title: Fusion activity of influenza virus PR8/34 correlates with a temperature-induced conformational change within the hemagglutinin ectodomain detected by photochemical labeling.
abstract: Fusion of influenza viruses with membranes is catalyzed by the viral spike protein hemagglutinin (HA). Under mildly acidic conditions (approximately pH 5) this protein undergoes a conformational change that triggers the exposure of the "fusion peptide", the hydrophobic N-terminal segment of the HA2 polypeptide chain. Insertion of this segment into the target membrane (or viral membrane?) is likely to represent a key step along the fusion pathway, but the details are far from being clear. The photoreactive phospholipid 1-palmitoyl-2-[11-[4-[3-(trifluoromethyl)diazirinyl]phenyl] [2-3H]undecanoyl]-sn-glycero-3-phosphocholine ([3H]PTPC/11), inserted into the bilayer of large unilamellar vesicles (LUVs), allowed us to investigate both the interaction of viruses with the vesicles under "prefusion" conditions (pH 5; 0 degrees C) and the fusion process itself occurring at elevated temperatures (greater than 15-20 degrees C) only. Despite the observed binding of viruses to LUVs at pH 5 and 0 degrees C, labeling of HA2 was very weak (less than 0.002% of the radioactivity originally present). In contrast, fusion could be readily monitored by the covalent labeling of that polypeptide chain. We have studied also the effect of temperature on the acid-induced (pH 5) interaction of bromelain-solubilized HA (BHA) with vesicles. Labeling of the BHA2 polypeptide chain was found to show a remarkable correlation with the temperature dependence of the fusion activity of whole viruses. A temperature-induced structural change appears to be critical for both the interaction of BHA with membranes and the expression of fusion activity of intact viruses.
authors.affiliation: Department of Biochemistry, Swiss Federal Institute of Technology, Zürich.
authors.forename: J
authors.initials: J
authors.lastname: Brunner
authors.forename: C
authors.initials: C
authors.lastname: Zugliani
authors.forename: R
authors.initials: R
authors.lastname: Mischler
mesh_terms: D000345:Affinity Labels; D000818:Animals; D002642:Chick Embryo; D004735:Energy Transfer; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D006389:Hemagglutinins, Viral; D009980:Influenza A virus / Q000276:immunology / Q000502:physiology*; D007700:Kinetics; D008081:Liposomes; D008561:Membrane Fusion; D010743:Phospholipids; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014759:Viral Envelope Proteins / Q000378:metabolism*
chemical_list: D000345:Affinity Labels; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D006389:Hemagglutinins, Viral; D008081:Liposomes; D010743:Phospholipids; D014759:Viral Envelope Proteins