Evidence for H +-induced insertion of influenza hemagglutinin HA2 N-terminal segment into viral membrane

Thomas Weber, Günther Paesold, Carmela Galli, Robert Mischler, Giorgio Semenza, Josef Brunner

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Fusion of influenza virus with target membranes is induced by acid and involves complex changes in the viral fusion protein hemagglutinin. At 0 °C, in a first kinetically resolvable step, the hemagglutinin polypeptide 2 (HA2) N-terminal segment (fusion peptide) is exposed and inserts into the target membrane (Tsurudome, M., Glück, R., Graf, R., Falchetto, R., Schaller, U., and Brunner, J. (1992) J. Biol. Chem. 267, 20225-20232). We now report studies of the changes taking place at pH 5.0 and 37 °C, conditions that result in fusion or, in the absence of a target membrane, in inactivation of the virus' fusion capacity. To this end, we synthesized the new photosensitive phospholipid, 1-palmitoyl-2-[decanedioyl mono-[2-( 125I)iodo-4-(3-trifluoromethyl-3H-diazirin-3-yl)-benzyl]ester]-sn- glycero-3-phosphocholine (specific radioactivity, >2000 Ci/mmol), and worked out a protocol to incorporate this lipid into the viral membrane. Subsequent photoactivation of the reagent resulted in selective labeling of the C-terminal portion of the HA2 polypeptide chain, in agreement with the membrane topology of hemagglutinin. When, however, prior to reagent activation, the viruses were exposed at pH 5.0, 37 °C, both the HA2 C-terminal and the N-terminal regions were labeled, suggesting that the HA2 N-terminal segment (fusion peptide) inserted into the viral membrane. Possible implications for fusion and virus inactivation are discussed.

Original languageEnglish
Pages (from-to)18353-18358
Number of pages6
JournalJournal of Biological Chemistry
Issue number28
StatePublished - 15 Jul 1994
Externally publishedYes


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