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Vasan R, Rudraraju S, Akamatsu M, Garikipati K, Rangamani P. A mechanical model reveals that non-axisymmetric buckling lowers the energy barrier associated with membrane neck constriction. SOFT MATTER 2020; 16:784-797. [PMID: 31830191 DOI: 10.1039/c9sm01494b] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Membrane neck formation is essential for scission, which, as recent experiments on tubules have demonstrated, can be location dependent. The diversity of biological machinery that can constrict a neck such as dynamin, actin, ESCRTs and BAR proteins, and the range of forces and deflection over which they operate, suggest that the constriction process is functionally mechanical and robust to changes in biological environment. In this study, we used a mechanical model of the lipid bilayer to systematically investigate the influence of location, symmetry constraints, and helical forces on membrane neck constriction. Simulations from our model demonstrated that the energy barriers associated with constriction of a membrane neck are location-dependent. Importantly, if symmetry restrictions are relaxed, then the energy barrier for constriction is dramatically lowered and the membrane buckles at lower values of forcing parameters. Our simulations also show that constriction due to helical proteins further reduces the energy barrier for neck formation when compared to cylindrical proteins. These studies establish that despite different molecular mechanisms of neck formation in cells, the mechanics of constriction naturally leads to a loss of symmetry that can lower the energy barrier to constriction.
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Affiliation(s)
- R Vasan
- Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, CA 92093, USA.
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Lee Y, Yamada H, Pradipta A, Ma JS, Okamoto M, Nagaoka H, Takashima E, Standley DM, Sasai M, Takei K, Yamamoto M. Initial phospholipid-dependent Irgb6 targeting to Toxoplasma gondii vacuoles mediates host defense. Life Sci Alliance 2019; 3:3/1/e201900549. [PMID: 31852733 PMCID: PMC6925386 DOI: 10.26508/lsa.201900549] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 12/02/2019] [Accepted: 12/02/2019] [Indexed: 12/19/2022] Open
Abstract
Toxoplasma gondii is an obligate intracellular protozoan parasite capable of infecting warm-blooded animals by ingestion. The organism enters host cells and resides in the cytoplasm in a membrane-bound parasitophorous vacuole (PV). Inducing an interferon response enables IFN-γ-inducible immunity-related GTPase (IRG protein) to accumulate on the PV and to restrict parasite growth. However, little is known about the mechanisms by which IRG proteins recognize and destroy T. gondii PV. We characterized the role of IRG protein Irgb6 in the cell-autonomous response against T. gondii, which involves vacuole ubiquitination and breakdown. We show that Irgb6 is capable of binding a specific phospholipid on the PV membrane. Furthermore, the absence of Irgb6 causes reduced targeting of other effector IRG proteins to the PV. This suggests that Irgb6 has a role as a pioneer in the process by which multiple IRG proteins access the PV. Irgb6-deficient mice are highly susceptible to infection by a strain of T. gondii avirulent in wild-type mice.
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Affiliation(s)
- Youngae Lee
- Department of Immunoparasitology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.,Laboratory of Immunoparasitology, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Hiroshi Yamada
- Department of Neuroscience, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Ariel Pradipta
- Department of Immunoparasitology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
| | - Ji Su Ma
- Department of Immunoparasitology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.,Laboratory of Immunoparasitology, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Masaaki Okamoto
- Department of Immunoparasitology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
| | - Hikaru Nagaoka
- Division of Malaria Research, Proteo-Science Center, Ehime University, Ehime, Japan
| | - Eizo Takashima
- Division of Malaria Research, Proteo-Science Center, Ehime University, Ehime, Japan
| | - Daron M Standley
- Department of Genome Informatics, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.,Laboratory of Systems Immunology, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Miwa Sasai
- Department of Immunoparasitology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.,Laboratory of Immunoparasitology, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Kohji Takei
- Department of Neuroscience, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Masahiro Yamamoto
- Department of Immunoparasitology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan .,Laboratory of Immunoparasitology, WPI Immunology Frontier Research Center, Osaka University, Osaka, Japan
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Krishnan S, Collett M, Robinson PJ. SH3 Domains Differentially Stimulate Distinct Dynamin I Assembly Modes and G Domain Activity. PLoS One 2015; 10:e0144609. [PMID: 26659814 PMCID: PMC4687643 DOI: 10.1371/journal.pone.0144609] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Accepted: 11/20/2015] [Indexed: 11/19/2022] Open
Abstract
Dynamin I is a highly regulated GTPase enzyme enriched in nerve terminals which mediates vesicle fission during synaptic vesicle endocytosis. One regulatory mechanism involves its interactions with proteins containing Src homology 3 (SH3) domains. At least 30 SH3 domain-containing proteins bind dynamin at its proline-rich domain (PRD). Those that stimulate dynamin activity act by promoting its oligomerisation. We undertook a systematic parallel screening of 13 glutathione-S-transferase (GST)-tagged endocytosis-related SH3 domains on dynamin binding, GTPase activity and oligomerisation. No correlation was found between dynamin binding and their potency to stimulate GTPase activity. There was limited correlation between the extent of their ability to stimulate dynamin activity and the level of oligomerisation, indicating an as yet uncharacterised allosteric coupling of the PRD and G domain. We examined the two variants, dynamin Iab and Ibb, which differ in the alternately splice middle domain α2 helix. They responded differently to the panel of SH3s, with the extent of stimulation between the splice variants varying greatly between the SH3s. This study reveals that SH3 binding can act as a heterotropic allosteric regulator of the G domain via the middle domain α2 helix, suggesting an involvement of this helix in communicating the PRD-mediated allostery. This indicates that SH3 binding both stabilises multiple conformations of the tetrameric building block of dynamin, and promotes assembly of dynamin-SH3 complexes with distinct rates of GTP hydrolysis.
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Affiliation(s)
- Sai Krishnan
- Cell Signalling Unit, Children’s Medical Research Institute, The University of Sydney, Westmead, New South Wales, Australia
| | - Michael Collett
- Cell Signalling Unit, Children’s Medical Research Institute, The University of Sydney, Westmead, New South Wales, Australia
| | - Phillip J. Robinson
- Cell Signalling Unit, Children’s Medical Research Institute, The University of Sydney, Westmead, New South Wales, Australia
- * E-mail:
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Schroeder B, McNiven MA. Importance of endocytic pathways in liver function and disease. Compr Physiol 2015; 4:1403-17. [PMID: 25428849 DOI: 10.1002/cphy.c140001] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Hepatocellular endocytosis is a highly dynamic process responsible for the internalization of a variety of different receptor ligand complexes, trophic factors, lipids, and, unfortunately, many different pathogens. The uptake of these external agents has profound effects on seminal cellular processes including signaling cascades, migration, growth, and proliferation. The hepatocyte, like other well-polarized epithelial cells, possesses a host of different endocytic mechanisms and entry routes to ensure the selective internalization of cargo molecules. These pathways include receptor-mediated endocytosis, lipid raft associated endocytosis, caveolae, or fluid-phase uptake, although there are likely many others. Understanding and defining the regulatory mechanisms underlying these distinct entry routes, sorting and vesicle formation, as well as the postendocytic trafficking pathways is of high importance especially in the liver, as their mis-regulation can contribute to aberrant liver pathology and liver diseases. Further, these processes can be "hijacked" by a variety of different infectious agents and viruses. This review provides an overview of common components of the endocytic and postendocytic trafficking pathways utilized by hepatocytes. It will also discuss in more detail how these general themes apply to liver-specific processes including iron homeostasis, HBV infection, and even hepatic steatosis.
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Affiliation(s)
- Barbara Schroeder
- Department of Biochemistry and Molecular Biology, Center for Basic Research in Digestive Diseases, Mayo Clinic and Foundation, Rochester, Minnesota
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Byers CE, Barylko B, Ross JA, Southworth DR, James NG, Taylor CA, Wang L, Collins KA, Estrada A, Waung M, Tassin TC, Huber KM, Jameson DM, Albanesi JP. Enhancement of dynamin polymerization and GTPase activity by Arc/Arg3.1. Biochim Biophys Acta Gen Subj 2015; 1850:1310-8. [PMID: 25783003 DOI: 10.1016/j.bbagen.2015.03.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Revised: 02/17/2015] [Accepted: 03/09/2015] [Indexed: 01/28/2023]
Abstract
BACKGROUND The Activity-regulated cytoskeleton-associated protein, Arc, is an immediate-early gene product implicated in various forms of synaptic plasticity. Arc promotes endocytosis of AMPA type glutamate receptors and regulates cytoskeletal assembly in neuronal dendrites. Its role in endocytosis may be mediated by its reported interaction with dynamin 2, a 100 kDa GTPase that polymerizes around the necks of budding vesicles and catalyzes membrane scission. METHODS Enzymatic and turbidity assays are used in this study to monitor effects of Arc on dynamin activity and polymerization. Arc oligomerization is measured using a combination of approaches, including size exclusion chromatography, sedimentation analysis, dynamic light scattering, fluorescence correlation spectroscopy, and electron microscopy. RESULTS We present evidence that bacterially-expressed His6-Arc facilitates the polymerization of dynamin 2 and stimulates its GTPase activity under physiologic conditions (37°C and 100mM NaCl). At lower ionic strength Arc also stabilizes pre-formed dynamin 2 polymers against GTP-dependent disassembly, thereby prolonging assembly-dependent GTP hydrolysis catalyzed by dynamin 2. Arc also increases the GTPase activity of dynamin 3, an isoform of implicated in dendrite remodeling, but does not affect the activity of dynamin 1, a neuron-specific isoform involved in synaptic vesicle recycling. We further show in this study that Arc (either His6-tagged or untagged) has a tendency to form large soluble oligomers, which may function as a scaffold for dynamin assembly and activation. CONCLUSIONS AND GENERAL SIGNIFICANCE The ability of Arc to enhance dynamin polymerization and GTPase activation may provide a mechanism to explain Arc-mediated endocytosis of AMPA receptors and the accompanying effects on synaptic plasticity.
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Affiliation(s)
- Christopher E Byers
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Barbara Barylko
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Justin A Ross
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 9681, United States
| | - Daniel R Southworth
- Department of Chemistry and Chemical Biology, University of California, San Francisco, CA 94158, United States
| | - Nicholas G James
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 9681, United States
| | - Clinton A Taylor
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Lei Wang
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Katie A Collins
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Armando Estrada
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Maggie Waung
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Tara C Tassin
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - Kimberly M Huber
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States
| | - David M Jameson
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 9681, United States
| | - Joseph P Albanesi
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, United States.
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Sousa R. Structural mechanisms of chaperone mediated protein disaggregation. Front Mol Biosci 2014; 1:12. [PMID: 25988153 PMCID: PMC4428496 DOI: 10.3389/fmolb.2014.00012] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2014] [Accepted: 08/27/2014] [Indexed: 11/13/2022] Open
Abstract
The ClpB/Hsp104 and Hsp70 classes of molecular chaperones use ATP hydrolysis to dissociate protein aggregates and complexes, and to move proteins through membranes. ClpB/Hsp104 are members of the AAA+ family of proteins which form ring-shaped hexamers. Loops lining the pore in the ring engage substrate proteins as extended polypeptides. Interdomain rotations and conformational changes in these loops coupled to ATP hydrolysis unfold and pull proteins through the pore. This provides a mechanism that progressively disrupts local secondary and tertiary structure in substrates, allowing these chaperones to dissociate stable aggregates such as β-sheet rich prions or coiled coil SNARE complexes. While the ClpB/Hsp104 mechanism appears to embody a true power-stroke in which an ATP powered conformational change in one protein is directly coupled to movement or structural change in another, the mechanism of force generation by Hsp70s is distinct and less well understood. Both active power-stroke and purely passive mechanisms in which Hsp70 captures spontaneous fluctuations in a substrate have been proposed, while a third proposed mechanism-entropic pulling-may be able to generate forces larger than seen in ATP-driven molecular motors without the conformational coupling required for a power-stroke. The disaggregase activity of these chaperones is required for thermotolerance, but unrestrained protein complex/aggregate dissociation is potentially detrimental. Disaggregating chaperones are strongly auto-repressed, and are regulated by co-chaperones which recruit them to protein substrates and activate the disaggregases via mechanisms involving either sequential transfer of substrate from one chaperone to another and/or simultaneous interaction of substrate with multiple chaperones. By effectively subjecting substrates to multiple levels of selection by multiple chaperones, this may insure that these potent disaggregases are only activated in the appropriate context.
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Affiliation(s)
- Rui Sousa
- Department of Biochemistry, University of Texas Health Science Center at San Antonio San Antonio, TX, USA
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Alpadi K, Kulkarni A, Namjoshi S, Srinivasan S, Sippel KH, Ayscough K, Zieger M, Schmidt A, Mayer A, Evangelista M, Quiocho FA, Peters C. Dynamin-SNARE interactions control trans-SNARE formation in intracellular membrane fusion. Nat Commun 2013; 4:1704. [PMID: 23591871 PMCID: PMC3630463 DOI: 10.1038/ncomms2724] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 03/08/2013] [Indexed: 11/09/2022] Open
Abstract
The fundamental processes of membrane fission and fusion determine size and copy numbers of intracellular organelles. While SNARE proteins and tethering complexes mediate intracellular membrane fusion, fission requires the presence of dynamin or dynamin-related proteins. Here we study these reactions in native yeast vacuoles and find that the yeast dynamin homolog Vps1 is not only an essential part of the fission machinery, but also controls membrane fusion by generating an active Qa SNARE- tethering complex pool, which is essential for trans-SNARE formation. Our findings provide new insight into the role of dynamins in membrane fusion by directly acting on SNARE proteins.
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Affiliation(s)
- Kannan Alpadi
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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Clathrin and phosphatidylinositol-4,5-bisphosphate regulate autophagic lysosome reformation. Nat Cell Biol 2012; 14:924-34. [PMID: 22885770 DOI: 10.1038/ncb2557] [Citation(s) in RCA: 225] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Accepted: 07/09/2012] [Indexed: 12/23/2022]
Abstract
Autophagy is a lysosome-based degradation pathway. During autophagy, lysosomes fuse with autophagosomes to form autolysosomes. Following starvation-induced autophagy, nascent lysosomes are formed from autolysosomal membranes through an evolutionarily conserved cellular process, autophagic lysosome reformation (ALR), which is critical for maintaining lysosome homeostasis. Here we report that clathrin and phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P(2)) regulate ALR. Combining a screen of candidates identified through proteomic analysis of purified ALR tubules, and large-scale RNAi knockdown, we unveiled a tightly regulated molecular pathway that controls lysosome homeostasis, in which clathrin and PtdIns(4,5)P(2) are the central components. Our functional study demonstrates the central role of clathrin and its associated proteins in cargo sorting, phospholipid conversion, initiation of autolysosome tubulation, and proto-lysosome budding during ALR. Our data not only uncover a molecular pathway by which lysosome homeostasis is maintained through the ALR process, but also reveal unexpected functions of clathrin and PtdIns(4,5)P(2) in lysosome homeostasis.
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Abstract
The bacterial tubulin homologue FtsZ forms a ring-like structure called the Z ring that drives cytokinesis. We showed previously that FtsZ-YFP-mts, which has a short amphipathic helix (mts) on its C terminus that inserts into the membrane, can assemble contractile Z rings in tubular liposomes without any other protein. Here we study mts-FtsZ-YFP, where the membrane tether is switched to the opposite side of the protofilament. This assembled 'inside-out' Z rings that wrapped around the outside surface of tubular liposomes. The inside-out Z rings were highly dynamic, and generated a constriction force that squeezed the tubular liposomes from outside. This is consistent with models where the constriction force is generated by curved protofilaments bending the membrane. We used this system to test how GTP hydrolysis by FtsZ is involved in Z-ring constriction. Without GTP hydrolysis, Z rings could still assemble and generate an initial constriction. However, the constriction quickly stopped, suggesting that Z rings became rigidly stabilized in the absence of GTP hydrolysis. We propose that remodelling of the Z ring, mediated by GTP hydrolysis and exchange of subunits, is necessary for the continuous constriction.
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Affiliation(s)
- Masaki Osawa
- Department of Cell Biology, 3079, Duke University Medical Center, Durham, NC 27710-3709, USA.
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Pawlowski N, Khaminets A, Hunn JP, Papic N, Schmidt A, Uthaiah RC, Lange R, Vopper G, Martens S, Wolf E, Howard JC. The activation mechanism of Irga6, an interferon-inducible GTPase contributing to mouse resistance against Toxoplasma gondii. BMC Biol 2011; 9:7. [PMID: 21276251 PMCID: PMC3042988 DOI: 10.1186/1741-7007-9-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2010] [Accepted: 01/28/2011] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The interferon-inducible immunity-related GTPases (IRG proteins/p47 GTPases) are a distinctive family of GTPases that function as powerful cell-autonomous resistance factors. The IRG protein, Irga6 (IIGP1), participates in the disruption of the vacuolar membrane surrounding the intracellular parasite, Toxoplasma gondii, through which it communicates with its cellular hosts. Some aspects of the protein's behaviour have suggested a dynamin-like molecular mode of action, in that the energy released by GTP hydrolysis is transduced into mechanical work that results in deformation and ultimately rupture of the vacuolar membrane. RESULTS Irga6 forms GTP-dependent oligomers in vitro and thereby activates hydrolysis of the GTP substrate. In this study we define the catalytic G-domain interface by mutagenesis and present a structural model, of how GTP hydrolysis is activated in Irga6 complexes, based on the substrate-twinning reaction mechanism of the signal recognition particle (SRP) and its receptor (SRα). In conformity with this model, we show that the bound nucleotide is part of the catalytic interface and that the 3'hydroxyl of the GTP ribose bound to each subunit is essential for trans-activation of hydrolysis of the GTP bound to the other subunit. We show that both positive and negative regulatory interactions between IRG proteins occur via the catalytic interface. Furthermore, mutations that disrupt the catalytic interface also prevent Irga6 from accumulating on the parasitophorous vacuole membrane of T. gondii, showing that GTP-dependent Irga6 activation is an essential component of the resistance mechanism. CONCLUSIONS The catalytic interface of Irga6 defined in the present experiments can probably be used as a paradigm for the nucleotide-dependent interactions of all members of the large family of IRG GTPases, both activating and regulatory. Understanding the activation mechanism of Irga6 will help to explain the mechanism by which IRG proteins exercise their resistance function. We find no support from sequence or G-domain structure for the idea that IRG proteins and the SRP GTPases have a common phylogenetic origin. It therefore seems probable, if surprising, that the substrate-assisted catalytic mechanism has been independently evolved in the two protein families.
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Affiliation(s)
- Nikolaus Pawlowski
- Institute for Genetics, Department of Cell Genetics, University of Cologne, Zülpicher Strasse 47a, 50674 Cologne, Germany
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Bürmann F, Ebert N, van Baarle S, Bramkamp M. A bacterial dynamin-like protein mediating nucleotide-independent membrane fusion. Mol Microbiol 2011; 79:1294-304. [PMID: 21205012 DOI: 10.1111/j.1365-2958.2011.07523.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Dynamins are a family of large GTPases that are involved in key cellular processes, where they mediate events of membrane fission and fusion. The dynamin superfamily is not restricted to eukaryotes but might have a bacterial origin, with many species containing an operon of two genes related to mitofusins. However, it is not clear whether bacterial dynamins promote membrane fission or fusion. The dynamin-like protein DynA of Bacillus subtilis is remarkable in that it arose from a gene fusion of two dynamins and contains two separate dynamin-like subunits and GTPase domains. We found that DynA exhibits strictly auto-regulated GTP hydrolysis, and that progress through the GTPase cycle is concerted within DynA oligomers. Furthermore, we show that DynA can tether membranes and mediates nucleotide-independent membrane fusion in vitro. This process merely requires magnesium as a cofactor. Our results provide a set of minimal requirements for membrane fusion by dynamin-like proteins and have mechanistic implications in particular for the fusion of mitochondria.
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Affiliation(s)
- Frank Bürmann
- Institute for Biochemistry, University of Cologne, Zülpicherstr. 47, 50674 Köln, Germany
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