title: Electron cryomicroscopy reveals different F1+F2 protein States in intact parainfluenza virions.
abstract: Electron cryomicrographs of intact parainfluenza virus 5 (PIV5) virions revealed two different surface structures, namely, a continuous layer and distinct individual spikes. The structure of these spikes reconstructed from intact virions was compared with known F ectodomain structures and was found to be different from the prefusion PIV5 F0 structure but, surprisingly, very similar to the human PIV3 F postfusion structure. Hence, we conclude that the individual F1+F2 spikes in intact PIV5 virions also correspond to the postfusion state. Since the observed fusion activity of PIV5 virions has to be associated with prefusion F1+F2 proteins, they have necessarily to be localized in the continuous surface structure. The data therefore strongly suggest that the prefusion state of the F1+F2 protein requires stabilization, most probably by the association with hemagglutinin-neuraminidase. The conversion of F1+F2 proteins from the prefusion toward the postfusion state while embedded in the virus membrane is topologically difficult to comprehend on the basis of established models and demands reconsideration of our current understanding.
authors.affiliation: Forschungszentrum für Elektronenmikroskopie, Freie Universität Berlin, Fabeckstr. 36a, D-14195 Berlin, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Ludwig
authors.forename: Boris
authors.initials: B
authors.lastname: Schade
authors.forename: Christoph
authors.initials: C
authors.lastname: Böttcher
authors.forename: Thomas
authors.initials: T
authors.lastname: Korte
authors.forename: Nina
authors.initials: N
authors.lastname: Ohlwein
authors.forename: Bolormaa
authors.initials: B
authors.lastname: Baljinnyam
authors.forename: Michael
authors.initials: M
authors.lastname: Veit
authors.forename: Andreas
authors.initials: A
authors.lastname: Herrmann
mesh_terms: D000818:Animals; D002417:Cattle; D002459:Cell Fusion; D002460:Cell Line; D002642:Chick Embryo; D020285:Cryoelectron Microscopy; D007091:Image Processing, Computer-Assisted; D010252:Paramyxoviridae / Q000648:ultrastructure*; D017434:Protein Structure, Tertiary; D014764:Viral Proteins / Q000648:ultrastructure*; D014771:Virion / Q000648:ultrastructure*
chemical_list: D014764:Viral Proteins