INTERACTION OF FUSOGENIC SYNTHETIC PEPTIDE WITH PHOSPHOLIPID-BILAYERS- ORIENTATION OF THE PEPTIDE ALPHA-HELIX AND BINDING ISOTHERM

We studied the binding characteristics of a synthetic 20-residue pepti de to supported single planar bilayers of phosphatidylcholine, and the orientation of the peptide by Fourier-transform infrared spectroscopy with an attenuated total reflection method. This peptide, designed to resemble a putative fusion peptide of influenza virus hemagglutinin, assumes an amphiphilic alpha-helix and induces fusion of Liposomes in an acidic solution (pH similar to 5). At neutral pH, the peptides were bound to lipid bilayers in the manner of a Langmuir's adsorption isot herm, and their orientation was nearly random or oblique. On the other hand, at acidic pH, the peptides were bound, making their helix axis parallel to the membrane surface, and the binding was cooperative. Thi s cooperativity suggested dimerization of the peptides. These characte ristics are expected to be important for the synthetic fusogenic pepti de or the fusion peptide in hemagglutinin to induce membrane fusion.