title: Cryo-electron Microscopy Structures of Chimeric Hemagglutinin Displayed on a Universal Influenza Vaccine Candidate.
abstract: Influenza viruses expressing chimeric hemagglutinins (HAs) are important tools in the quest for a universal vaccine. Using cryo-electron tomography, we have determined the structures of a chimeric HA variant that comprises an H1 stalk and an H5 globular head domain (cH5/1 HA) in native and antibody-bound states. We show that cH5/1 HA is structurally different from native HA, displaying a 60° rotation between the stalk and head groups, leading to a novel and unexpected "open" arrangement of HA trimers. cH5/1N1 viruses also display higher glycoprotein density than pH1N1 or H5N1 viruses, but despite these differences, antibodies that target either the stalk or head domains of hemagglutinins still bind to cH5/1 HA with the same consequences as those observed with native H1 or H5 HA. Our results show that a large range of structural plasticity can be tolerated in the chimeric spike scaffold without disrupting structural and geometric aspects of antibody binding.
  
  
  OBJECTIVE
  Chimeric hemagglutinin proteins are set to undergo human clinical trials as a universal influenza vaccine candidate, yet no structural information for these proteins is available. Using cryo-electron tomography, we report the first three-dimensional (3D) visualization of chimeric hemagglutinin proteins displayed on the surface of the influenza virus. We show that, unexpectedly, the chimeric hemagglutinin structure differs from those of naturally occurring hemagglutinins by displaying a more open head domain and a dramatically twisted head/stalk arrangement. Despite this unusual spatial relationship between head and stalk regions, virus preparations expressing the chimeric hemagglutinin are fully infectious and display a high glycoprotein density, which likely helps induction of a broadly protective immune response.
authors.affiliation: Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Erin E H
authors.initials: EE
authors.lastname: Tran
authors.affiliation: Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Kira A
authors.initials: KA
authors.lastname: Podolsky
authors.affiliation: Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Alberto
authors.initials: A
authors.lastname: Bartesaghi
authors.affiliation: Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Oleg
authors.initials: O
authors.lastname: Kuybeda
authors.affiliation: Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Grandinetti
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
authors.forename: Teddy John
authors.initials: TJ
authors.lastname: Wohlbold
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
authors.forename: Gene S
authors.initials: GS
authors.lastname: Tan
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA Faculty of Life Sciences, University of Vienna, Vienna, Austria.
authors.forename: Raffael
authors.initials: R
authors.lastname: Nachbagauer
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Palese
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
authors.forename: Florian
authors.initials: F
authors.lastname: Krammer
authors.affiliation: Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA ss1@nih.gov.
authors.forename: Sriram
authors.initials: S
authors.lastname: Subramaniam
mesh_terms: D000914:Antibodies, Viral / Q000378:metabolism; D020285:Cryoelectron Microscopy; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics / Q000648:ultrastructure*; D009980:Influenza A virus / Q000235:genetics / Q000648:ultrastructure*; D007252:Influenza Vaccines / Q000235:genetics; D008958:Models, Molecular; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000648:ultrastructure*
chemical_list: D000914:Antibodies, Viral; C543345:H1N1 virus hemagglutinin; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines; D011993:Recombinant Fusion Proteins; C109963:hemagglutinin, avian influenza A virus