title: The 1-127 HA2 construct of influenza virus hemagglutinin induces cell-cell hemifusion.
abstract: Conformational changes in the HA2 subunit of influenza hemagglutinin (HA) are coupled to membrane fusion. We investigated the fusogenic activity of the polypeptide FHA2 representing 127 amino-terminal residues of the ectodomain of HA2. While the conformation of FHA2 both at neutral and at low pH is nearly identical to the final low-pH conformation of HA2, FHA2 still induces lipid mixing between liposomes in a low-pH-dependent manner. Here, we found that FHA2 induces lipid mixing between bound cells, indicating that the "spring-loaded" energy is not required for FHA2-mediated membrane merger. Although, unlike HA, FHA2 did not form an expanding fusion pore, both acidic pH and membrane concentrations of FHA2, required for lipid mixing, have been close to those required for HA-mediated fusion. Similar to what is observed for HA, FHA2-induced lipid mixing was reversibly blocked by lysophosphatidylcholine and low temperature, 4 degrees C. The same genetic modification of the fusion peptide inhibits both HA- and FHA2-fusogenic activities. The kink region of FHA2, critical for FHA2-mediated lipid mixing, was exposed in the low-pH conformation of the whole HA prior to fusion. The ability of FHA2 to mediate lipid mixing very similar to HA-mediated lipid mixing is consistent with the hypothesis that hemifusion requires just a portion of the energy released in the conformational change of HA at acidic pH.
authors.affiliation: Section on Membrane Biology, LCMB, NICHD, National Institutes of Health, Building 10, Room 10D04, 10 Center Drive, Bethesda, Maryland 20892-1855, USA.
authors.forename: E
authors.initials: E
authors.lastname: Leikina
authors.forename: D L
authors.initials: DL
authors.lastname: LeDuc
authors.forename: J C
authors.initials: JC
authors.lastname: Macosko
authors.forename: R
authors.initials: R
authors.lastname: Epand
authors.forename: R
authors.initials: R
authors.lastname: Epand
authors.forename: Y K
authors.initials: YK
authors.lastname: Shin
authors.forename: L V
authors.initials: LV
authors.lastname: Chernomordik
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D002448:Cell Adhesion / Q000235:genetics; D002450:Cell Communication / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology / Q000821:virology; D004903:Erythrocyte Aggregation / Q000235:genetics; D004912:Erythrocytes / Q000502:physiology; D005822:Genetic Vectors / Q000502:physiology; D015726:Giant Cells / Q000502:physiology; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D006801:Humans; D050356:Lipid Metabolism; D008055:Lipids / Q000037:antagonists & inhibitors; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D008561:Membrane Fusion / Q000187:drug effects / Q000235:genetics*; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D010641:Phenotype; D017433:Protein Structure, Secondary / Q000235:genetics; D014760:Viral Fusion Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology
chemical_list: D000998:Antiviral Agents; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D008055:Lipids; D008244:Lysophosphatidylcholines; D010446:Peptide Fragments; D014760:Viral Fusion Proteins; C411888:influenza virus hemagglutinin peptide 2 (1-25)