Membrane Fusion by Peptide Analogues of Influenza Virus Haemagglutinin

National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, U.K. and 1 Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, Massachusetts 02139, U.S.A. We have studied the interactions of synthetic peptides corresponding to the sequence of the amino terminus of the HA 2 subunit of influenza virus haemagglutinin with artificial lipid membranes. The peptides could fuse cholesterol-free liposomes at neutral as well as acid pH; however, liposomes containing cholesterol could only be fused below pH 6. The fusion process caused leakage of aqueous liposomal contents. Peptides with amino acid substitutions had fusion properties similar to whole haemagglutinin molecules with the corresponding sequence changes. Non-fusogenic peptides still interacted with the membrane but did not cause leakage of liposomal contents. A correlation between the -helical content of peptide and its fusogenicity was noted, but this was not absolute. The results reported here support suggestions for a role of the amino terminus of HA 2 in virus-endosome fusion. Keywords: influenza virus, haemagglutinin, membrane fusion Received 18 January 1988; accepted 20 April 1988.