ATL2, autoinhibition mapped to a C-terminal α-helix is predicted to be continuous with an amphipathic helix required for fusion. Charge reversal of residues in the inhibitory domain strongly activated its fusion activity, and overexpression of this disinhibited version caused ER collapse. Neurons express an ATL2 splice isoform whose sequence differs in the inhibitory domain, and this form showed full fusion activity. These findings reveal autoinhibition and alternate splicing as regulators of atlastin-mediated ER fusion.
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Affiliation(s)
- Daniel Crosby
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
| | - Melissa R Mikolaj
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - Sarah B Nyenhuis
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - Samantha Bryce
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
| | - Jenny E Hinshaw
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - Tina H Lee
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA
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6
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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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7
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Kelly CM, Byrnes LJ, Neela N, Sondermann H, O'Donnell JP. The hypervariable region of atlastin-1 is a site for intrinsic and extrinsic regulation. J Cell Biol 2021; 220:212648. [PMID: 34546351 PMCID: PMC8563291 DOI: 10.1083/jcb.202104128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Revised: 08/03/2021] [Accepted: 09/02/2021] [Indexed: 11/30/2022] Open
Abstract
Atlastin (ATL) GTPases catalyze homotypic membrane fusion of the peripheral endoplasmic reticulum (ER). GTP-hydrolysis–driven conformational changes and membrane tethering are prerequisites for proper membrane fusion. However, the molecular basis for regulation of these processes is poorly understood. Here we establish intrinsic and extrinsic modes of ATL1 regulation that involve the N-terminal hypervariable region (HVR) of ATLs. Crystal structures of ATL1 and ATL3 exhibit the HVR as a distinct, isoform-specific structural feature. Characterizing the functional role of ATL1’s HVR uncovered its positive effect on membrane tethering and on ATL1’s cellular function. The HVR is post-translationally regulated through phosphorylation-dependent modification. A kinase screen identified candidates that modify the HVR site specifically, corresponding to the modifications on ATL1 detected in cells. This work reveals how the HVR contributes to efficient and potentially regulated activity of ATLs, laying the foundation for the identification of cellular effectors of ATL-mediated membrane processes.
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Affiliation(s)
- Carolyn M Kelly
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY
| | - Laura J Byrnes
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY
| | - Niharika Neela
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY
| | - Holger Sondermann
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY.,CSSB Centre for Structural Systems Biology, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.,Kiel University, Kiel, Germany
| | - John P O'Donnell
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY.,Cell Biology Division, Medical Research Counsil (MRC) Laboratory of Molecular Biology, Cambridge, UK
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8
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Montagna A, Vajente N, Pendin D, Daga A. In vivo Analysis of CRISPR/Cas9 Induced Atlastin Pathological Mutations in Drosophila. Front Neurosci 2020; 14:547746. [PMID: 33177972 PMCID: PMC7593789 DOI: 10.3389/fnins.2020.547746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 09/09/2020] [Indexed: 11/13/2022] Open
Abstract
The endoplasmic reticulum (ER) is a highly dynamic network whose shape is thought to be actively regulated by membrane resident proteins. Mutation of several such morphology regulators cause the neurological disorder Hereditary Sp astic Paraplegia (HSP), suggesting a critical role of ER shape maintenance in neuronal activity and function. Human Atlastin-1 mutations are responsible for SPG3A, the earliest onset and one of the more severe forms of dominant HSP. Atlastin has been initially identified in Drosophila as the GTPase responsible for the homotypic fusion of ER membrane. The majority of SPG3A-linked Atlastin-1 mutations map to the GTPase domain, potentially interfering with atlastin GTPase activity, and to the three-helix-bundle (3HB) domain, a region critical for homo-oligomerization. Here we have examined the in vivo effects of four pathogenetic missense mutations (two mapping to the GTPase domain and two to the 3HB domain) using two complementary approaches: CRISPR/Cas9 editing to introduce such variants in the endogenous atlastin gene and transgenesis to generate lines overexpressing atlastin carrying the same pathogenic variants. We found that all pathological mutations examined reduce atlastin activity in vivo although to different degrees of severity. Moreover, overexpression of the pathogenic variants in a wild type atlastin background does not give rise to the loss of function phenotypes expected for dominant negative mutations. These results indicate that the four pathological mutations investigated act through a loss of function mechanism.
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Affiliation(s)
- Aldo Montagna
- Laboratory of Molecular Biology, Scientific Institute IRCCS E. Medea, Lecco, Italy
| | - Nicola Vajente
- Neuroscience Institute, Italian National Research Council, Padua, Italy.,Department of Biomedical Sciences, University of Padua, Padua, Italy
| | - Diana Pendin
- Neuroscience Institute, Italian National Research Council, Padua, Italy.,Department of Biomedical Sciences, University of Padua, Padua, Italy
| | - Andrea Daga
- Laboratory of Molecular Biology, Scientific Institute IRCCS E. Medea, Lecco, Italy
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9
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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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10
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Neufeldt CJ, Cortese M, Scaturro P, Cerikan B, Wideman JG, Tabata K, Moraes T, Oleksiuk O, Pichlmair A, Bartenschlager R. ER-shaping atlastin proteins act as central hubs to promote flavivirus replication and virion assembly. Nat Microbiol 2019; 4:2416-2429. [PMID: 31636417 PMCID: PMC6881184 DOI: 10.1038/s41564-019-0586-3] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Accepted: 09/10/2019] [Indexed: 12/13/2022]
Abstract
Flaviviruses, including dengue virus (DV) and Zika virus, extensively remodel the cellular endomembrane network to generate replication organelles that promote viral genome replication and virus production. However, it remains unclear how these membranes and associated cellular proteins act during the virus cycle. Here, we show that atlastins (ATLs), a subset of ER resident proteins involved in neurodegenerative diseases, have dichotomous effects on flaviviruses with ATL2 depletion leading to replication organelle defects and ATL3 depletion to changes in virus production pathways. We characterized non-conserved functional domains in ATL paralogues and show that the ATL interactome is profoundly reprogrammed upon DV infection. Screen analysis confirmed non-redundant ATL functions and identified a specific role for ATL3, and its interactor ARF4, in vesicle trafficking and virion maturation. Our data identify ATLs as central hubs targeted by flaviviruses to establish their replication organelle and to achieve efficient virion maturation and secretion.
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Affiliation(s)
- Christopher J Neufeldt
- Department of Infectious Diseases, Molecular Virology, Heidelberg University, Heidelberg, Germany.
| | - Mirko Cortese
- Department of Infectious Diseases, Molecular Virology, Heidelberg University, Heidelberg, Germany
| | - Pietro Scaturro
- Technical University of Munich, School of Medicine, Institute of Virology, Munich, Germany
| | - Berati Cerikan
- Department of Infectious Diseases, Molecular Virology, Heidelberg University, Heidelberg, Germany
| | - Jeremy G Wideman
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.,Biodesign Center for Mechanisms of Evolution, School of Life Sciences, Arizona State University, Tempe, AZ, USA
| | - Keisuke Tabata
- Department of Infectious Diseases, Molecular Virology, Heidelberg University, Heidelberg, Germany
| | - Thaís Moraes
- Department of Infectious Diseases, Molecular Virology, Heidelberg University, Heidelberg, Germany
| | - Olga Oleksiuk
- Department of Infectious Diseases, Molecular Virology, Heidelberg University, Heidelberg, Germany
| | - Andreas Pichlmair
- Technical University of Munich, School of Medicine, Institute of Virology, Munich, Germany.,German Center for Infection Research (DZIF), (Munich Partner Site), Munich, Germany
| | - Ralf Bartenschlager
- Department of Infectious Diseases, Molecular Virology, Heidelberg University, Heidelberg, Germany. .,German Center for Infection Research (DZIF), (Heidelberg Partner Site), Heidelberg, Germany. .,Division Virus-Associated Carcinogenesis, German Cancer Research Center, Heidelberg, Germany.
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11
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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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12
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Krols M, Asselbergh B, De Rycke R, De Winter V, Seyer A, Müller FJ, Kurth I, Bultynck G, Timmerman V, Janssens S. Sensory neuropathy-causing mutations in ATL3 affect ER-mitochondria contact sites and impair axonal mitochondrial distribution. Hum Mol Genet 2019; 28:615-627. [PMID: 30339187 PMCID: PMC6360276 DOI: 10.1093/hmg/ddy352] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Revised: 08/22/2018] [Accepted: 09/28/2018] [Indexed: 11/25/2022] Open
Abstract
Axonopathies are neurodegenerative disorders caused by axonal degeneration, affecting predominantly the longest neurons. Several of these axonopathies are caused by genetic defects in proteins involved in the shaping and dynamics of the endoplasmic reticulum (ER); however, it is unclear how these defects impinge on neuronal survival. Given its central and widespread position within a cell, the ER is a pivotal player in inter-organelle communication. Here, we demonstrate that defects in the ER fusion protein ATL3, which were identified in patients suffering from hereditary sensory and autonomic neuropathy, result in an increased number of ER-mitochondria contact sites both in HeLa cells and in patient-derived fibroblasts. This increased contact is reflected in higher phospholipid metabolism, upregulated autophagy and augmented Ca2+ crosstalk between both organelles. Moreover, the mitochondria in these cells display lowered motility, and the number of axonal mitochondria in neurons expressing disease-causing mutations in ATL3 is strongly decreased. These results underscore the functional interdependence of subcellular organelles in health and disease and show that disorders caused by ER-shaping defects are more complex than previously assumed.
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Affiliation(s)
- Michiel Krols
- Peripheral Neuropathy Research Group, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- Institute Born Bunge, Antwerp, Belgium
| | - Bob Asselbergh
- VIB Center for Molecular Neurology, University of Antwerp, Antwerpen, Belgium
| | - Riet De Rycke
- VIB BioImaging Core, VIB, Ghent, Belgium
- Department of Biomedical Molecular Biology, Ghent University, Ghent, Belgium
- VIB Center for Inflammation Research, Ghent, Belgium
| | - Vicky De Winter
- Peripheral Neuropathy Research Group, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- Institute Born Bunge, Antwerp, Belgium
| | - Alexandre Seyer
- Profilomic SA, Boulogne-Billancourt, and MedDay Pharmaceuticals, Paris, France
| | - Franz-Josef Müller
- Zentrum für Integrative Psychiatrie, University Hospital Schleswig-Holstein, Kiel, Germany
- Max-Planck Institute for Molecular Genetics, Berlin, Germany
| | - Ingo Kurth
- Institute of Human Genetics, Medical Faculty, RWTH Aachen University, Aachen, Germany
| | - Geert Bultynck
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium
| | - Vincent Timmerman
- Peripheral Neuropathy Research Group, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- Institute Born Bunge, Antwerp, Belgium
| | - Sophie Janssens
- Laboratory of ER Stress and Inflammation, VIB Center for Inflammation Research, Ghent, Belgium
- Department of Internal Medicine, Ghent University, Ghent, Belgium
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13
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Chen Q, Xiao Y, Chai P, Zheng P, Teng J, Chen J. ATL3 Is a Tubular ER-Phagy Receptor for GABARAP-Mediated Selective Autophagy. Curr Biol 2019; 29:846-855.e6. [PMID: 30773365 DOI: 10.1016/j.cub.2019.01.041] [Citation(s) in RCA: 196] [Impact Index Per Article: 39.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Revised: 12/06/2018] [Accepted: 01/15/2019] [Indexed: 12/30/2022]
Abstract
The endoplasmic reticulum (ER) consists of the nuclear envelope and both peripheral ER sheets and a peripheral tubular network [1, 2]. In response to physiological or pathological conditions, receptor-mediated selective ER-phagy, engulfing specific ER subdomains or components, is essential for ER turnover and homeostasis [3-6]. Four mammalian receptors for ER-phagy have been reported: FAM134B [7], reticulon 3 (RTN3) [8], SEC62 [9], and CCPG1 [10]. However, these ER-phagy receptors function in subcellular- and tissue- or physiological- and pathological-condition-specific manners, so the diversity of ER-phagy receptors and underlying mechanisms remain largely unknown [3, 4]. Atlastins (ATL1, ATL2, and ATL3), in mammals, are a class of membrane-bound, dynamin-like GTPases that function in ER fusion [11, 12]. ATL1 is expressed mainly in the central nervous system, while ATL2 and ATL3 are more ubiquitously distributed [13]. Recent studies showed that ATL2 mainly affects ER morphology by promoting ER fusion, whereas alterations in ER morphology are hardly detectable after ATL3 depletion [14, 15]. Here, we show that ATL3 functions as a receptor for ER-phagy, promoting tubular ER degradation upon starvation. ATL3 specifically binds to GABARAP, but not LC3, subfamily proteins via 2 GABARAP interaction motifs (GIMs). ATL3-GABARAP interaction is essential for ATL3 to function in ER-phagy. Moreover, hereditary sensory and autonomic neuropathy type I (HSAN I)-associated ATL3 mutations (Y192C and P338R) disrupt ATL3's association with GABARAP and impair ATL3's function in ER-phagy, suggesting that defective ER-phagy is involved in HSAN I. Therefore, we reveal a new ATL3 function for GABARAP-mediated ER-phagy in the degradation of tubular ER.
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Affiliation(s)
- Qingzhou Chen
- Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education, State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, Beijing 100871, China
| | - Ya Xiao
- Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education, State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, Beijing 100871, China
| | - Peiyuan Chai
- Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education, State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, Beijing 100871, China
| | - Pengli Zheng
- Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education, State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, Beijing 100871, China
| | - Junlin Teng
- Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education, State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, Beijing 100871, China.
| | - Jianguo Chen
- Key Laboratory of Cell Proliferation and Differentiation of the Ministry of Education, State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, Beijing 100871, China; Center for Quantitative Biology, Peking University, Beijing 100871, China.
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14
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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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15
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Betancourt-Solis MA, Desai T, McNew JA. The atlastin membrane anchor forms an intramembrane hairpin that does not span the phospholipid bilayer. J Biol Chem 2018; 293:18514-18524. [PMID: 30287684 DOI: 10.1074/jbc.ra118.003812] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 09/27/2018] [Indexed: 12/27/2022] Open
Abstract
The endoplasmic reticulum (ER) is composed of flattened sheets and interconnected tubules that extend throughout the cytosol and makes physical contact with all other cytoplasmic organelles. This cytoplasmic distribution requires continuous remodeling. These discrete ER morphologies require specialized proteins that drive and maintain membrane curvature. The GTPase atlastin is required for homotypic fusion of ER tubules. All atlastin homologs possess a conserved domain architecture consisting of a GTPase domain, a three-helix bundle middle domain, a hydrophobic membrane anchor, and a C-terminal cytosolic tail. Here, we examined several Drosophila-human atlastin chimeras to identify functional domains of human atlastin-1 in vitro Although all chimeras could hydrolyze GTP, only chimeras containing the human C-terminal tail, hydrophobic segments, or both could fuse membranes in vitro We also determined that co-reconstitution of atlastin with reticulon does not influence GTPase activity or membrane fusion. Finally, we found that both human and Drosophila atlastin hydrophobic membrane anchors do not span the membrane, but rather form two intramembrane hairpin loops. The topology of these hairpins remains static during membrane fusion and does not appear to play an active role in lipid mixing.
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Affiliation(s)
| | - Tanvi Desai
- From the Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005
| | - James A McNew
- From the Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005
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16
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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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17
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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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18
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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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19
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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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20
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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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21
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Liu TH, Dong XL, Pan CX, Du GY, Wu YF, Yang JG, Chen P, Lu C, Pan MH. A newly discovered member of the Atlastin family, BmAtlastin-n, has an antiviral effect against BmNPV in Bombyx mori. Sci Rep 2016; 6:28946. [PMID: 27353084 PMCID: PMC4926086 DOI: 10.1038/srep28946] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 06/06/2016] [Indexed: 11/09/2022] Open
Abstract
Atlastin is a member of the dynamin protein superfamily and it can mediate homotypic fusion of endoplasmic reticulum (ER) membranes, which is required for many biological processes. In this study, a new Atlastin homologous protein, BmAtlastin-n, was characterized in silkworms and was found to contain an N-terminal conserved GTPase domain and a coiled-coil middle domain. BmAtlastin-n is localized in the cytoplasm and enriched in silkworm midgut. Results also showed that overexpression of BmAtlastin-n in BmN-SWU1 cells could enhance resistance to BmNPV. To better confirm its antiviral effect, microRNA was used to knock down the expression of BmAtlastin-n in BmE-SWU1 cells with inducing the reproduction of BmNPV. A transgenic expression vector of BmAtlastin-n was constructed and introduced to silkworm embryos by microinjection. The transgenic silkworm also showed considerable antiviral capacity. In conclusion, these findings demonstrate that BmAtlastin-n plays an important role in BmNPV defense. More importantly, the current study may provide a new clue for Atlastin research.
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Affiliation(s)
- Tai-Hang Liu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Xiao-Long Dong
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Cai-Xia Pan
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Guo-Yu Du
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Yun-Fei Wu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Ji-Gui Yang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Peng Chen
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Cheng Lu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China.,Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
| | - Min-Hui Pan
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China.,Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
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22
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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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23
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Yan L, Sun S, Wang W, Shi J, Hu X, Wang S, Su D, Rao Z, Hu J, Lou Z. Structures of the yeast dynamin-like GTPase Sey1p provide insight into homotypic ER fusion. J Cell Biol 2015; 210:961-72. [PMID: 26370501 PMCID: PMC4576867 DOI: 10.1083/jcb.201502078] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The crystal structures of the N-terminal cytosolic domain of Sey1p shed light on the mechanism of Sey1p-mediated ER membrane fusion. Homotypic membrane fusion of the endoplasmic reticulum is mediated by dynamin-like guanosine triphosphatases (GTPases), which include atlastin (ATL) in metazoans and Sey1p in yeast. In this paper, we determined the crystal structures of the cytosolic domain of Sey1p derived from Candida albicans. The structures reveal a stalk-like, helical bundle domain following the GTPase, which represents a previously unidentified configuration of the dynamin superfamily. This domain is significantly longer than that of ATL and critical for fusion. Sey1p forms a side-by-side dimer in complex with GMP-PNP or GDP/AlF4− but is monomeric with GDP. Surprisingly, Sey1p could mediate fusion without GTP hydrolysis, even though fusion was much more efficient with GTP. Sey1p was able to replace ATL in mammalian cells, and the punctate localization of Sey1p was dependent on its GTPase activity. Despite the common function of fusogenic GTPases, our results reveal unique features of Sey1p.
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Affiliation(s)
- Liming Yan
- School of Medicine, Tsinghua University, Beijing, China 100084
| | - Sha Sun
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University and Tianjin Key Laboratory of Protein Sciences, Tianjin, China 300071
| | - Wei Wang
- School of Medicine, Tsinghua University, Beijing, China 100084 State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, Henan University, Kaifeng, China 475004
| | - Juanming Shi
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University and Tianjin Key Laboratory of Protein Sciences, Tianjin, China 300071
| | - Xiaoyu Hu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University and Tianjin Key Laboratory of Protein Sciences, Tianjin, China 300071
| | - Shiyan Wang
- State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, Henan University, Kaifeng, China 475004
| | - Dan Su
- Collaborative Innovation Center for Biotherapy, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, West China Medical School, Sichuan University, Chengdu, China 610041
| | - Zihe Rao
- School of Medicine, Tsinghua University, Beijing, China 100084 National Laboratory of Macromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing, China 100101 Collaborative Innovation Center for Biotherapy, West China Hospital, West China Medical School, Sichuan University, Chengdu, China 610041
| | - Junjie Hu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University and Tianjin Key Laboratory of Protein Sciences, Tianjin, China 300071 National Laboratory of Macromolecules, Institute of Biophysics, Chinese Academy of Science, Beijing, China 100101
| | - Zhiyong Lou
- School of Medicine, Tsinghua University, Beijing, China 100084 Collaborative Innovation Center for Biotherapy, West China Hospital, West China Medical School, Sichuan University, Chengdu, China 610041
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24
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Hu X, Wu F, Sun S, Yu W, Hu J. Human atlastin GTPases mediate differentiated fusion of endoplasmic reticulum membranes. Protein Cell 2015; 6:307-311. [PMID: 25773277 PMCID: PMC4383757 DOI: 10.1007/s13238-015-0139-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- Xiaoyu Hu
- Tianjin Key Laboratory of Protein Sciences, Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071 China
| | - Fuyun Wu
- Tianjin Key Laboratory of Protein Sciences, Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071 China
| | - Sha Sun
- Tianjin Key Laboratory of Protein Sciences, Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071 China
| | - Wenying Yu
- Tianjin Key Laboratory of Protein Sciences, Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071 China
| | - Junjie Hu
- Tianjin Key Laboratory of Protein Sciences, Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, 300071 China.,National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101 China
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25
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Cis and trans interactions between atlastin molecules during membrane fusion. Proc Natl Acad Sci U S A 2015; 112:E1851-60. [PMID: 25825753 DOI: 10.1073/pnas.1504368112] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Atlastin (ATL), a membrane-anchored GTPase that mediates homotypic fusion of endoplasmic reticulum (ER) membranes, is required for formation of the tubular network of the peripheral ER. How exactly ATL mediates membrane fusion is only poorly understood. Here we show that fusion is preceded by the transient tethering of ATL-containing vesicles caused by the dimerization of ATL molecules in opposing membranes. Tethering requires GTP hydrolysis, not just GTP binding, because the two ATL molecules are pulled together most strongly in the transition state of GTP hydrolysis. Most tethering events are futile, so that multiple rounds of GTP hydrolysis are required for successful fusion. Supported lipid bilayer experiments show that ATL molecules sitting on the same (cis) membrane can also undergo nucleotide-dependent dimerization. These results suggest that GTP hydrolysis is required to dissociate cis dimers, generating a pool of ATL monomers that can dimerize with molecules on a different (trans) membrane. In addition, tethering and fusion require the cooperation of multiple ATL molecules in each membrane. We propose a comprehensive model for ATL-mediated fusion that takes into account futile tethering and competition between cis and trans interactions.
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26
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Ulengin I, Park JJ, Lee TH. ER network formation and membrane fusion by atlastin1/SPG3A disease variants. Mol Biol Cell 2015; 26:1616-28. [PMID: 25761634 PMCID: PMC4436774 DOI: 10.1091/mbc.e14-10-1447] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2014] [Accepted: 03/03/2015] [Indexed: 12/20/2022] Open
Abstract
Atlastin catalyzes GTP-dependent membrane fusion to form the ER network. Mutations in atlastin1 cause the disease hereditary spastic paraplegia (HSP), implying that defects in ER membrane fusion cause HSP. Surprisingly, several disease variants are functional in assays for ER network formation and membrane fusion, warranting rethinking of HSP causation by atlastin1 mutations. At least 38 distinct missense mutations in the neuronal atlastin1/SPG3A GTPase are implicated in an autosomal dominant form of hereditary spastic paraplegia (HSP), a motor-neurological disorder manifested by lower limb weakness and spasticity and length-dependent axonopathy of corticospinal motor neurons. Because the atlastin GTPase is sufficient to catalyze membrane fusion and required to form the ER network, at least in nonneuronal cells, it is logically assumed that defects in ER membrane morphogenesis due to impaired fusion activity are the primary drivers of SPG3A-associated HSP. Here we analyzed a subset of established atlastin1/SPG3A disease variants using cell-based assays for atlastin-mediated ER network formation and biochemical assays for atlastin-catalyzed GTP hydrolysis, dimer formation, and membrane fusion. As anticipated, some variants exhibited clear deficits. Surprisingly however, at least two disease variants, one of which represents that most frequently identified in SPG3A HSP patients, displayed wild-type levels of activity in all assays. The same variants were also capable of co-redistributing ER-localized REEP1, a recently identified function of atlastins that requires its catalytic activity. Taken together, these findings indicate that a deficit in the membrane fusion activity of atlastin1 may be a key contributor, but is not required, for HSP causation.
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Affiliation(s)
- Idil Ulengin
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
| | - John J Park
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Tina H Lee
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213
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