title: Molecular requirements for a pandemic influenza virus: An acid-stable hemagglutinin protein.
abstract: Influenza pandemics require that a virus containing a hemagglutinin (HA) surface antigen previously unseen by a majority of the population becomes airborne-transmissible between humans. Although the HA protein is central to the emergence of a pandemic influenza virus, its required molecular properties for sustained transmission between humans are poorly defined. During virus entry, the HA protein binds receptors and is triggered by low pH in the endosome to cause membrane fusion; during egress, HA contributes to virus assembly and morphology. In 2009, a swine influenza virus (pH1N1) jumped to humans and spread globally. Here we link the pandemic potential of pH1N1 to its HA acid stability, or the pH at which this one-time-use nanomachine is either triggered to cause fusion or becomes inactivated in the absence of a target membrane. In surveillance isolates, our data show HA activation pH values decreased during the evolution of H1N1 from precursors in swine (pH 5.5-6.0), to early 2009 human cases (pH 5.5), and then to later human isolates (pH 5.2-5.4). A loss-of-function pH1N1 virus with a destabilizing HA1-Y17H mutation (pH 6.0) was less pathogenic in mice and ferrets, less transmissible by contact, and no longer airborne-transmissible. A ferret-adapted revertant (HA1-H17Y/HA2-R106K) regained airborne transmissibility by stabilizing HA to an activation pH of 5.3, similar to that of human-adapted isolates from late 2009-2014. Overall, these studies reveal that a stable HA (activation pH ≤ 5.5) is necessary for pH1N1 influenza virus pathogenicity and airborne transmissibility in ferrets and is associated with pandemic potential in humans.
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Marion
authors.initials: M
authors.lastname: Russier
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Guohua
authors.initials: G
authors.lastname: Yang
authors.affiliation: Department of Pathology, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Jerold E
authors.initials: JE
authors.lastname: Rehg
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Sook-San
authors.initials: SS
authors.lastname: Wong
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Heba H
authors.initials: HH
authors.lastname: Mostafa
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Thomas P
authors.identifier: http://orcid.org/0000-0002-8960-0728
authors.initials: TP
authors.lastname: Fabrizio
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Subrata
authors.initials: S
authors.lastname: Barman
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105;
authors.forename: Scott
authors.initials: S
authors.lastname: Krauss
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105; Charles.Russell@stjude.org robert.webster@stjude.org.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Webster
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105; Department of Microbiology, Immunology & Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Webby
authors.affiliation: Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN 38105; Department of Microbiology, Immunology & Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163 Charles.Russell@stjude.org robert.webster@stjude.org.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Russell
mesh_terms: D000143:Acids / Q000737:chemistry*; D000818:Animals; D005075:Biological Evolution; D005289:Ferrets / Q000821:virology; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D053118:Influenza A Virus, H1N1 Subtype / Q000472:pathogenicity / Q000502:physiology*; D008297:Male; D008811:Mice, Inbred DBA; D009154:Mutation / Q000235:genetics; D009976:Orthomyxoviridae Infections / Q000473:pathology / Q000635:transmission / Q000821:virology; D058873:Pandemics; D055550:Protein Stability; D013552:Swine; D014775:Virus Activation; D014779:Virus Replication
chemical_list: D000143:Acids; D019267:Hemagglutinin Glycoproteins, Influenza Virus
keywords: fusion glycoprotein; influenza virus; membrane fusion; pandemic; transmission
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