Membrane Fusion

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Hisao Kondo - One of the best experts on this subject based on the ideXlab platform.

  • Mitotic phosphorylation of VCIP135 blocks p97ATPase-mediated Golgi Membrane Fusion.
    Biochemical and biophysical research communications, 2013
    Co-Authors: Go Totsukawa, Ayaka Matsuo, Ayano Kubota, Yuya Taguchi, Hisao Kondo
    Abstract:

    In mammals, the Golgi apparatus is disassembled early mitosis and reassembled at the end of mitosis. For Golgi disassembly, Membrane Fusion needs to be blocked. Golgi biogenesis requires two distinct p97ATPase-mediated Membrane Fusion, the p97/p47 and p97/p37 pathways. We previously reported that p47 phosphorylation on Serine-140 and p37 phosphorylation on Serine-56 and Threonine-59 result in mitotic inhibition of the p97/p47 and the p97/p37 pathways, respectively [11,14]. In this study, we show another mechanism of mitotic inhibition of p97-mediated Golgi Membrane Fusion. We clarified that VCIP135, an essential factor in both p97 Membrane Fusion pathways, is phosphorylated on Threonine-760 and Serine-767 by Cdc2 at mitosis and that this phosphorylated VCIP135 does not bind to p97. An in vitro Golgi reassembly assay revealed that VCIP135(T760E, S767E), which mimics mitotic phosphorylation, caused no cisternal regrowth. Our results indicate that the phosphorylation of VCIP135 on Threonine-760 and Serine-767 inhibits p97-mediated Golgi Membrane Fusion at mitosis.

  • vcip135 deubiquitinase and its binding protein wac in p97atpase mediated Membrane Fusion
    The EMBO Journal, 2011
    Co-Authors: Go Totsukawa, Hisao Kondo, Yayoi Kaneko, Keiji Uchiyama, Hiroyuki Toh, Kaori Tamura
    Abstract:

    Two distinct p97 Membrane Fusion pathways are required for Golgi biogenesis: the p97/p47 and p97/p37 pathways. VCIP135 is necessary for both pathways, while its deubiquitinating activity is required only for the p97/p47 pathway. We have now identified a novel VCIP135-binding protein, WAC. WAC localizes to the Golgi as well as the nucleus. In Golgi Membranes, WAC is involved in a complex containing VCIP135 and p97. WAC directly binds to VCIP135 and increases its deubiquitinating activity. siRNA experiments revealed that WAC is required for Golgi biogenesis. In an in vitro Golgi reformation assay, WAC was necessary only for p97/p47-mediated Golgi reassembly, but not for p97/p37-mediated reassembly. WAC is hence thought to function in p97/p47-mediated Golgi Membrane Fusion by activating the deubiquitinating function of VCIP135. We also showed that the two p97 pathways function in ER Membrane Fusion as well. An in vitro ER reformation assay revealed that both pathways required VCIP135 but not its deubiquitinating activity for their ER Membrane Fusion. This was consistent with the finding that WAC is unnecessary for p97-mediated ER Membrane Fusion.

Yeon-kyun Shin - One of the best experts on this subject based on the ideXlab platform.

  • Two gigs of Munc18 in Membrane Fusion
    Proceedings of the National Academy of Sciences of the United States of America, 2013
    Co-Authors: Yeon-kyun Shin
    Abstract:

    All Membrane Fusion in eukaryotic cells, except mitochondrial and homotypic endoplasmic reticulum Fusion, is critically dependent upon evolutionarily conserved soluble N-ethylmaleimide–sensitive factor attachment protein receptors (SNAREs) and Sec1/Muc18 (SM) proteins (1, 2). Similar to the cases for SNARE proteins, all SM-null mutants, from yeast to rat, exhibit a significant to complete loss of specific Membrane Fusion events (3, 4), suggesting the possibility of a conserved mechanism for the SM protein family. The SNARE proteins, as a central fusogen, have been well documented (5). In stark contrast, the function of SM proteins has been elusive, despite intense investigations. In PNAS, Yu et al. (6) present unique and exciting results that provide insights into the mechanism by which SM–SNARE interactions play out in driving intracellular Membrane Fusion.

  • multiple intermediates in snare induced Membrane Fusion
    Proceedings of the National Academy of Sciences of the United States of America, 2006
    Co-Authors: Taeyoung Yoon, Fan Zhang, Burak Okumus, Yeon-kyun Shin
    Abstract:

    Membrane Fusion in eukaryotic cells is thought to be mediated by a highly conserved family of proteins called SNAREs (soluble N-ethyl maleimide sensitive-factor attachment protein receptors). The vesicle-associated v-SNARE engages with its partner t-SNAREs on the target Membrane to form a coiled coil that bridges two Membranes and facilitates Fusion. As demonstrated by recent findings on the hemiFusion state, identifying intermediates of Membrane Fusion can help unveil the underlying Fusion mechanism. Observation of SNARE-driven Fusion at the single-liposome level has the potential to dissect and characterize Fusion intermediates most directly. Here, we report on the real-time observation of lipid-mixing dynamics in a single Fusion event between a pair of SNARE-reconstituted liposomes. The assay reveals multiple intermediate states characterized by discrete values of FRET between Membrane-bound fluorophores. HemiFusion, flickering of Fusion pores, and kinetic transitions between intermediates, which would be very difficult to detect in ensemble assays, are now identified. The ability to monitor the time course of Fusion events between two proteoliposomes should be useful for addressing many important issues in SNARE-mediated Membrane Fusion.

  • Membrane Fusion Induced by Neuronal SNAREs Transits through HemiFusion
    The Journal of biological chemistry, 2005
    Co-Authors: Fan Zhang, James A. Mcnew, Yeon-kyun Shin
    Abstract:

    Synaptic transmission requires the controlled release of neurotransmitter from synaptic vesicles by Membrane Fusion with the presynaptic plasma Membrane. SNAREs are the core constituents of the protein machinery responsible for synaptic Membrane Fusion. The mechanism by which SNAREs drive Membrane Fusion is thought to involve a hemiFusion intermediate, a condition in which the outer leaflets of two bilayers are combined and the inner leaflets remain intact; however, hemiFusion has been observed only as an end point rather than as an intermediate. Here, we examined the kinetics of Membrane Fusion of liposomes mediated by recombinant neuronal SNAREs using fluorescence assays that monitor both total lipid mixing and inner leaflet mixing. Our results demonstrate that hemiFusion is dominant at the early stage of the Fusion reaction. Over time, hemiFusion transitioned to complete Fusion, showing that hemiFusion is a true intermediate. We also show that hemiFusion intermediates can be trapped, likely as unproductive outcomes, by modulating the surface concentration of the SNARE proteins.

  • Insights into a Structure-Based Mechanism of Viral Membrane Fusion
    Bioscience reports, 2000
    Co-Authors: Danika L. Leduc, Yeon-kyun Shin
    Abstract:

    A number of different viral spike proteins, responsible for Membrane Fusion, show striking similarities in their core structures. The prospect of developing a general structure-based mechanism seems plausible in light of these newly determined structures. Influenza hemagglutinin (HA) is the best-studied Fusion machine, whose action has previously been described by a hypothetical "spring-loaded" model. This model has recently been extended to explain the mechanism of other systems, such as HIV gp120-gp41. However, evidence supporting this idea is insufficient, requiring re-examination of the mechanism of HA-induced Membrane Fusion. Recent experiments with a shortened construct of HA, which is able to induce lipid mixing, have provided evidence for an alternative scenario for HA-induced Membrane Fusion and perhaps that of other viral systems.

David C. Chan - One of the best experts on this subject based on the ideXlab platform.

  • proteolytic cleavage of opa1 stimulates mitochondrial inner Membrane Fusion and couples Fusion to oxidative phosphorylation
    Cell Metabolism, 2014
    Co-Authors: Prashant Mishra, Valerio Carelli, Giovanni Manfredi, David C. Chan
    Abstract:

    Mitochondrial Fusion is essential for maintenance of mitochondrial function. The mitofusin GTPases control mitochondrial outer Membrane Fusion, whereas the dynamin-related GTPase Opa1 mediates inner Membrane Fusion. We show that mitochondrial inner Membrane Fusion is tuned by the level of oxidative phosphorylation (OXPHOS), whereas outer Membrane Fusion is insensitive. Consequently, cells from patients with pathogenic mtDNA mutations show a selective defect in mitochondrial inner Membrane Fusion. In elucidating the molecular mechanism of OXPHOS-stimulated Fusion, we uncover that real-time proteolytic processing of Opa1 stimulates mitochondrial inner Membrane Fusion. OXPHOS-stimulated mitochondrial Fusion operates through Yme1L, which cleaves Opa1 more efficiently under high OXPHOS conditions. Engineered cleavage of Opa1 is sufficient to mediate inner Membrane Fusion, regardless of respiratory state. Proteolytic cleavage therefore stimulates the Membrane Fusion activity of Opa1, and this feature is exploited to dynamically couple mitochondrial Fusion to cellular metabolism.

  • Mitofusins and OPA1 Mediate Sequential Steps in Mitochondrial Membrane Fusion
    Molecular biology of the cell, 2009
    Co-Authors: Zhiyin Song, Mariam Ghochani, J. Michael Mccaffery, Terrence G. Frey, David C. Chan
    Abstract:

    Mitochondrial Fusion requires the coordinated Fusion of the outer and inner Membranes. Three large GTPases—OPA1 and the mitofusins Mfn1 and Mfn2—are essential for the Fusion of mammalian mitochondria. OPA1 is mutated in dominant optic atrophy, a neurodegenerative disease of the optic nerve. In yeast, the OPA1 ortholog Mgm1 is required for inner Membrane Fusion in vitro; nevertheless, yeast lacking Mgm1 show neither outer nor inner Membrane Fusion in vivo, because of the tight coupling between these two processes. We find that outer Membrane Fusion can be readily visualized in OPA1-null mouse cells in vivo, but these events do not progress to inner Membrane Fusion. Similar defects are found in cells lacking prohibitins, which are required for proper OPA1 processing. In contrast, double Mfn-null cells show neither outer nor inner Membrane Fusion. Mitochondria in OPA1-null cells often contain multiple matrix compartments bounded together by a single outer Membrane, consistent with uncoupling of outer versus inner Membrane Fusion. In addition, unlike mitofusins and yeast Mgm1, OPA1 is not required on adjacent mitochondria to mediate Membrane Fusion. These results indicate that mammalian mitofusins and OPA1 mediate distinct sequential Fusion steps that are readily uncoupled, in contrast to the situation in yeast.

Leonid V. Chernomordik - One of the best experts on this subject based on the ideXlab platform.

  • Membrane tension and Membrane Fusion
    Current opinion in structural biology, 2015
    Co-Authors: Michael M. Kozlov, Leonid V. Chernomordik
    Abstract:

    Diverse cell biological processes that involve shaping and remodeling of cell Membranes are regulated by Membrane lateral tension. Here we focus on the role of tension in driving Membrane Fusion. We discuss the physics of Membrane tension, forces that can generate the tension in plasma Membrane of a cell, and the hypothesis that tension powers expansion of Membrane Fusion pores in late stages of cell-to-cell and exocytotic Fusion. We propose that Fusion pore expansion can require unusually large Membrane tensions or, alternatively, low line tensions of the pore resulting from accumulation in the pore rim of Membrane-bending proteins. Increase of the inter-Membrane distance facilitates the reaction.

  • Mechanics of Membrane Fusion
    Nature Structural & Molecular Biology, 2008
    Co-Authors: Leonid V. Chernomordik, Michael M. Kozlov
    Abstract:

    Diverse Membrane Fusion reactions in biology involve close contact between two lipid bilayers, followed by the local distortion of the individual bilayers and reformation into a single, merged Membrane. We consider the structures and energies of the Fusion intermediates identified in experimental and theoretical work on protein-free lipid bilayers. On the basis of this analysis, we then discuss the conserved Fusion-through-hemiFusion pathway of merger between biological Membranes and propose that the entire progression, from the close juxtaposition of Membrane bilayers to the expansion of a Fusion pore, is controlled by protein-generated Membrane stresses.

  • Lipids in biological Membrane Fusion.
    The Journal of membrane biology, 1995
    Co-Authors: Leonid V. Chernomordik, Michael M. Kozlov, Joshua Zimmerberg
    Abstract:

    The results reviewed suggest that Membrane Fusion in diverse biological Fusion reactions involves formation of some specific intermediates: stalks and pores. Energy of these intermediates and, consequently, the rate and extent of Fusion depend on the propensity of the corresponding monolayers of Membranes to bend in the required directions.

Alexander Kros - One of the best experts on this subject based on the ideXlab platform.

  • Controlling the rate of coiled coil driven Membrane Fusion.
    Chemical Communications, 2013
    Co-Authors: Tingting Zheng, Hana Robson Marsden, Itsuro Tomatsu, Jens Voskuhl, Frank Versluis, Harshal Zope, Alexander Kros
    Abstract:

    Sets of complementary lipidated coiled-coil forming peptides that fuse Membrane Fusion have been designed. The influence of the coiled-coil motif on the rate of liposome Fusion was studied, by varying the number of heptad repeats. We found that an increased coiled-coil stability of complementary peptides translates into increased rates of Membrane Fusion of liposomes.

  • Model systems for Membrane Fusion.
    Chemical Society Reviews, 2010
    Co-Authors: Hana Robson Marsden, Itsuro Tomatsu, Alexander Kros
    Abstract:

    Membrane Fusion has an overarching influence on living organisms. The Fusion of sperm and egg Membranes initiates the life of a sexually reproducing organism. Intracellular Membrane Fusion facilitates molecular trafficking within every cell of the organism during its entire lifetime, and virus-cell Membrane Fusion may signal the end of the organism's life. Considering its importance, surprisingly little is known about the molecular-level mechanism of Membrane Fusion. Due to the complexity of a living cell, observations often leave room for ambiguity in interpretation. Therefore artificial model systems composed of only a few components are being used to further our understanding of controlled Fusion processes. In this critical review we first give an overview of the hypothesized mechanism of Membrane Fusion and the techniques that are used to investigate it, and then present a selection of non-targeted and targeted model systems, finishing with current applications and predictions on future developments (85 references).