title: New insights into the spring-loaded conformational change of influenza virus hemagglutinin.
abstract: Influenza virus hemagglutinin undergoes a conformational change in which a loop-to-helix "spring-loaded" conformational change forms a coiled coil that positions the fusion peptide for interaction with the target bilayer. Previous work has shown that two proline mutations designed to disrupt this change disrupt fusion but did not determine the basis for the fusion defect. In this work, we made six additional mutants with single proline substitutions in the region that undergoes the spring-loaded conformational change and two additional mutants with double proline substitutions in this region. All double mutants were fusion inactive. We analyzed one double mutant, F63P/F70P, as an example. We observed that F63P/F70P undergoes key low-pH-induced conformational changes and binds tightly to target membranes. However, limited proteolysis and electron microscopy observations showed that the mutant forms a coiled coil that is only approximately 50% the length of the wild type, suggesting that it is splayed in its N-terminal half. This work further supports the hypothesis that the spring-loaded conformational change is necessary for fusion. Our data also indicate that the spring-loaded conformational change has another role beyond presenting the fusion peptide to the target membrane.
authors.affiliation: Department of Cell Biology. Department of Microbiology, University of Virginia, Charlottesville, Virginia 22908, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Gruenke
authors.forename: R Todd
authors.initials: RT
authors.lastname: Armstrong
authors.forename: William W
authors.initials: WW
authors.lastname: Newcomb
authors.forename: Jay C
authors.initials: JC
authors.lastname: Brown
authors.forename: Judith M
authors.initials: JM
authors.lastname: White
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002460:Cell Line; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008561:Membrane Fusion; D051379:Mice; D008854:Microscopy, Electron; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D014162:Transfection
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus