title: Linker and/or transmembrane regions of influenza A/Group-1, A/Group-2, and type B virus hemagglutinins are packed differently within trimers.
abstract: Influenza virus hemagglutinin is a homotrimeric spike glycoprotein crucial for virions' attachment, membrane fusion, and assembly reactions. X-ray crystallography data are available for hemagglutinin ectodomains of various types/subtypes but not for anchoring segments. To get structural information for the linker and transmembrane regions of hemagglutinin, influenza A (H1-H16 subtypes except H8 and H15) and B viruses were digested with bromelain or subtilisin Carlsberg, either within virions or in non-ionic detergent micelles. Proteolytical fragments were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Within virions, hemagglutinins of most influenza A/Group-1 and type B virus strains were more susceptible to digestion with bromelain and/or subtilisin compared to A/Group-2 hemagglutinins. The cleavage sites were always located in the hemagglutinin linker sequence. In detergent, 1) bromelain cleaved hemagglutinin of every influenza A subtype in the linker region; 2) subtilisin cleaved Group-2 hemagglutinins in the linker region; 3) subtilisin cleaved Group-1 hemagglutinins in the transmembrane region; 4) both enzymes cleaved influenza B virus hemagglutinin in the transmembrane region. We propose that the A/Group-2 hemagglutinin linker and/or transmembrane regions are more tightly associated within trimers than type A/Group-1 and particularly type B ones. This hypothesis is underpinned by spatial trimeric structure modeling performed for transmembrane regions of both Group-1 and Group-2 hemagglutinin representatives. Differential S-acylation of the hemagglutinin C-terminal anchoring segment with palmitate/stearate residues possibly contributes to fine tuning of transmembrane trimer packing and stabilization since decreased stearate amount correlated with deeper digestion of influenza B and some A/Group-1 hemagglutinins.
authors.affiliation: Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia. kord@belozersky.msu.ru
authors.forename: Larisa V
authors.initials: LV
authors.lastname: Kordyukova
authors.forename: Marina V
authors.initials: MV
authors.lastname: Serebryakova
authors.forename: Anton A
authors.initials: AA
authors.lastname: Polyansky
authors.forename: Ekaterina A
authors.initials: EA
authors.lastname: Kropotkina
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Alexeevski
authors.forename: Michael
authors.initials: M
authors.lastname: Veit
authors.forename: Roman G
authors.initials: RG
authors.lastname: Efremov
authors.forename: Irina Yu
authors.initials: IY
authors.lastname: Filippova
authors.forename: Lyudmila A
authors.initials: LA
authors.lastname: Baratova
mesh_terms: D000595:Amino Acid Sequence; D001704:Biopolymers / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004591:Electrophoresis, Polyacrylamide Gel; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry*; D009980:Influenza A virus / Q000737:chemistry* / Q000254:growth & development; D009981:Influenza B virus / Q000737:chemistry* / Q000254:growth & development; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D001704:Biopolymers; D019267:Hemagglutinin Glycoproteins, Influenza Virus