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J. Virol., 11 1995, 6643-6651, Vol 69, No. 11
DA Steinhauer, SA Wharton, JJ Skehel and DC Wiley
Influenza virus hemagglutinin (HA) fuses membranes at endosomal pH by a
process which involves extrusion of the NH2-terminal region of HA2, the
fusion peptide, from its buried location in the native trimer. We have
examined the amino acid sequence requirements for a functional fusion
peptide by determining the fusion capacities of site-specific mutant HAs
expressed by using vaccinia virus recombinants and of synthetic peptide
analogs of the mutant fusion peptides. The results indicate that for
efficient fusion, alanine can to some extent substitute for the
NH2-terminal glycine of the wild-type fusion peptide but that serine,
histidine, leucine, isoleucine, or phenylalanine cannot. In addition,
mutants containing shorter fusion peptides as a result of single amino acid
deletions are inactive, as is a mutant containing an alanine instead of a
glycine at HA2 residue 8. Substitution of the glycine at HA2 residue 4 with
an alanine increases the pH of fusion, and valine-for-glutamate
substitutions at HA2 residues 11 and 15 are without effect. We confirm
previous reports on the need for specific HAo cleavage to generate
functional HAs, and we show that both inappropriately cleaved HA and mutant
HAs, irrespective of their fusion capacities, upon incubation at low pH
undergo the structural transition required for fusion.
Copyright © 1995, American Society for Microbiology
Studies of the membrane fusion activities of fusion peptide mutants of influenza virus hemagglutinin
Division of Virology, National Institute for Medical Research, London, United Kingdom.
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