Secondary structures of proteins and peptides in amphiphilic environments. (A review)

Many peptides and proteins that act at lipid--water interfaces assume a unique amphiphilic secondary structure which is induced by the anisotropy of the interface. By using synthetic peptides in which these inducible amphiphilic structures have been optimized, one can show that the amphiphilic alpha helix is a functional determinant of representative apolipoproteins, peptide toxins, and peptide hormones. By increasing the amphiphilicity of the structurally important regions of the molecule, one can enhance the biological activity of the peptide even beyond that of the naturally occurring polypeptide. It is proposed that rigid amphiphilic secondary structures such as alpha helix, beta sheet, or pi helix will be found in most medium-sized peptides acting at membranes and lipid--water interfaces.