title: The hemifusion structure induced by influenza virus haemagglutinin is determined by physical properties of the target membranes.
abstract: Influenza A virus haemagglutinin conformational change drives the membrane fusion of viral and endosomal membranes at low pH. Membrane fusion proceeds through an intermediate called hemifusion(1,2). For viral fusion, the hemifusion structures are not determined(3). Here, influenza virus-like particles(4) carrying wild-type haemagglutinin or haemagglutinin hemifusion mutant G1S(5) and liposome mixtures were studied at low pH by Volta phase plate cryo-electron tomography, which improves the signal-to-noise ratio close to focus. We determined two distinct hemifusion structures: a hemifusion diaphragm and a novel structure termed a 'lipidic junction'. Liposomes with lipidic junctions were ruptured with membrane edges stabilized by haemagglutinin. The rupture frequency and hemifusion diaphragm diameter were not affected by G1S mutation, but decreased when the cholesterol level in the liposomes was close to physiological concentrations. We propose that haemagglutinin induces a merger between the viral and target membranes by one of two independent pathways: a rupture-insertion pathway leading to the lipidic junction and a hemifusion-stalk pathway leading to a fusion pore. The latter is relevant under the conditions of influenza virus infection of cells. Cholesterol concentration functions as a pathway switch because of its negative spontaneous curvature in the target bilayer, as determined by continuum analysis.
authors: Section on Integrative Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
authors: Petr
authors: P
authors: Chlanda
authors: Section on Integrative Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
authors: Elena
authors: E
authors: Mekhedov
authors: Section on Integrative Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
authors: Hang
authors: H
authors: Waters
authors: Rocky Mountain Laboratories, Electron Microscopy Unit, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton 59840, Montana, USA.
authors: Cindi L
authors: CL
authors: Schwartz
authors: Rocky Mountain Laboratories, Electron Microscopy Unit, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton 59840, Montana, USA.
authors: Elizabeth R
authors: ER
authors: Fischer
authors: Department of Mathematics, Fordham University, Bronx, New York 10458, USA.
authors: Rolf J
authors: RJ
authors: Ryham
authors: Department of Molecular Biophysics and Physiology, Rush University, Chicago, Illinois 60612, USA.
authors: Fredric S
authors: FS
authors: Cohen
authors: Section on Integrative Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
authors: Paul S
authors: PS
authors: Blank
authors: Section on Integrative Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
authors: Joshua
authors: 0000-0002-1707-3789
authors: J
authors: Zimmerberg
mesh_terms: D002784:Cholesterol / Q000032:analysis; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008561:Membrane Fusion; D008566:Membranes / Q000737:chemistry* / Q000821:virology; D009154:Mutation; D055585:Physical Phenomena; D014760:Viral Fusion Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D008051:Lipid Bilayers; D008081:Liposomes; D014760:Viral Fusion Proteins; C483468:hemagglutinin, human influenza A virus; D002784:Cholesterol