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Membrane fusion by peptide analogues of influenza virus haemagglutinin.

We have studied the interactions of synthetic peptides corresponding to the sequence of the amino terminus of the HA2 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 alpha-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 HA2 in virus-endosome fusion.