title: Influenza-virus membrane fusion by cooperative fold-back of stochastically induced hemagglutinin intermediates.
abstract: Influenza virus penetrates cells by fusion of viral and endosomal membranes catalyzed by the viral hemagglutinin (HA). Structures of the initial and final states of the HA trimer define the fusion endpoints, but do not specify intermediates. We have characterized these transitions by analyzing low-pH-induced fusion kinetics of individual virions and validated the analysis by computer simulation. We detect initial engagement with the target membrane of fusion peptides from independently triggered HAs within the larger virus-target contact patch; fusion then requires engagement of three or four neighboring HA trimers. Effects of mutations in HA indicate that withdrawal of the fusion peptide from a pocket in the pre-fusion trimer is rate-limiting for both events, but the requirement for cooperative action of several HAs to bring the fusing membranes together leads to a long-lived intermediate state for single, extended HA trimers. This intermediate is thus a fundamental aspect of the fusion mechanism. DOI:http://dx.doi.org/10.7554/eLife.00333.001.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology , Harvard Medical School , Boston , United States ; Department of Molecular, Cellular and Developmental Biology , University of Colorado, Boulder , Colorado , United States.
authors.forename: Tijana
authors.initials: T
authors.lastname: Ivanovic
authors.forename: Jason L
authors.initials: JL
authors.lastname: Choi
authors.forename: Sean P
authors.initials: SP
authors.lastname: Whelan
authors.forename: Antoine M
authors.initials: AM
authors.lastname: van Oijen
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Harrison
mesh_terms: D002462:Cell Membrane / Q000378:metabolism* / Q000821:virology; D003198:Computer Simulation; D011992:Endosomes / Q000378:metabolism* / Q000821:virology; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D008954:Models, Biological; D009154:Mutation; D009975:Orthomyxoviridae / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D013269:Stochastic Processes; D014771:Virion; D053586:Virus Internalization
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D008051:Lipid Bilayers; D008567:Membranes, Artificial
keywords: Viruses; enveloped viruses; influenza; lipid bilayer; membrane fusion; single molecule; virus entry
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