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Akimov SA, Molotkovsky RJ, Kuzmin PI, Galimzyanov TR, Batishchev OV. Continuum Models of Membrane Fusion: Evolution of the Theory. Int J Mol Sci 2020; 21:E3875. [PMID: 32485905 PMCID: PMC7312925 DOI: 10.3390/ijms21113875] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 05/24/2020] [Accepted: 05/27/2020] [Indexed: 12/18/2022] Open
Abstract
Starting from fertilization, through tissue growth, hormone secretion, synaptic transmission, and sometimes morbid events of carcinogenesis and viral infections, membrane fusion regulates the whole life of high organisms. Despite that, a lot of fusion processes still lack well-established models and even a list of main actors. A merger of membranes requires their topological rearrangements controlled by elastic properties of a lipid bilayer. That is why continuum models based on theories of membrane elasticity are actively applied for the construction of physical models of membrane fusion. Started from the view on the membrane as a structureless film with postulated geometry of fusion intermediates, they developed along with experimental and computational techniques to a powerful tool for prediction of the whole process with molecular accuracy. In the present review, focusing on fusion processes occurring in eukaryotic cells, we scrutinize the history of these models, their evolution and complication, as well as open questions and remaining theoretical problems. We show that modern approaches in this field allow continuum models of membrane fusion to stand shoulder to shoulder with molecular dynamics simulations, and provide the deepest understanding of this process in multiple biological systems.
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Affiliation(s)
- Sergey A. Akimov
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia; (R.J.M.); (P.I.K.); (T.R.G.); (O.V.B.)
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Bompard J, Rosso A, Brizuela L, Mebarek S, Blum LJ, Trunfio-Sfarghiu AM, Lollo G, Granjon T, Girard-Egrot A, Maniti O. Membrane Fluidity as a New Means to Selectively Target Cancer Cells with Fusogenic Lipid Carriers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:5134-5144. [PMID: 32338922 DOI: 10.1021/acs.langmuir.0c00262] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Lipid-based carriers such as liposomes represent one of the most advanced classes of drug delivery systems. Their clinical success relies on their composition, similar to that of the cell membrane. Their cellular specificity often relies on a ligand-receptor interaction. Although differences in the physicochemical properties of the cell membrane between tumor and nontumor cells have been reported, they are not systematically used for drug delivery purposes. In this report, a new approach was developed to ensure selective targeting based on physical compatibility between the target and the carrier membranes. By modulating the liposome composition and thus its membrane fluidity, we achieved selective targeting on four cancer cell lines of varying aggressiveness. Furthermore, using membrane-embedded and inner core-encapsulated fluorophores, we assessed the mechanism of this interaction to be based on the fusion of the liposome with the cell membranes. Membrane fluidity is therefore a major parameter to be considered when designing lipid drug carriers as a promising, lower cost alternative to current targeting strategies based on covalent grafting.
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Affiliation(s)
- Julien Bompard
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, ICBMS UMR 5246, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Annalisa Rosso
- Laboratoire d'Automatique, de Génie des Procédés et de Génie PharmaceutiqueLAGEPP UMR 5007, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Leyre Brizuela
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, ICBMS UMR 5246, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Saïda Mebarek
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, ICBMS UMR 5246, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Loïc J Blum
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, ICBMS UMR 5246, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Ana-Maria Trunfio-Sfarghiu
- Laboratoire de Mécanique des Contacts et Structures, LaMCoS UMR 5259, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Giovanna Lollo
- Laboratoire d'Automatique, de Génie des Procédés et de Génie PharmaceutiqueLAGEPP UMR 5007, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Thierry Granjon
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, ICBMS UMR 5246, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Agnès Girard-Egrot
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, ICBMS UMR 5246, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
| | - Ofelia Maniti
- Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, ICBMS UMR 5246, CNRS, Univ Lyon, Université Lyon 1, Lyon, France
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53
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Bruininks BM, Souza PC, Ingolfsson H, Marrink SJ. A molecular view on the escape of lipoplexed DNA from the endosome. eLife 2020; 9:52012. [PMID: 32297853 PMCID: PMC7170654 DOI: 10.7554/elife.52012] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 02/24/2020] [Indexed: 12/23/2022] Open
Abstract
The use of non-viral vectors for in vivo gene therapy could drastically increase safety, whilst reducing the cost of preparing the vectors. A promising approach to non-viral vectors makes use of DNA/cationic liposome complexes (lipoplexes) to deliver the genetic material. Here we use coarse-grained molecular dynamics simulations to investigate the molecular mechanism underlying efficient DNA transfer from lipoplexes. Our computational fusion experiments of lipoplexes with endosomal membrane models show two distinct modes of transfection: parallel and perpendicular. In the parallel fusion pathway, DNA aligns with the membrane surface, showing very quick release of genetic material shortly after the initial fusion pore is formed. The perpendicular pathway also leads to transfection, but release is slower. We further show that the composition and size of the lipoplex, as well as the lipid composition of the endosomal membrane, have a significant impact on fusion efficiency in our models.
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Affiliation(s)
- Bart Mh Bruininks
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh, Netherlands
| | - Paulo Ct Souza
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh, Netherlands
| | - Helgi Ingolfsson
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh, Netherlands
| | - Siewert J Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh, Netherlands
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54
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Benhaim MA, Lee KK. New Biophysical Approaches Reveal the Dynamics and Mechanics of Type I Viral Fusion Machinery and Their Interplay with Membranes. Viruses 2020; 12:E413. [PMID: 32276357 PMCID: PMC7232462 DOI: 10.3390/v12040413] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 04/04/2020] [Accepted: 04/04/2020] [Indexed: 12/27/2022] Open
Abstract
Protein-mediated membrane fusion is a highly regulated biological process essential for cellular and organismal functions and infection by enveloped viruses. During viral entry the membrane fusion reaction is catalyzed by specialized protein machinery on the viral surface. These viral fusion proteins undergo a series of dramatic structural changes during membrane fusion where they engage, remodel, and ultimately fuse with the host membrane. The structural and dynamic nature of these conformational changes and their impact on the membranes have long-eluded characterization. Recent advances in structural and biophysical methodologies have enabled researchers to directly observe viral fusion proteins as they carry out their functions during membrane fusion. Here we review the structure and function of type I viral fusion proteins and mechanisms of protein-mediated membrane fusion. We highlight how recent technological advances and new biophysical approaches are providing unprecedented new insight into the membrane fusion reaction.
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Affiliation(s)
- Mark A. Benhaim
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA;
| | - Kelly K. Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA;
- Biological Physics Structure and Design Program, University of Washington, Seattle, WA 98195-7610, USA
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55
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Target Membrane Cholesterol Modulates Single Influenza Virus Membrane Fusion Efficiency but Not Rate. Biophys J 2020; 118:2426-2433. [PMID: 32298636 DOI: 10.1016/j.bpj.2020.03.021] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 03/09/2020] [Accepted: 03/23/2020] [Indexed: 12/11/2022] Open
Abstract
Host lipid composition influences many stages of the influenza A virus (IAV) entry process, including initial binding of IAV to sialylated glycans, fusion between the viral envelope and the host membrane, and the formation of a fusion pore through which the viral genome is transferred into a target cell. In particular, target membrane cholesterol has been shown to preferentially associate with virus receptors and alter physical properties of the membrane like fluidity and curvature. These properties affect both IAV binding and fusion, which makes it difficult to isolate the role of cholesterol in IAV fusion from receptor binding effects. Here, we develop a fusion assay that uses synthetic DNA-lipid conjugates as surrogate viral receptors to tether virions to target vesicles. To avoid the possibly perturbative effect of adding a self-quenched concentration of dye-labeled lipids to the viral membrane, we tether virions to lipid-labeled target vesicles and use fluorescence microscopy to detect individual, pH-triggered IAV membrane fusion events. Through this approach, we find that cholesterol in the target membrane enhances the efficiency of single-particle IAV lipid mixing, whereas the rate of lipid mixing is independent of cholesterol composition. We also find that the single-particle kinetics of influenza lipid mixing to target membranes with different cholesterol compositions is independent of receptor binding, suggesting that cholesterol-mediated spatial clustering of viral receptors within the target membrane does not significantly affect IAV hemifusion. These results are consistent with the hypothesis that target membrane cholesterol increases lipid mixing efficiency by altering host membrane curvature.
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56
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Kim M, Porras-Gomez M, Leal C. Graphene-based sensing of oxygen transport through pulmonary membranes. Nat Commun 2020; 11:1103. [PMID: 32107376 PMCID: PMC7046670 DOI: 10.1038/s41467-020-14825-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Accepted: 02/04/2020] [Indexed: 11/09/2022] Open
Abstract
Lipid-protein complexes are the basis of pulmonary surfactants covering the respiratory surface and mediating gas exchange in lungs. Cardiolipin is a mitochondrial lipid overexpressed in mammalian lungs infected by bacterial pneumonia. In addition, increased oxygen supply (hyperoxia) is a pathological factor also critical in bacterial pneumonia. In this paper we fabricate a micrometer-size graphene-based sensor to measure oxygen permeation through pulmonary membranes. Combining oxygen sensing, X-ray scattering, and Atomic Force Microscopy, we show that mammalian pulmonary membranes suffer a structural transformation induced by cardiolipin. We observe that cardiolipin promotes the formation of periodic protein-free inter-membrane contacts with rhombohedral symmetry. Membrane contacts, or stalks, promote a significant increase in oxygen gas permeation which may bear significance for alveoli gas exchange imbalance in pneumonia.
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Affiliation(s)
- Mijung Kim
- Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Marilyn Porras-Gomez
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Cecilia Leal
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
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57
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Zhukovsky MA, Filograna A, Luini A, Corda D, Valente C. Phosphatidic acid in membrane rearrangements. FEBS Lett 2019; 593:2428-2451. [PMID: 31365767 DOI: 10.1002/1873-3468.13563] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/25/2019] [Accepted: 07/26/2019] [Indexed: 12/16/2022]
Abstract
Phosphatidic acid (PA) is the simplest cellular glycerophospholipid characterized by unique biophysical properties: a small headgroup; negative charge; and a phosphomonoester group. Upon interaction with lysine or arginine, PA charge increases from -1 to -2 and this change stabilizes protein-lipid interactions. The biochemical properties of PA also allow interactions with lipids in several subcellular compartments. Based on this feature, PA is involved in the regulation and amplification of many cellular signalling pathways and functions, as well as in membrane rearrangements. Thereby, PA can influence membrane fusion and fission through four main mechanisms: it is a substrate for enzymes producing lipids (lysophosphatidic acid and diacylglycerol) that are involved in fission or fusion; it contributes to membrane rearrangements by generating negative membrane curvature; it interacts with proteins required for membrane fusion and fission; and it activates enzymes whose products are involved in membrane rearrangements. Here, we discuss the biophysical properties of PA in the context of the above four roles of PA in membrane fusion and fission.
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Affiliation(s)
- Mikhail A Zhukovsky
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Angela Filograna
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Alberto Luini
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Daniela Corda
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
| | - Carmen Valente
- Institute of Protein Biochemistry and Institute of Biochemistry and Cell Biology, National Research Council, Naples, Italy
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58
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Abstract
With no limiting membrane surrounding virions, nonenveloped viruses have no need for membrane fusion to gain access to intracellular replication compartments. Consequently, nonenveloped viruses do not encode membrane fusion proteins. The only exception to this dogma is the fusogenic reoviruses that encode fusion-associated small transmembrane (FAST) proteins that induce syncytium formation. FAST proteins are the smallest viral membrane fusion proteins and, unlike their enveloped virus counterparts, are nonstructural proteins that evolved specifically to induce cell-to-cell, not virus-cell, membrane fusion. This distinct evolutionary imperative is reflected in structural and functional features that distinguish this singular family of viral fusogens from all other protein fusogens. These rudimentary fusogens comprise specific combinations of different membrane effector motifs assembled into small, modular membrane fusogens. FAST proteins offer a minimalist model to better understand the ubiquitous process of protein-mediated membrane fusion and to reveal novel mechanisms of nonenveloped virus dissemination that contribute to virulence.
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Affiliation(s)
- Roy Duncan
- Department of Microbiology & Immunology, Department of Biochemistry & Molecular Biology, and Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4R2;
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59
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Komorowski K, Salditt A, Xu Y, Yavuz H, Brennich M, Jahn R, Salditt T. Vesicle Adhesion and Fusion Studied by Small-Angle X-Ray Scattering. Biophys J 2019; 114:1908-1920. [PMID: 29694868 PMCID: PMC5936998 DOI: 10.1016/j.bpj.2018.02.040] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 02/19/2018] [Accepted: 02/28/2018] [Indexed: 12/02/2022] Open
Abstract
We have studied the adhesion state (also denoted by docking state) of lipid vesicles as induced by the divalent ions Ca2+ or Mg2+ at well-controlled ion concentration, lipid composition, and charge density. The bilayer structure and the interbilayer distance in the docking state were analyzed by small-angle x-ray scattering. A strong adhesion state was observed for DOPC:DOPS vesicles, indicating like-charge attraction resulting from ion correlations. The observed interbilayer separations of ∼1.6 nm agree quantitatively with the predictions of electrostatics in the strong coupling regime. Although this phenomenon was observed when mixing anionic and zwitterionic (or neutral) lipids, pure anionic membranes (DOPS) with highest charge density σ resulted in a direct phase transition to a multilamellar state, which must be accompanied by rupture and fusion of vesicles. To extend the structural assay toward protein-controlled docking and fusion, we have characterized reconstituted N-ethylmaleimide-sensitive factor attachment protein receptors in controlled proteoliposome suspensions by small-angle x-ray scattering.
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Affiliation(s)
- Karlo Komorowski
- Institut für Röntgenphysik, Georg-August-Universität Göttingen, Göttingen, Germany; Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Annalena Salditt
- Institut für Röntgenphysik, Georg-August-Universität Göttingen, Göttingen, Germany
| | - Yihui Xu
- Institut für Röntgenphysik, Georg-August-Universität Göttingen, Göttingen, Germany
| | - Halenur Yavuz
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Martha Brennich
- European Molecular Biology Laboratory, Grenoble Outstation, Grenoble, France
| | - Reinhard Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Tim Salditt
- Institut für Röntgenphysik, Georg-August-Universität Göttingen, Göttingen, Germany.
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60
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Abstract
Force spectroscopy allows the manipulation of single molecules and the characterization of their properties and interactions thereby rendering it a powerful tool for biological sciences. Force spectroscopy at the level of individual molecules requires force resolution in the piconewton regime as achieved by optical tweezers (OT), magnetic tweezers (MT), and atomic force microscopy (AFM) with AFM providing the largest force range from tenth of piconewton to several micronewton. In membrane probe spectroscopy the commonly used sharp cantilever tip is replaced by a lipid-coated glass sphere. This technique expands the scope of force spectroscopy to processes at and between lipid bilayers, like the formation of coiled coils between SNARE (soluble N-ethylmaleimide-sensitive factor attachment receptor) proteins as well as subsequent membrane fusion. To this end, two solid-supported membranes equipped with SNARE proteins or fusion peptides are separately deposited on a flat glassy surface and on a micrometer glass sphere attached to the end of a tipless AFM cantilever. These two membranes are rapidly brought into contact until a defined force is reached. The AFM deflection readout is used to monitor the distance between the two bilayers, which allows to observe and identify fusion processes of the two lipid membranes, while the forces needed to separate the two surfaces give insights into the formation of SNARE complexes. By changing the contact pressure one can access fusion kinetics and to some extent reconstruct the energy landscape of membrane fusion. In this chapter we describe the preparation of membrane-coated colloidal probes attached to AFM cantilevers, experimental procedures, and necessary data analysis to perform membrane probe spectroscopy in the presence of fusogenic peptides or proteins.
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61
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Brunger AT, Choi UB, Lai Y, Leitz J, White KI, Zhou Q. The pre-synaptic fusion machinery. Curr Opin Struct Biol 2019; 54:179-188. [PMID: 30986753 PMCID: PMC6939388 DOI: 10.1016/j.sbi.2019.03.007] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2019] [Revised: 03/02/2019] [Accepted: 03/06/2019] [Indexed: 11/26/2022]
Abstract
Here, we review recent insights into the neuronal presynaptic fusion machinery that releases neurotransmitter molecules into the synaptic cleft upon stimulation. The structure of the pre-fusion state of the SNARE/complexin-1/synaptotagmin-1 synaptic protein complex suggests a new model for the initiation of fast Ca2+-triggered membrane fusion. Functional studies have revealed roles of the essential factors Munc18 and Munc13, demonstrating that a part of their function involves the proper assembly of synaptic protein complexes. Near-atomic resolution structures of the NSF/αSNAP/SNARE complex provide first glimpses of the molecular machinery that disassembles the SNARE complex during the synaptic vesicle cycle. These structures show how this machinery captures the SNARE substrate and provide clues as to a possible processing mechanism.
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Affiliation(s)
- Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, USA; Department of Structural Biology, Stanford University, Stanford, USA; Department of Photon Science, Stanford University, Stanford, USA; Howard Hughes Medical Institute, Stanford University, Stanford, USA.
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, USA; Department of Structural Biology, Stanford University, Stanford, USA; Department of Photon Science, Stanford University, Stanford, USA; Howard Hughes Medical Institute, Stanford University, Stanford, USA
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, USA; Department of Structural Biology, Stanford University, Stanford, USA; Department of Photon Science, Stanford University, Stanford, USA; Howard Hughes Medical Institute, Stanford University, Stanford, USA
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, USA; Department of Structural Biology, Stanford University, Stanford, USA; Department of Photon Science, Stanford University, Stanford, USA; Howard Hughes Medical Institute, Stanford University, Stanford, USA
| | - Kristopher Ian White
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, USA; Department of Structural Biology, Stanford University, Stanford, USA; Department of Photon Science, Stanford University, Stanford, USA; Howard Hughes Medical Institute, Stanford University, Stanford, USA
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, USA; Department of Structural Biology, Stanford University, Stanford, USA; Department of Photon Science, Stanford University, Stanford, USA; Howard Hughes Medical Institute, Stanford University, Stanford, USA
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62
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Smirnova YG, Risselada HJ, Müller M. Thermodynamically reversible paths of the first fusion intermediate reveal an important role for membrane anchors of fusion proteins. Proc Natl Acad Sci U S A 2019; 116:2571-2576. [PMID: 30700547 PMCID: PMC6377489 DOI: 10.1073/pnas.1818200116] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Biological membrane fusion proceeds via an essential topological transition of the two membranes involved. Known players such as certain lipid species and fusion proteins are generally believed to alter the free energy and thus the rate of the fusion reaction. Quantifying these effects by theory poses a major challenge since the essential reaction intermediates are collective, diffusive and of a molecular length scale. We conducted molecular dynamics simulations in conjunction with a state-of-the-art string method to resolve the minimum free-energy path of the first fusion intermediate state, the so-called stalk. We demonstrate that the isolated transmembrane domains (TMDs) of fusion proteins such as SNARE molecules drastically lower the free energy of both the stalk barrier and metastable stalk, which is not trivially explained by molecular shape arguments. We relate this effect to the local thinning of the membrane (negative hydrophobic mismatch) imposed by the TMDs which favors the nearby presence of the highly bent stalk structure or prestalk dimple. The distance between the membranes is the most crucial determinant of the free energy of the stalk, whereas the free-energy barrier changes only slightly. Surprisingly, fusion enhancing lipids, i.e., lipids with a negative spontaneous curvature, such as PE lipids have little effect on the free energy of the stalk barrier, likely because of its single molecular nature. In contrast, the lipid shape plays a crucial role in overcoming the hydration repulsion between two membranes and thus rather lowers the total work required to form a stalk.
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Affiliation(s)
- Yuliya G Smirnova
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany;
| | - Herre Jelger Risselada
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
- Leiden Institute of Chemistry, Leiden University, 2333 CC Leiden, The Netherlands
| | - Marcus Müller
- Institute for Theoretical Physics, Georg-August University, 37077 Göttingen, Germany
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63
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Abstract
Mitochondria undergo frequent fusion and fission events to adapt their morphology to cellular needs. Homotypic docking and fusion of outer mitochondrial membranes are controlled by Mitofusins, a set of large membrane-anchored GTPase proteins belonging to the dynamin superfamily. Mitofusins include, in addition to their GTPase and transmembrane domains, two heptad repeat domains, HR1 and HR2. All four regions are crucial for Mitofusin function, but their precise contribution to mitochondrial docking and fusion events has remained elusive until very recently. In this commentary, we first give an overview of the established strategies employed by various protein machineries distinct from Mitofusins to mediate membrane fusion. We then present recent structure–function data on Mitofusins that provide important novel insights into their mode of action in mitochondrial fusion.
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Affiliation(s)
- Mickael M Cohen
- Sorbonne Université, CNRS UMR8226, Institut de Biologie Physico-Chimique, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Paris, France
| | - David Tareste
- Université Paris Descartes, Sorbonne Paris Cité, INSERM ERL U950, Trafic Membranaire dans le Cerveau Normal et Pathologique, Paris, France.,Université Paris Descartes, Sorbonne Paris Cité, INSERM UMR 894, Institut de Psychiatrie et Neurosciences de Paris, Paris, France
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64
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Qian S, Rai DK. Grazing-Angle Neutron Diffraction Study of the Water Distribution in Membrane Hemifusion: From the Lamellar to Rhombohedral Phase. J Phys Chem Lett 2018; 9:5778-5784. [PMID: 30111108 DOI: 10.1021/acs.jpclett.8b01602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The water distribution between lipid bilayers is important in understanding the role of the hydration force at different steps of the membrane fusion pathway. In this study, we used grazing-angle neutron diffraction to map out the water distribution in lipid bilayers transiting from a lamellar structure to the hemifusion "stalk" structure in a rhombohedral phase. Under osmotic pressure exerted by different levels of relative humidity, the lipid membrane sample was maintained in equilibrium at different lattices suitable for neutron diffraction. The D2O used to hydrate the lipid membrane sample stood out from the lipid in the reconstructed structure because of its much higher coherent neutron scattering length density. The density map indicates that water dissociated from the headgroup in the lamellar phase. In the rhombohedral phase, water was significantly reduced and was squeezed into pockets around the stalk. This study complements earlier structural studies by grazing-angle X-ray diffraction, which is sensitive to only the parts of the structure with high electron density (such as phosphors). The experiment also demonstrated that the recently developed time-of-flight small-angle neutron scattering beamline at the Spallation Neutron Source is suitable for grazing-angle neutron diffraction to provide the structures of large unit cells on the order of a few nanometers, such as biomembrane structures.
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65
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66
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Brunger AT, Leitz J, Zhou Q, Choi UB, Lai Y. Ca 2+-Triggered Synaptic Vesicle Fusion Initiated by Release of Inhibition. Trends Cell Biol 2018; 28:631-645. [PMID: 29706534 PMCID: PMC6056330 DOI: 10.1016/j.tcb.2018.03.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 03/17/2018] [Accepted: 03/26/2018] [Indexed: 12/20/2022]
Abstract
Recent structural and functional studies of the synaptic vesicle fusion machinery suggest an inhibited tripartite complex consisting of neuronal soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs), synaptotagmin, and complexin prior to Ca2+-triggered synaptic vesicle fusion. We speculate that Ca2+-triggered fusion commences with the release of inhibition by Ca2+ binding to synaptotagmin C2 domains. Subsequently, fusion is assisted by SNARE complex zippering and by active membrane remodeling properties of synaptotagmin. This additional, inhibitory role of synaptotagmin may be a general principle since other recent studies suggest that Ca2+ binding to extended synaptotagmin C2 domains enables lipid transport by releasing an inhibited state of the system, and that Munc13 may nominally be in an inhibited state, which is released upon Ca2+ binding to one of its C2 domains.
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Affiliation(s)
- Axel T Brunger
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA.
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA; Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA; Department of Structural Biology, Stanford University, Stanford, CA, USA; Department of Photon Science, Stanford University, Stanford, CA, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA
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67
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Bassereau P, Jin R, Baumgart T, Deserno M, Dimova R, Frolov VA, Bashkirov PV, Grubmüller H, Jahn R, Risselada HJ, Johannes L, Kozlov MM, Lipowsky R, Pucadyil TJ, Zeno WF, Stachowiak JC, Stamou D, Breuer A, Lauritsen L, Simon C, Sykes C, Voth GA, Weikl TR. The 2018 biomembrane curvature and remodeling roadmap. JOURNAL OF PHYSICS D: APPLIED PHYSICS 2018; 51:343001. [PMID: 30655651 PMCID: PMC6333427 DOI: 10.1088/1361-6463/aacb98] [Citation(s) in RCA: 161] [Impact Index Per Article: 26.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The importance of curvature as a structural feature of biological membranes has been recognized for many years and has fascinated scientists from a wide range of different backgrounds. On the one hand, changes in membrane morphology are involved in a plethora of phenomena involving the plasma membrane of eukaryotic cells, including endo- and exocytosis, phagocytosis and filopodia formation. On the other hand, a multitude of intracellular processes at the level of organelles rely on generation, modulation, and maintenance of membrane curvature to maintain the organelle shape and functionality. The contribution of biophysicists and biologists is essential for shedding light on the mechanistic understanding and quantification of these processes. Given the vast complexity of phenomena and mechanisms involved in the coupling between membrane shape and function, it is not always clear in what direction to advance to eventually arrive at an exhaustive understanding of this important research area. The 2018 Biomembrane Curvature and Remodeling Roadmap of Journal of Physics D: Applied Physics addresses this need for clarity and is intended to provide guidance both for students who have just entered the field as well as established scientists who would like to improve their orientation within this fascinating area.
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Affiliation(s)
- Patricia Bassereau
- Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005 Paris, France
- Sorbonne Université, 75005 Paris, France
| | - Rui Jin
- Chemistry Department, University of Pennsylvania, Philadelphia, PA 19104-6323, United States of America
| | - Tobias Baumgart
- Chemistry Department, University of Pennsylvania, Philadelphia, PA 19104-6323, United States of America
| | - Markus Deserno
- Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, United States of America
| | - Rumiana Dimova
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
| | - Vadim A Frolov
- Biofisika Institute (CSIC, UPV/EHU) and Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa 48940, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao 48013, Spain
| | - Pavel V Bashkirov
- Federal Research and Clinical Centre of Physical-Chemical Medicine, Moscow 119435, Russia
- A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow 119071, Russia
| | - Helmut Grubmüller
- Department of Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - H Jelger Risselada
- Department of Theoretical Physics, Georg-August University, Göttingen, Germany
| | - Ludger Johannes
- Cellular and Chemical Biology Unit, Institut Curie, PSL Research University, U1143 INSERM, UMR3666 CNRS, 26 rue d'Ulm, 75248 Paris Cedex 05, France
| | - Michael M Kozlov
- Sackler Faculty of Medicine, Department of Physiology and Pharmacology, Tel Aviv University
| | - Reinhard Lipowsky
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
| | | | - Wade F Zeno
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX, United States of America
| | - Jeanne C Stachowiak
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX, United States of America
- University of Texas at Austin, Institute for Cellular and Molecular Biology, Austin, TX, United States of America
| | - Dimitrios Stamou
- Bionanotechnology and Nanomedicine Laboratory, Department of Chemistry, Nano-Science Center, University of Copenhagen, Denmark
| | - Artú Breuer
- Bionanotechnology and Nanomedicine Laboratory, Department of Chemistry, Nano-Science Center, University of Copenhagen, Denmark
| | - Line Lauritsen
- Bionanotechnology and Nanomedicine Laboratory, Department of Chemistry, Nano-Science Center, University of Copenhagen, Denmark
| | - Camille Simon
- Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005 Paris, France
- Sorbonne Université, 75005 Paris, France
| | - Cécile Sykes
- Laboratoire Physico Chimie Curie, Institut Curie, PSL Research University, CNRS UMR168, 75005 Paris, France
- Sorbonne Université, 75005 Paris, France
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL, United States of America
| | - Thomas R Weikl
- Department of Theory and Bio-Systems, Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
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68
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PAMAM dendrimer - cell membrane interactions. Adv Colloid Interface Sci 2018; 257:1-18. [PMID: 30008347 DOI: 10.1016/j.cis.2018.06.005] [Citation(s) in RCA: 126] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 06/20/2018] [Accepted: 06/21/2018] [Indexed: 12/16/2022]
Abstract
PAMAM dendrimers have been conjectured for a wide range of biomedical applications due to their tuneable physicochemical properties. However, their application has been hindered by uncertainties in their cytotoxicity, which is influenced by dendrimer generation (i.e. size and surface group density), surface chemistry, and dosage, as well as cell specificity. In this review, biomedical applications of polyamidoamine (PAMAM) dendrimers and some related cytotoxicity studies are first outlined. Alongside these in vitro experiments, lipid membranes such as supported lipid bilayers (SLBs), liposomes, and Langmuir monolayers have been used as cell membrane models to study PAMAM dendrimer-membrane interactions. Related experimental and theoretical studies are summarized, and the physical insights from these studies are discussed to shed light on the fundamental understanding of PAMAM dendrimer-cell membrane interactions. We conclude with a summary of some questions that call for further investigations.
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69
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Steer D, Leung SSW, Meiselman H, Topgaard D, Leal C. Structure of Lung-Mimetic Multilamellar Bodies with Lipid Compositions Relevant in Pneumonia. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:7561-7574. [PMID: 29847137 DOI: 10.1021/acs.langmuir.8b01359] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The hierarchical assembly of lipids, as modulated by composition and environment, plays a significant role in the function of biological membranes and a myriad of diseases. Elevated concentrations of calcium ions and cardiolipin (CL), an anionic tetra-alkyl lipid found in mitochondria and some bacterial cell membranes, have been implicated in pneumonia recently. However, their impact on the physicochemical properties of lipid assemblies in lungs and how it impairs alveoli function is still unknown. We use small- and wide-angle X-ray scattering (S/WAXS) and solid-state nuclear magnetic resonance (ssNMR) to probe the structure and dynamics of lung-mimetic multilamellar bodies (MLBs) in the presence of Ca2+ and CL. We conjecture that CL overexpressed in the hypophase of alveoli strongly affects the structure of lung-lipid bilayers and their stacking in the MLBs. Specifically, S/WAXS data revealed that CL induces significant shrinkage of the water-layer separating the concentric bilayers in multilamellar aggregates. ssNMR measurements indicate that this interbilayer tightening is due to undulation repulsion damping as CL renders the glycerol backbone of the membranes significantly more static. In addition to MLB dehydration, CL promotes intrabilayer phase separation into saturated-rich and unsaturated-rich lipid domains that couple across multiple layers. Expectedly, addition of Ca2+ screens the electrostatic repulsion between negatively charged lung membranes. However, when CL is present, addition of Ca2+ results in an apparent interbilayer expansion likely due to local structural defects. Combining S/WAXS and ssNMR on systems with compositions pertinent to healthy and unhealthy lung membranes, we propose how alteration of the physiochemical properties of MLBs can critically impact the breathing cycle.
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Affiliation(s)
| | | | | | - Daniel Topgaard
- Division of Physical Chemistry, Center of Chemistry and Chemical Engineering , Lund University , SE-221 00 Lund , Sweden
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70
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Abstract
This review summarizes current knowledge of synaptic proteins that are central to synaptic vesicle fusion in presynaptic active zones, including SNAREs (soluble N-ethylmaleimide sensitive factor attachment protein receptors), synaptotagmin, complexin, Munc18 (mammalian uncoordinated-18), and Munc13 (mammalian uncoordinated-13), and highlights recent insights in the cooperation of these proteins for neurotransmitter release. Structural and functional studies of the synaptic fusion machinery suggest new molecular models of synaptic vesicle priming and Ca2+-triggered fusion. These studies will be a stepping-stone toward answering the question of how the synaptic vesicle fusion machinery achieves such high speed and sensitivity.
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Affiliation(s)
- Axel T Brunger
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
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71
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Molotkovsky RJ, Alexandrova VV, Galimzyanov TR, Jiménez-Munguía I, Pavlov KV, Batishchev OV, Akimov SA. Lateral Membrane Heterogeneity Regulates Viral-Induced Membrane Fusion during HIV Entry. Int J Mol Sci 2018; 19:ijms19051483. [PMID: 29772704 PMCID: PMC5983600 DOI: 10.3390/ijms19051483] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2018] [Revised: 05/08/2018] [Accepted: 05/14/2018] [Indexed: 11/16/2022] Open
Abstract
Sphingomyelin- and cholesterol- enriched membrane domains, commonly referred to as “rafts” play a crucial role in a large number of intra- and intercellular processes. Recent experiments suggest that not only the volumetric inhomogeneity of lipid distribution in rafts, but also the arrangement of the 1D boundary between the raft and the surrounding membrane is important for the membrane-associated processes. The reason is that the boundary preferentially recruits different peptides, such as HIV (human immunodeficiency virus) fusion peptide. In the present work, we report a theoretical investigation of mechanisms of influence of the raft boundary arrangement upon virus-induced membrane fusion. We theoretically predict that the raft boundary can act as an attractor for viral fusion peptides, which preferentially distribute into the vicinity of the boundary, playing the role of ‘line active components’ of the membrane (‘linactants’). We have calculated the height of the fusion energy barrier and demonstrated that, in the case of fusion between HIV membrane and the target cell, presence of the raft boundary in the vicinity of the fusion site facilitates fusion. The results we obtained can be further generalized to be applicable to other enveloped viruses.
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Affiliation(s)
- Rodion J Molotkovsky
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia.
| | - Veronika V Alexandrova
- Faculty of Physics, M.V. Lomonosov Moscow State University, 1-2 Leninskie Gory, 119991 Moscow, Russia.
| | - Timur R Galimzyanov
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia.
- Department of Theoretical Physics and Quantum Technologies, National University of Science and Technology "MISiS", 4 Leninskiy Prospekt, 119049 Moscow, Russia.
| | - Irene Jiménez-Munguía
- Department of Engineering of Technological Equipment, National University of Science and Technology "MISiS", 4 Leninskiy Prospekt, 119049 Moscow, Russia.
| | - Konstantin V Pavlov
- Laboratory of Electrophysiology, Federal Clinical Center of Physical-Chemical Medicine of FMBA, 1a Malaya Pirogovskaya Street, 119435 Moscow, Russia.
| | - Oleg V Batishchev
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia.
- Department of Physics of Living Systems, Moscow Institute of Physics and Technology (State University), 9 Institutskiy Lane, Dolgoprudniy, 141700 Moscow Region, Russia.
| | - Sergey A Akimov
- Laboratory of Bioelectrochemistry, A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31/4 Leninskiy Prospekt, 119071 Moscow, Russia.
- Department of Theoretical Physics and Quantum Technologies, National University of Science and Technology "MISiS", 4 Leninskiy Prospekt, 119049 Moscow, Russia.
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72
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Seiwert D, Witt H, Ritz S, Janshoff A, Paulsen H. The Nonbilayer Lipid MGDG and the Major Light-Harvesting Complex (LHCII) Promote Membrane Stacking in Supported Lipid Bilayers. Biochemistry 2018; 57:2278-2288. [PMID: 29577715 DOI: 10.1021/acs.biochem.8b00118] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The thylakoid membrane of algae and land plants is characterized by its intricate architecture, comprising tightly appressed membrane stacks termed grana. The contributions of individual components to grana stack formation are not yet fully elucidated. As an in vitro model, we use supported lipid bilayers made of thylakoid lipid mixtures to study the effect of major light-harvesting complex (LHCII), different lipids, and ions on membrane stacking, seen as elevated structures forming on top of the planar membrane surface in the presence of LHCII protein. These structures were examined by confocal laser scanning microscopy, atomic force microscopy, and fluorescence recovery after photobleaching, revealing multilamellar LHCII-membrane stacks composed of connected lipid bilayers. Both native-like and non-native interactions between the LHCII complexes may contribute to membrane appression in the supported bilayers. However, applying in vivo-like salt conditions to uncharged glycolipid membranes drastically increased the level of stack formation due to enforced LHCII-LHCII interactions, which is in line with recent crystallographic and cryo-electron microscopic data [Wan, T., et al. (2014) Mol. Plant 7, 916-919; Albanese, P., et al. (2017) Sci. Rep. 7, 10067-10083]. Furthermore, we observed the nonbilayer lipid MGDG to strongly promote membrane stacking, pointing to the long-term proposed function of MGDG in stabilizing the inner membrane leaflet of highly curved margins in the periphery of each grana disc because of its negative intrinsic curvature [Murphy, D. J. (1982) FEBS Lett. 150, 19-26].
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Affiliation(s)
- Dennis Seiwert
- Institute of Molecular Physiology , Johannes Gutenberg University Mainz , Johannes-von-Müller-Weg 6 , 55128 Mainz , Germany
| | - Hannes Witt
- Institute of Physical Chemistry , University of Goettingen , Tammannstrasse 6 , 37077 Goettingen , Germany
| | - Sandra Ritz
- Microscopy Core Facility , Institute of Molecular Biology , Ackermannweg 4 , 55128 Mainz , Germany
| | - Andreas Janshoff
- Institute of Physical Chemistry , University of Goettingen , Tammannstrasse 6 , 37077 Goettingen , Germany
| | - Harald Paulsen
- Institute of Molecular Physiology , Johannes Gutenberg University Mainz , Johannes-von-Müller-Weg 6 , 55128 Mainz , Germany
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73
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Boonstra S, Blijleven JS, Roos WH, Onck PR, van der Giessen E, van Oijen AM. Hemagglutinin-Mediated Membrane Fusion: A Biophysical Perspective. Annu Rev Biophys 2018; 47:153-173. [PMID: 29494252 DOI: 10.1146/annurev-biophys-070317-033018] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Influenza hemagglutinin (HA) is a viral membrane protein responsible for the initial steps of the entry of influenza virus into the host cell. It mediates binding of the virus particle to the host-cell membrane and catalyzes fusion of the viral membrane with that of the host. HA is therefore a major target in the development of antiviral strategies. The fusion of two membranes involves high activation barriers and proceeds through several intermediate states. Here, we provide a biophysical description of the membrane fusion process, relating its kinetic and thermodynamic properties to the large conformational changes taking place in HA and placing these in the context of multiple HA proteins working together to mediate fusion. Furthermore, we highlight the role of novel single-particle experiments and computational approaches in understanding the fusion process and their complementarity with other biophysical approaches.
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Affiliation(s)
- Sander Boonstra
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands; , , , ,
| | - Jelle S Blijleven
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands; , , , ,
| | - Wouter H Roos
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands; , , , ,
| | - Patrick R Onck
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands; , , , ,
| | - Erik van der Giessen
- Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands; , , , ,
| | - Antoine M van Oijen
- School of Chemistry; Faculty of Science, Medicine and Health; University of Wollongong, Wollongong, New South Wales 2522, Australia;
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74
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Singh P, Hui CY. Hydrodynamics govern the pre-fusion docking time of synaptic vesicles. J R Soc Interface 2018; 15:rsif.2017.0818. [PMID: 29386403 DOI: 10.1098/rsif.2017.0818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 01/09/2018] [Indexed: 11/12/2022] Open
Abstract
Synaptic vesicle fusion is a crucial step in the neurotransmission process. Neurotransmitter-filled vesicles are pre-docked at the synapse by the mediation of ribbon structures and SNARE proteins at the ribbon synapses. An electrical impulse triggers the fusion process of pre-docked vesicles, leading to the formation of a fusion pore and subsequently resulting in the release of neurotransmitter into the synaptic cleft. In this study, a continuum model of lipid membrane along with lubrication theory is used to determine the traverse time of the synaptic vesicle under the influence of hydrodynamic forces. We find that the traverse time is strongly dependent on how fast the driving force decays or grows with closure of the gap between the vesicle and the plasma membrane. If the correct behaviour is chosen, the traverse time obtained is of the order of a few hundred milliseconds and lies within the experimentally obtained value of approximately 250 ms (Zenisek D, Steyer JA, Almers W. 2000 Nature406, 849-854 (doi:10.1038/35022500)). We hypothesize that there are two different force behaviours, which complies with the experimental findings of pre-fusion docking of synaptic vesicles at the ribbon synapses. The common theme in the proposed force models is that the driving force has to very rapidly increase or decrease with the amount of clamping.
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Affiliation(s)
- Pankaj Singh
- Department of Theoretical and Applied Mechanics, Cornell University, Ithaca, NY 14853, USA
| | - Chung-Yuen Hui
- Department of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA
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75
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Carravilla P, Nieva JL. HIV antivirals: targeting the functional organization of the lipid envelope. Future Virol 2018. [DOI: 10.2217/fvl-2017-0114] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Most of the surface of the lipid bilayer covering the human immunodeficiency virus type 1 (HIV-1) particle is directly accessible from the aqueous medium. Its peculiar chemical composition and physical properties appear to be critical for infection and, therefore, may comprise a target for selective antiviral activity. The HIV-1 membrane is enriched in raft-type lipids and also displays aminophospholipids on its external leaflet. We contend here that a great deal of membrane-active compounds described to block HIV-1 infection can do so by following a common mechanism of action: alteration of the lateral heterogeneity that supports the functional organization of the lipid envelope. The confirmation of this hypothesis could lay new foundations for the rational development of compounds with anti-HIV activity.
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Affiliation(s)
- Pablo Carravilla
- Biofisika Institute (CSIC, UPV/EHU) & Department of Biochemistry & Molecular Biology, University of the Basque Country (UPV/EHU), PO Box 644, 48080 Bilbao, Spain
| | - José L Nieva
- Biofisika Institute (CSIC, UPV/EHU) & Department of Biochemistry & Molecular Biology, University of the Basque Country (UPV/EHU), PO Box 644, 48080 Bilbao, Spain
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76
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Speerstra S, Chistov AA, Proskurin GV, Aralov AV, Ulashchik EA, Streshnev PP, Shmanai VV, Korshun VA, Schang LM. Antivirals acting on viral envelopes via biophysical mechanisms of action. Antiviral Res 2018; 149:164-173. [DOI: 10.1016/j.antiviral.2017.11.018] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 11/17/2017] [Accepted: 11/20/2017] [Indexed: 01/04/2023]
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77
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Oka T. Small-Angle X-ray Crystallography on Single-Crystal Regions of Inverse Bicontinuous Cubic Phases: Lipid Bilayer Structures and Gaussian Curvature-Dependent Fluctuations. J Phys Chem B 2017; 121:11399-11409. [PMID: 29172522 DOI: 10.1021/acs.jpcb.7b08589] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
I report for the first time an X-ray crystallographic study on single-crystal regions of cubic phases of a lyotropic liquid crystal. The single-crystal regions of three inverse bicontinuous cubic phases of a lipid, monoolein, diffracted X-ray only in small-angle regions, but amplitudes of structure factors were determined from the small-angle X-ray diffraction data with high accuracy. Structure factors from lipid bilayer models with constant thickness were optimized to amplitudes obtained from the X-ray data. By using amplitudes of the structure factors from X-ray data and phases from the models, electron density maps of three cubic phases were reconstructed. Lipid bilayer membranes, consisting of high density head regions and low density tail regions, were clearly distinguished in the electron density maps. Water regions had slightly lower density than that of the lipid head regions and were clearly visible for two of the cubic phases. Centers of bilayer membranes were located on the corresponding triply periodic minimal surfaces in the maps. Electron density data indicated Gaussian curvature-dependent fluctuations of bilayer membranes: the smaller the Gaussian curvature is, the larger the fluctuation becomes. The technique described in this report is expected to bring new knowledge in the structural research of lyotropic liquid crystals.
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Affiliation(s)
- Toshihiko Oka
- Department of Physics, Faculty of Science, and ‡Nanomaterials Research Division, Research Institute of Electronics, Shizuoka University , Shizuoka 422-8529, Japan
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78
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Boonstra S, Onck PR, van der Giessen E. Computation of Hemagglutinin Free Energy Difference by the Confinement Method. J Phys Chem B 2017; 121:11292-11303. [PMID: 29151344 PMCID: PMC5742479 DOI: 10.1021/acs.jpcb.7b09699] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 11/15/2017] [Indexed: 11/28/2022]
Abstract
Hemagglutinin (HA) mediates membrane fusion, a crucial step during influenza virus cell entry. How many HAs are needed for this process is still subject to debate. To aid in this discussion, the confinement free energy method was used to calculate the conformational free energy difference between the extended intermediate and postfusion state of HA. Special care was taken to comply with the general guidelines for free energy calculations, thereby obtaining convergence and demonstrating reliability of the results. The energy that one HA trimer contributes to fusion was found to be 34.2 ± 3.4kBT, similar to the known contributions from other fusion proteins. Although computationally expensive, the technique used is a promising tool for the further energetic characterization of fusion protein mechanisms. Knowledge of the energetic contributions per protein, and of conserved residues that are crucial for fusion, aids in the development of fusion inhibitors for antiviral drugs.
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Affiliation(s)
- Sander Boonstra
- Micromechanics of Materials,
Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Patrick R. Onck
- Micromechanics of Materials,
Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Erik van der Giessen
- Micromechanics of Materials,
Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
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79
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Switching between Successful and Dead-End Intermediates in Membrane Fusion. Int J Mol Sci 2017; 18:ijms18122598. [PMID: 29207481 PMCID: PMC5751201 DOI: 10.3390/ijms18122598] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 11/21/2017] [Accepted: 12/01/2017] [Indexed: 11/16/2022] Open
Abstract
Fusion of cellular membranes during normal biological processes, including proliferation, or synaptic transmission, is mediated and controlled by sophisticated protein machinery ensuring the preservation of the vital barrier function of the membrane throughout the process. Fusion of virus particles with host cell membranes is more sparingly arranged and often mediated by a single fusion protein, and the virus can afford to be less discriminative towards the possible different outcomes of fusion attempts. Formation of leaky intermediates was recently observed in some fusion processes, and an alternative trajectory of the process involving formation of π-shaped structures was suggested. In this study, we apply the methods of elasticity theory and Lagrangian formalism augmented by phenomenological and molecular geometry constraints and boundary conditions to investigate the traits of this trajectory and the drivers behind the choice of one of the possible scenarios depending on the properties of the system. The alternative pathway proved to be a dead end, and, depending on the parameters of the participating membranes and fusion proteins, the system can either reversibly enter the corresponding “leaky” configuration or be trapped in it. A parametric study in the biologically relevant range of variables emphasized the fusion protein properties crucial for the choice of the fusion scenario.
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80
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Xu Y, Kuhlmann J, Brennich M, Komorowski K, Jahn R, Steinem C, Salditt T. Reconstitution of SNARE proteins into solid-supported lipid bilayer stacks and X-ray structure analysis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:566-578. [PMID: 29106973 DOI: 10.1016/j.bbamem.2017.10.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 10/01/2017] [Accepted: 10/24/2017] [Indexed: 11/26/2022]
Abstract
SNAREs are known as an important family of proteins mediating vesicle fusion. For various biophysical studies, they have been reconstituted into supported single bilayers via proteoliposome adsorption and rupture. In this study we extended this method to the reconstitution of SNAREs into supported multilamellar lipid membranes, i.e. oriented multibilayer stacks, as an ideal model system for X-ray structure analysis (X-ray reflectivity and diffraction). The reconstitution was implemented through a pathway of proteomicelle, proteoliposome and multibilayer. To monitor the structural evolution in each step, we used small-angle X-ray scattering for the proteomicelles and proteoliposomes, followed by X-ray reflectivity and grazing-incidence small-angle scattering for the multibilayers. Results show that SNAREs can be successfully reconstituted into supported multibilayers, with high enough orientational alignment for the application of surface sensitive X-ray characterizations. Based on this protocol, we then investigated the effect of SNAREs on the structure and phase diagram of the lipid membranes. Beyond this application, this reconstitution protocol could also be useful for X-ray analysis of many further membrane proteins.
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Affiliation(s)
- Yihui Xu
- Institut für Röntgenphysik, Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Jan Kuhlmann
- Institut für Organische und Biomolekulare Chemie, Universität Göttingen, Tammannstraße 2, Göttingen 37077, Germany
| | - Martha Brennich
- Structural Biology Group, European Synchrotron Radiation Facility, 71 Avenue des Martyrs, CS 90181, Grenoble 38042, France
| | - Karlo Komorowski
- Institut für Röntgenphysik, Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max-Planck Institute for Biophysical Chemistry, Am Faßberg 11, Göttingen 37077, Germany
| | - Claudia Steinem
- Institut für Organische und Biomolekulare Chemie, Universität Göttingen, Tammannstraße 2, Göttingen 37077, Germany
| | - Tim Salditt
- Institut für Röntgenphysik, Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
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81
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Khondker A, Alsop RJ, Dhaliwal A, Saem S, Moran-Mirabal JM, Rheinstädter MC. Membrane Cholesterol Reduces Polymyxin B Nephrotoxicity in Renal Membrane Analogs. Biophys J 2017; 113:2016-2028. [PMID: 29117525 DOI: 10.1016/j.bpj.2017.09.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2017] [Revised: 08/17/2017] [Accepted: 09/13/2017] [Indexed: 01/21/2023] Open
Abstract
Polymyxin B (PmB) is a "last-line" antibiotic scarcely used due to its nephrotoxicity. However, the molecular basis for antibiotic nephrotoxicity is not clearly understood. We prepared kidney membrane analogs of detergent-susceptible membranes, depleted of cholesterol, and cholesterol enriched, resistant membranes. In both analogs, PmB led to membrane damage. By combining x-ray diffraction, molecular dynamics simulations, and electrochemistry, we present evidence for two populations of PmB molecules: peptides that lie flat on the membranes, and an inserted state. In cholesterol depleted membranes, PmB forms clusters on the membranes leading to an indentation of the bilayers and increase in water permeation. The inserted peptides formed aggregates in the membrane core leading to further structural instabilities and increased water intake. The presence of cholesterol in the resistant membrane analogs led to a significant decrease in membrane damage. Although cholesterol did not inhibit peptide insertion, it minimized peptide clustering and water intake through stabilization of the bilayer structure and suppression of lipid and peptide mobility.
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Affiliation(s)
- Adree Khondker
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
| | - Richard J Alsop
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
| | - Alexander Dhaliwal
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
| | - Sokunthearath Saem
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Ontario, Canada
| | - Jose M Moran-Mirabal
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Ontario, Canada
| | - Maikel C Rheinstädter
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada.
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82
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Hastoy B, Clark A, Rorsman P, Lang J. Fusion pore in exocytosis: More than an exit gate? A β-cell perspective. Cell Calcium 2017; 68:45-61. [PMID: 29129207 DOI: 10.1016/j.ceca.2017.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 10/17/2017] [Accepted: 10/24/2017] [Indexed: 12/14/2022]
Abstract
Secretory vesicle exocytosis is a fundamental biological event and the process by which hormones (like insulin) are released into the blood. Considerable progress has been made in understanding this precisely orchestrated sequence of events from secretory vesicle docked at the cell membrane, hemifusion, to the opening of a membrane fusion pore. The exact biophysical and physiological regulation of these events implies a close interaction between membrane proteins and lipids in a confined space and constrained geometry to ensure appropriate delivery of cargo. We consider some of the still open questions such as the nature of the initiation of the fusion pore, the structure and the role of the Soluble N-ethylmaleimide-sensitive-factor Attachment protein REceptor (SNARE) transmembrane domains and their influence on the dynamics and regulation of exocytosis. We discuss how the membrane composition and protein-lipid interactions influence the likelihood of the nascent fusion pore forming. We relate these factors to the hypothesis that fusion pore expansion could be affected in type-2 diabetes via changes in disease-related gene transcription and alterations in the circulating lipid profile. Detailed characterisation of the dynamics of the fusion pore in vitro will contribute to understanding the larger issue of insulin secretory defects in diabetes.
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Affiliation(s)
- Benoit Hastoy
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK.
| | - Anne Clark
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK; Metabolic Research, Institute of Neuroscience and Physiology, University of Goteborg, Medicinaregatan 11, S-41309 Göteborg, Sweden
| | - Jochen Lang
- Laboratoire de Chimie et Biologie des Membranes et Nano-objets (CBMN), CNRS UMR 5248, Université de Bordeaux, Allée de Geoffrey St Hilaire, 33600 Pessac, France.
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83
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Zhong Q, Melchior L, Peng J, Huang Q, Wang Z, Salditt T. Goos-Hänchen effect observed for focused x-ray beams under resonant mode excitation. OPTICS EXPRESS 2017; 25:17431-17445. [PMID: 28789235 DOI: 10.1364/oe.25.017431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 06/21/2017] [Indexed: 06/07/2023]
Abstract
We have coupled a nano-focused synchrotron beam into a planar x-ray waveguide structure through a thinned cladding, using the resonant beam coupling (RBC) geometry, which is well established for coupling of macroscopic x-ray beams into x-ray waveguides. By reducing the beam size and using specially designed waveguide structures with multiple guiding layers, we can observe two reflected beams of similar amplitudes upon resonant mode excitation. At the same time, the second reflected beam is shifted along the surface by several millimeters, constituting a exceptionally large Goos-Hänchen effect. We evidence this effect based on its characteristic far-field patterns resulting from interference of the multiple reflected beams. The experimental results are in perfect agreement with finite-difference simulations.
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84
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Bhattacharya G, Giri RP, Saxena H, Agrawal VV, Gupta A, Mukhopadhyay MK, Ghosh SK. X-ray Reflectivity Study of the Interaction of an Imidazolium-Based Ionic Liquid with a Soft Supported Lipid Membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:1295-1304. [PMID: 28092704 DOI: 10.1021/acs.langmuir.6b03192] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Ionic liquids (ILs) are important for their antimicrobial activity and are found to be toxic to some microorganisms. To shed light on the mechanism of their activities, the interaction of an imidazolium-based IL 1-butyl-3-methylimidazolium tetrfluoroborate ([BMIM][BF4]) with E. coli bacteria and cell-membrane-mimicking lipid mono- and bilayers has been studied. The survival of the bacteria and corresponding growth inhibition are observed to be functions of the concentration of the IL. The IL alters the pressure-area isotherm of the monolayer formed at an air-water interface by the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid. The in-plane elasticity of the lipid layer is reduced as a consequence of the insertion of this IL. The X-ray reflectivity study from a polymer-supported lipid bilayer shows strong perturbation in the self-assembled structure of the bilayer due to the interaction. As a consequence, there is a considerable decrease in bilayer thickness and a corresponding increase in electron density. These results, however, depend on the chain configurations of the lipid molecules.
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Affiliation(s)
| | - R P Giri
- Saha Institute of Nuclear Physics, Bidhannagar, Kolkata 700064, India
| | | | - V V Agrawal
- National Physical Laboratory, Dr. K S Krishnan Marg, New Delhi 110012, India
| | | | - M K Mukhopadhyay
- Saha Institute of Nuclear Physics, Bidhannagar, Kolkata 700064, India
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85
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Narayanan T, Wacklin H, Konovalov O, Lund R. Recent applications of synchrotron radiation and neutrons in the study of soft matter. CRYSTALLOGR REV 2017. [DOI: 10.1080/0889311x.2016.1277212] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
| | - Hanna Wacklin
- European Spallation Source ERIC, Lund, Sweden
- Physical Chemistry, Lund University, Lund, Sweden
| | | | - Reidar Lund
- Department of Chemistry, University of Oslo, Blindern, Oslo, Norway
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86
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Han J, Pluhackova K, Böckmann RA. The Multifaceted Role of SNARE Proteins in Membrane Fusion. Front Physiol 2017; 8:5. [PMID: 28163686 PMCID: PMC5247469 DOI: 10.3389/fphys.2017.00005] [Citation(s) in RCA: 178] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Accepted: 01/04/2017] [Indexed: 12/28/2022] Open
Abstract
Membrane fusion is a key process in all living organisms that contributes to a variety of biological processes including viral infection, cell fertilization, as well as intracellular transport, and neurotransmitter release. In particular, the various membrane-enclosed compartments in eukaryotic cells need to exchange their contents and communicate across membranes. Efficient and controllable fusion of biological membranes is known to be driven by cooperative action of SNARE proteins, which constitute the central components of the eukaryotic fusion machinery responsible for fusion of synaptic vesicles with the plasma membrane. During exocytosis, vesicle-associated v-SNARE (synaptobrevin) and target cell-associated t-SNAREs (syntaxin and SNAP-25) assemble into a core trans-SNARE complex. This complex plays a versatile role at various stages of exocytosis ranging from the priming to fusion pore formation and expansion, finally resulting in the release or exchange of the vesicle content. This review summarizes current knowledge on the intricate molecular mechanisms underlying exocytosis triggered and catalyzed by SNARE proteins. Particular attention is given to the function of the peptidic SNARE membrane anchors and the role of SNARE-lipid interactions in fusion. Moreover, the regulatory mechanisms by synaptic auxiliary proteins in SNARE-driven membrane fusion are briefly outlined.
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Affiliation(s)
- Jing Han
- Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Xi'an Jiaotong University Health Science CenterXi'an, China; Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-NürnbergErlangen, Germany
| | - Kristyna Pluhackova
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
| | - Rainer A Böckmann
- Computational Biology, Department of Biology, Friedrich-Alexander Universität Erlangen-Nürnberg Erlangen, Germany
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87
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X-ray structural investigations of fusion intermediates: Lipid model systems and beyond. Semin Cell Dev Biol 2016; 60:65-77. [DOI: 10.1016/j.semcdb.2016.06.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 06/15/2016] [Accepted: 06/20/2016] [Indexed: 11/20/2022]
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88
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SNARE-mediated membrane fusion trajectories derived from force-clamp experiments. Proc Natl Acad Sci U S A 2016; 113:13051-13056. [PMID: 27807132 DOI: 10.1073/pnas.1615885113] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Fusion of lipid bilayers is usually prevented by large energy barriers arising from removal of the hydration shell, formation of highly curved structures, and, eventually, fusion pore widening. Here, we measured the force-dependent lifetime of fusion intermediates using membrane-coated silica spheres attached to cantilevers of an atomic-force microscope. Analysis of time traces obtained from force-clamp experiments allowed us to unequivocally assign steps in deflection of the cantilever to membrane states during the SNARE-mediated fusion with solid-supported lipid bilayers. Force-dependent lifetime distributions of the various intermediate fusion states allowed us to propose the likelihood of different fusion pathways and to assess the main free energy barrier, which was found to be related to passing of the hydration barrier and splaying of lipids to eventually enter either the fully fused state or a long-lived hemifusion intermediate. The results were compared with SNARE mutants that arrest adjacent bilayers in the docked state and membranes in the absence of SNAREs but presence of PEG or calcium. Only with the WT SNARE construct was appreciable merging of both bilayers observed.
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89
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Kawamoto S, Klein ML, Shinoda W. Coarse-grained molecular dynamics study of membrane fusion: Curvature effects on free energy barriers along the stalk mechanism. J Chem Phys 2016; 143:243112. [PMID: 26723597 DOI: 10.1063/1.4933087] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The effects of membrane curvature on the free energy barrier for membrane fusion have been investigated using coarse-grained molecular dynamics (CG-MD) simulations, assuming that fusion takes place through a stalk intermediate. Free energy barriers were estimated for stalk formation as well as for fusion pore formation using the guiding potential method. Specifically, the three different geometries of two apposed membranes were considered: vesicle-vesicle, vesicle-planar, and planar-planar membranes. The free energy barriers for the resulting fusion were found to depend importantly on the fusing membrane geometries; the lowest barrier was obtained for vesicular membranes. Further, lipid sorting was observed in fusion of the mixed membranes of dimyristoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine (DOPE). Specifically, DOPE molecules were found to assemble around the stalk to support the highly negative curved membrane surface. A consistent result for lipid sorting was observed when a simple continuum model (CM) was used, where the Helfrich energy and mixing entropy of the lipids were taken into account. However, the CM predicts a much higher free energy barrier than found using CG-MD. This discrepancy originates from the conformational changes of lipids, which were not considered in the CM. The results of the CG-MD simulations reveal that a large conformational change in the lipid takes place around the stalk region, which results in a reduction of free energy barriers along the stalk mechanism of membrane fusion.
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Affiliation(s)
- Shuhei Kawamoto
- Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan
| | - Michael L Klein
- Institute for Computational Molecular Science, Temple University, SERC Building 1925 North 12th Street, Philadelphia, Pennsylvania 19122, USA
| | - Wataru Shinoda
- Department of Applied Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan
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90
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Sodt A, Venable R, Lyman E, Pastor R. Nonadditive Compositional Curvature Energetics of Lipid Bilayers. PHYSICAL REVIEW LETTERS 2016; 117:138104. [PMID: 27715135 PMCID: PMC5134905 DOI: 10.1103/physrevlett.117.138104] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Indexed: 05/26/2023]
Abstract
The unique properties of the individual lipids that compose biological membranes together determine the energetics of the surface. The energetics of the surface, in turn, govern the formation of membrane structures and membrane reshaping processes, and thus they will underlie cellular-scale models of viral fusion, vesicle-dependent transport, and lateral organization relevant to signaling. The spontaneous curvature, to the best of our knowledge, is always assumed to be additive. We describe observations from simulations of unexpected nonadditive compositional curvature energetics of two lipids essential to the plasma membrane: sphingomyelin and cholesterol. A model is developed that connects molecular interactions to curvature stress, and which explains the role of local composition. Cholesterol is shown to lower the number of effective Kuhn segments of saturated acyl chains, reducing lateral pressure below the neutral surface of bending and favoring positive curvature. The effect is not observed for unsaturated (flexible) acyl chains. Likewise, hydrogen bonding between sphingomyelin lipids leads to positive curvature, but only at sufficient concentration, below which the lipid prefers negative curvature.
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Affiliation(s)
- A.J. Sodt
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
| | - R.M. Venable
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
| | - E. Lyman
- Department of Physics and Astronomy; Department of Chemistry and Biochemistry, University of Delaware, Newark, DE
| | - R.W. Pastor
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
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91
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Fan ZA, Tsang KY, Chen SH, Chen YF. Revisit the Correlation between the Elastic Mechanics and Fusion of Lipid Membranes. Sci Rep 2016; 6:31470. [PMID: 27534263 PMCID: PMC4989284 DOI: 10.1038/srep31470] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 07/18/2016] [Indexed: 01/10/2023] Open
Abstract
Membrane fusion is a vital process in key cellular events. The fusion capability of a membrane depends on its elastic properties and varies with its lipid composition. It is believed that as the composition varies, the consequent change in C0 (monolayer spontaneous curvature) is the major factor dictating fusion, owing to the associated variation in GEs (elastic energies) of the fusion intermediates (e.g. stalk). By exploring the correlations among fusion, C0 and Kcp (monolayer bending modulus), we revisit this long-held belief and re-examine the fusogenic contributions of some relevant factors. We observe that not only C0 but also Kcp variations affect fusion, with depression in Kcp leading to suppression in fusion. Variations in GEs and inter-membrane interactions cannot account for the Kcp-fusion correlation; fusion is suppressed even as the GEs decrease with Kcp, indicating the presence of factor(s) with fusogenic importance overtaking that of GE. Furthermore, analyses find that the C0 influence on fusion is effected via modulating GE of the pre-fusion planar membrane, rather than stalk. The results support a recent proposition calling for a paradigm shift from the conventional view of fusion and may reshape our understanding to the roles of fusogenic proteins in regulating cellular fusion machineries.
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Affiliation(s)
- Zih-An Fan
- Department of Chemical and Materials Engineering, National Central University, No. 300, Zhongda Rd., Zhongli District, Taoyuan 32001, Taiwan
| | - Kuan-Yu Tsang
- Department of Chemical and Materials Engineering, National Central University, No. 300, Zhongda Rd., Zhongli District, Taoyuan 32001, Taiwan
| | - Si-Han Chen
- Department of Chemical and Materials Engineering, National Central University, No. 300, Zhongda Rd., Zhongli District, Taoyuan 32001, Taiwan
| | - Yi-Fan Chen
- Department of Chemical and Materials Engineering, National Central University, No. 300, Zhongda Rd., Zhongli District, Taoyuan 32001, Taiwan
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92
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Vadakkan KI. Neurodegenerative disorders share common features of "loss of function" states of a proposed mechanism of nervous system functions. Biomed Pharmacother 2016; 83:412-430. [PMID: 27424323 DOI: 10.1016/j.biopha.2016.06.042] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 06/07/2016] [Accepted: 06/25/2016] [Indexed: 12/11/2022] Open
Abstract
Neurodegenerative disorders are highly heterogeneous for the locations affected and the nature of the aggregated proteins. Nearly 80% of the neurodegenerative disorders occur sporadically, indicating that certain factors must combine to initiate the degenerative changes. The contiguous extension of degenerative changes from cell to cell, the association with viral fusion proteins, loss of dendritic spines (postsynaptic terminals), and the eventual degeneration of cells indicate the presence of a unique mechanism for inter-cellular spread of pathology. It is not known whether the "loss of function" states of the still unknown normal nervous system operations can lead to neurodegenerative disorders. Here, the possible loss of function states of a proposed normal nervous system function are examined. A reversible inter-postsynaptic functional LINK (IPL) mechanism, consisting of transient inter-postsynaptic membrane (IPM) hydration exclusion and partial to complete IPM hemifusions, was proposed as a critical step necessary for the binding process and the induction of internal sensations of higher brain functions. When various findings from different neurodegenerative disorders are systematically organized and examined, disease features match the effects of loss of function states of different IPLs. Changes in membrane composition, enlargement of dendritic spines by dopamine and viral fusion proteins are capable of altering the IPLs to form IPM fusion. The latter can lead to the observed lateral spread of pathology, inter-neuronal cytoplasmic content mixing and abnormal protein aggregation. Since both the normal mechanism of reversible IPM hydration exclusion and the pathological process of transient IPM fusion can evade detection, testing their occurrence may provide preventive and therapeutic opportunities for these disorders.
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93
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Visualization and Sequencing of Membrane Remodeling Leading to Influenza Virus Fusion. J Virol 2016; 90:6948-6962. [PMID: 27226364 DOI: 10.1128/jvi.00240-16] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2016] [Accepted: 05/14/2016] [Indexed: 12/31/2022] Open
Abstract
UNLABELLED Protein-mediated membrane fusion is an essential step in many fundamental biological events, including enveloped virus infection. The nature of protein and membrane intermediates and the sequence of membrane remodeling during these essential processes remain poorly understood. Here we used cryo-electron tomography (cryo-ET) to image the interplay between influenza virus and vesicles with a range of lipid compositions. By following the population kinetics of membrane fusion intermediates imaged by cryo-ET, we found that membrane remodeling commenced with the hemagglutinin fusion protein spikes grappling onto the target membrane, followed by localized target membrane dimpling as local clusters of hemagglutinin started to undergo conformational refolding. The local dimples then transitioned to extended, tightly apposed contact zones where the two proximal membrane leaflets were in most cases indistinguishable from each other, suggesting significant dehydration and possible intermingling of the lipid head groups. Increasing the content of fusion-enhancing cholesterol or bis-monoacylglycerophosphate in the target membrane led to an increase in extended contact zone formation. Interestingly, hemifused intermediates were found to be extremely rare in the influenza virus fusion system studied here, most likely reflecting the instability of this state and its rapid conversion to postfusion complexes, which increased in population over time. By tracking the populations of fusion complexes over time, the architecture and sequence of membrane reorganization leading to efficient enveloped virus fusion were thus resolved. IMPORTANCE Enveloped viruses employ specialized surface proteins to mediate fusion of cellular and viral membranes that results in the formation of pores through which the viral genetic material is delivered to the cell. For influenza virus, the trimeric hemagglutinin (HA) glycoprotein spike mediates host cell attachment and membrane fusion. While structures of a subset of conformations and parts of the fusion machinery have been characterized, the nature and sequence of membrane deformations during fusion have largely eluded characterization. Building upon studies that focused on early stages of HA-mediated membrane remodeling, here cryo-electron tomography (cryo-ET) was used to image the three-dimensional organization of intact influenza virions at different stages of fusion with liposomes, leading all the way to completion of the fusion reaction. By monitoring the evolution of fusion intermediate populations over the course of acid-induced fusion, we identified the progression of membrane reorganization that leads to efficient fusion by an enveloped virus.
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94
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Rost U, Xu Y, Salditt T, Diederichsen U. Heavy-Atom Labeled Transmembrane β-Peptides: Synthesis, CD-Spectroscopy, and X-ray Diffraction Studies in Model Lipid Multilayer. Chemphyschem 2016; 17:2525-34. [DOI: 10.1002/cphc.201600289] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2016] [Indexed: 11/07/2022]
Affiliation(s)
- Ulrike Rost
- Institute for Organic and Biomolecular Chemistry; Georg-August-University Göttingen; Tammannstr. 2 37077 Göttingen Germany
| | - Yihui Xu
- Institute for X-ray Physics; Georg-August-University Göttingen; Friedrich-Hund-Platz 1 37077 Göttingen Germany
| | - Tim Salditt
- Institute for X-ray Physics; Georg-August-University Göttingen; Friedrich-Hund-Platz 1 37077 Göttingen Germany
| | - Ulf Diederichsen
- Institute for Organic and Biomolecular Chemistry; Georg-August-University Göttingen; Tammannstr. 2 37077 Göttingen Germany
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95
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The role of cholesterol in membrane fusion. Chem Phys Lipids 2016; 199:136-143. [PMID: 27179407 DOI: 10.1016/j.chemphyslip.2016.05.003] [Citation(s) in RCA: 243] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Revised: 05/07/2016] [Accepted: 05/10/2016] [Indexed: 12/21/2022]
Abstract
Cholesterol modulates the bilayer structure of biological membranes in multiple ways. It changes the fluidity, thickness, compressibility, water penetration and intrinsic curvature of lipid bilayers. In multi-component lipid mixtures, cholesterol induces phase separations, partitions selectively between different coexisting lipid phases, and causes integral membrane proteins to respond by changing conformation or redistribution in the membrane. But, which of these often overlapping properties are important for membrane fusion?-Here we review a range of recent experiments that elucidate the multiple roles that cholesterol plays in SNARE-mediated and viral envelope glycoprotein-mediated membrane fusion.
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96
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High cholesterol obviates a prolonged hemifusion intermediate in fast SNARE-mediated membrane fusion. Biophys J 2016. [PMID: 26200867 DOI: 10.1016/j.bpj.2015.06.022] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Cholesterol is essential for exocytosis in secretory cells, but the exact molecular mechanism by which it facilitates exocytosis is largely unknown. Distinguishing contributions from the lateral organization and dynamics of membrane proteins to vesicle docking and fusion and the promotion of fusion pores by negative intrinsic spontaneous curvature and other mechanical effects of cholesterol have been elusive. To shed more light on this process, we examined the effect of cholesterol on SNARE-mediated membrane fusion in a single-vesicle assay that is capable of resolving docking and elementary steps of fusion with millisecond time resolution. The effect of cholesterol on fusion pore formation between synaptobrevin-2 (VAMP-2)-containing proteoliposomes and acceptor t-SNARE complex-containing planar supported bilayers was examined using both membrane and content fluorescent markers. This approach revealed that increasing cholesterol in either the t-SNARE or the v-SNARE membrane favors a mechanism of direct fusion pore opening, whereas low cholesterol favors a mechanism leading to a long-lived (>5 s) hemifusion state. The amount of cholesterol in the target membrane had no significant effect on docking of synaptobrevin vesicles. Comparative studies with α-tocopherol (vitamin E) show that the negative intrinsic spontaneous curvature of cholesterol and its presumed promotion of a very short-lived (<50 ms) lipid stalk intermediate is the main factor that favors rapid fusion pore opening at high cholesterol. This study also shows that this single-vesicle fusion assay can distinguish between hemifusion and full fusion with only a single lipid dye, thereby freeing up a fluorescence channel for the simultaneous measurement of another parameter in fast time-resolved fusion assays.
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97
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Keidel A, Bartsch TF, Florin EL. Direct observation of intermediate states in model membrane fusion. Sci Rep 2016; 6:23691. [PMID: 27029285 PMCID: PMC4814778 DOI: 10.1038/srep23691] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Accepted: 03/09/2016] [Indexed: 12/28/2022] Open
Abstract
We introduce a novel assay for membrane fusion of solid supported membranes on silica beads and on coverslips. Fusion of the lipid bilayers is induced by bringing an optically trapped bead in contact with the coverslip surface while observing the bead's thermal motion with microsecond temporal and nanometer spatial resolution using a three-dimensional position detector. The probability of fusion is controlled by the membrane tension on the particle. We show that the progression of fusion can be monitored by changes in the three-dimensional position histograms of the bead and in its rate of diffusion. We were able to observe all fusion intermediates including transient fusion, formation of a stalk, hemifusion and the completion of a fusion pore. Fusion intermediates are characterized by axial but not lateral confinement of the motion of the bead and independently by the change of its rate of diffusion due to the additional drag from the stalk-like connection between the two membranes. The detailed information provided by this assay makes it ideally suited for studies of early events in pure lipid bilayer fusion or fusion assisted by fusogenic molecules.
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Affiliation(s)
- Andrea Keidel
- Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
| | - Tobias F. Bartsch
- Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York, 10065, USA
| | - Ernst-Ludwig Florin
- Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
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98
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Ryham RJ, Klotz TS, Yao L, Cohen FS. Calculating Transition Energy Barriers and Characterizing Activation States for Steps of Fusion. Biophys J 2016; 110:1110-24. [PMID: 26958888 PMCID: PMC4788739 DOI: 10.1016/j.bpj.2016.01.013] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Revised: 01/05/2016] [Accepted: 01/13/2016] [Indexed: 12/29/2022] Open
Abstract
We use continuum mechanics to calculate an entire least energy pathway of membrane fusion, from stalk formation, to pore creation, and through fusion pore enlargement. The model assumes that each structure in the pathway is axially symmetric. The static continuum stalk structure agrees quantitatively with experimental stalk architecture. Calculations show that in a stalk, the distal monolayer is stretched and the stored stretching energy is significantly less than the tilt energy of an unstretched distal monolayer. The string method is used to determine the energy of the transition barriers that separate intermediate states and the dynamics of two bilayers as they pass through them. Hemifusion requires a small amount of energy independently of lipid composition, while direct transition from a stalk to a fusion pore without a hemifusion intermediate is highly improbable. Hemifusion diaphragm expansion is spontaneous for distal monolayers containing at least two lipid components, given sufficiently negative diaphragm spontaneous curvature. Conversely, diaphragms formed from single-component distal monolayers do not expand without the continual injection of energy. We identify a diaphragm radius, below which central pore expansion is spontaneous. For larger diaphragms, prior studies have shown that pore expansion is not axisymmetric, and here our calculations supply an upper bound for the energy of the barrier against pore formation. The major energy-requiring deformations in the steps of fusion are: widening of a hydrophobic fissure in bilayers for stalk formation, splay within the expanding hemifusion diaphragm, and fissure widening initiating pore formation in a hemifusion diaphragm.
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Affiliation(s)
- Rolf J Ryham
- Department of Mathematics, Fordham University, Bronx, New York.
| | - Thomas S Klotz
- Department of Computational and Applied Mathematics, Rice University, Houston, Texas
| | - Lihan Yao
- Department of Mathematics, Fordham University, Bronx, New York
| | - Fredric S Cohen
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, Illinois
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99
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Fortoul N, Singh P, Hui CY, Bykhovskaia M, Jagota A. Coarse-Grained Model of SNARE-Mediated Docking. Biophys J 2016; 108:2258-69. [PMID: 25954883 DOI: 10.1016/j.bpj.2015.03.053] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 03/24/2015] [Accepted: 03/24/2015] [Indexed: 12/11/2022] Open
Abstract
Synaptic transmission requires that vesicles filled with neurotransmitter molecules be docked to the plasma membrane by the SNARE protein complex. The SNARE complex applies attractive forces to overcome the long-range repulsion between the vesicle and membrane. To understand how the balance between the attractive and repulsive forces defines the equilibrium docked state we have developed a model that combines the mechanics of vesicle/membrane deformation with an apparently new coarse-grained model of the SNARE complex. The coarse-grained model of the SNARE complex is calibrated by comparison with all-atom molecular dynamics simulations as well as by force measurements in laser tweezer experiments. The model for vesicle/membrane interactions includes the forces produced by membrane deformation and hydration or electrostatic repulsion. Combining these two parts, the coarse-grained model of the SNARE complex with membrane mechanics, we study how the equilibrium docked state varies with the number of SNARE complexes. We find that a single SNARE complex is able to bring a typical synaptic vesicle to within a distance of ∼ 3 nm from the membrane. Further addition of SNARE complexes shortens this distance, but an overdocked state of >4-6 SNAREs actually increases the equilibrium distance.
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Affiliation(s)
- Nicole Fortoul
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania
| | - Pankaj Singh
- Department of Mechanical & Aerospace Engineering, Cornell University, Ithaca, New York
| | - Chung-Yuen Hui
- Department of Mechanical & Aerospace Engineering, Cornell University, Ithaca, New York
| | - Maria Bykhovskaia
- Neuroscience Department, Universidad Central del Caribe, Bayamon, Puerto Rico
| | - Anand Jagota
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania; Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania.
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100
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Tahir MA, Van Lehn RC, Choi SH, Alexander-Katz A. Solvent-exposed lipid tail protrusions depend on lipid membrane composition and curvature. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1207-15. [PMID: 26828121 DOI: 10.1016/j.bbamem.2016.01.026] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Revised: 01/20/2016] [Accepted: 01/27/2016] [Indexed: 10/22/2022]
Abstract
The stochastic protrusion of hydrophobic lipid tails into solution, a subclass of hydrophobic membrane defects, has recently been shown to be a critical step in a number of biological processes like membrane fusion. Understanding the factors that govern the appearance of lipid tail protrusions is critical for identifying membrane features that affect the rate of fusion or other processes that depend on contact with solvent-exposed lipid tails. In this work, we utilize atomistic molecular dynamics simulations to characterize the likelihood of tail protrusions in phosphotidylcholine lipid bilayers of varying composition, curvature, and hydration. We distinguish two protrusion modes corresponding to atoms near the end of the lipid tail or near the glycerol group. Through potential of mean force calculations, we demonstrate that the thermodynamic cost for inducing a protrusion depends on tail saturation but is insensitive to other bilayer structural properties or hydration above a threshold value. Similarly, highly curved vesicles or micelles increase both the overall frequency of lipid tail protrusions as well as the preference for splay protrusions, both of which play an important role in driving membrane fusion. In multi-component bilayers, however, the incidence of protrusion events does not clearly depend on the mismatch between tail length or tail saturation of the constituent lipids. Together, these results provide significant physical insight into how system components might affect the appearance of protrusions in biological membranes, and help explain the roles of composition or curvature-modifying proteins in membrane fusion.
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Affiliation(s)
- Mukarram A Tahir
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Reid C Van Lehn
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - S H Choi
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Alfredo Alexander-Katz
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
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