title: Influenza hemagglutinins outside of the contact zone are necessary for fusion pore expansion.
abstract: Current models for membrane fusion in diverse biological processes are focused on the local action of fusion proteins present in the contact zone where the proteins anchored in one membrane might interact directly with the other membrane. Are the fusion proteins outside of the contact zone just bystanders? Here we assess the role of these "outsider" proteins in influenza virus hemagglutinin-mediated fusion between red blood cells and either hemagglutinin-expressing cells or viral particles. To selectively inhibit or enhance the actions of hemagglutinin outsiders, the antibodies that bind to hemagglutinin and proteases that cleave it were conjugated to polystyrene microspheres too large to enter the contact zone. We also involved hemagglutinin outsiders into interactions with additional red blood cells. We find the hemagglutinin outsiders to be necessary and sufficient for fusion. Interfering with the activity of the hemagglutinin outsiders inhibited fusion. Selective conversion of hemagglutinin outsiders alone into fusion-competent conformation was sufficient to achieve fusion. The discovered functional role of fusion proteins located outside of the contact zone suggests a tempting analogy to mechanisms by which proteins mediate membrane fission from outside of the fission site.
authors.affiliation: Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, NICHD, National Institutes of Health, Bethesda, Maryland 20892-1855, USA.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Leikina
authors.forename: Aditya
authors.initials: A
authors.lastname: Mittal
authors.forename: Myoung-Soon
authors.initials: MS
authors.lastname: Cho
authors.forename: Kamran
authors.initials: K
authors.lastname: Melikov
authors.forename: Michael M
authors.initials: MM
authors.lastname: Kozlov
authors.forename: Leonid V
authors.initials: LV
authors.lastname: Chernomordik
mesh_terms: D001665:Binding Sites; D004912:Erythrocytes / Q000821:virology; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry*; D006801:Humans; D008561:Membrane Fusion; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008863:Microspheres; D008954:Models, Biological; D011137:Polystyrenes / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D013997:Time Factors
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D011137:Polystyrenes