Viral fusion peptides: A tool set to disrupt and connect biological membranes

The structure and function of viral fusion peptides are reviewed. The fusio n peptides of influenza virus hemagglutinin and human immunodeficiency viru s are used as paradigms. Fusion peptides associated with lipid bilayers are conformationally polymorphic. Current evidence suggests that the fusion-pr omoting state is the obliquely inserted alpha -helix. Fusion peptides also have a tendency to self-associate into beta -sheets at membrane surfaces. A lthough the conformational conversion between alpha- and beta -states is re versible under controlled conditions, its physiological relevance is not ye t known. The energetics of peptide insertion and self-association could be measured recently using more soluble "second generation" fusion peptides. F usion peptides have been reported to change membrane curvature and the stat e of hydration of membrane surfaces. The combined results are built into a model for the mechanism by which fusion peptides are proposed to assist in biological membrane fusion.