title: The relevance of salt bridges for the stability of the influenza virus hemagglutinin.
abstract: Hemagglutinin (HA) of influenza virus undergoes an irreversible conformational change at acidic pH, mediating viral fusion with the host endosomal membrane. To unravel the molecular basis of the pH-dependent stability of HA, we demonstrate by mutagenesis of the prototype HA of virus strain X31 (H3 subtype) that salt bridges, especially a tetrad salt bridge within the monomers, are crucial for folding and stability of the trimeric ectodomain. This complex (tetrad) salt bridge is highly conserved among influenza virus subtypes. Introducing additional sites of electrostatic attraction between monomers in the distal region enhanced the stability of ectodomain at low pH mimicking the natural variant H2 subtype. We propose that distinct salt bridges in the distal domain may contribute to the enhanced stability of HA of natural virus variants. This hypothesis may provide clues to understanding adaptations of virus strains (for example, avian influenza viruses) in order to preserve stability of the protein in the host-specific environment.
authors.affiliation: Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Institut für Biologie/Biophysik, Invalidenstr. 43, D-10115 Berlin, Germany.
authors.forename: P Sivaramakrishna
authors.initials: PS
authors.lastname: Rachakonda
authors.forename: Michael
authors.initials: M
authors.lastname: Veit
authors.forename: Thomas
authors.initials: T
authors.lastname: Korte
authors.forename: Kai
authors.initials: K
authors.lastname: Ludwig
authors.forename: Christoph
authors.initials: C
authors.lastname: Böttcher
authors.forename: Qiang
authors.initials: Q
authors.lastname: Huang
authors.forename: Michael F G
authors.initials: MF
authors.lastname: Schmidt
authors.forename: Andreas
authors.initials: A
authors.lastname: Herrmann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D011992:Endosomes / Q000378:metabolism; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012492:Salts / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus; D012492:Salts