STRUCTURAL STUDY OF THE RELATIONSHIP BETWEEN THE RATE OF MEMBRANE-FUSION AND THE ABILITY OF THE FUSION PEPTIDE OF INFLUENZA-VIRUS TO PERTURB BILAYERS

The amino-terminal segment of the HA(2) protein of influenza virus (fu sion peptide) has been identified as an important region for membrane fusion. The wild type virus can fuse to membranes more rapidly at pH 5 than at pH 7.4. It has been demonstrated that there is a relationship between the ability of the peptide to promote the formation of invert ed phases and the fusogenicity of the intact virus. In this work, we u se small-angle X-ray diffraction to study the mechanism of the structu ral effect of the peptide, at different pHs, on lipid systems characte rized by each having a different spontaneous radius of curvature, The overall results show that the action of the peptide on the polymorphis m of the lipid systems investigated is strongly pH-dependent. In parti cular, a rapid formation of cubic phases at pH 5.0 is observed in the presence of this fusion peptide. The ability of the fusion peptide to promote cubic phases exhibits the same dependence on the pH as does th e fusogenicity of the intact virus. It is proposed that the peptide pr omotes cubic phases at pH 5.0 by changing the kinetics of the lamellar to inverted phase transitions.