THE ROLE OF AMPHIPATHICITY IN THE FOLDING, SELF-ASSOCIATION AND BIOLOGICAL-ACTIVITY OF MULTIPLE SUBUNIT SMALL PROTEINS

The effect that altering amphipathicity has on the folding process and self association of melittin, a small model protein, has been investi gated using single amino acid substitutions of lysine 7, a residue dis tant from the contact residues involved in the hydrophobic core of tet rameric melittin. While substitutions of such a residue were not expec ted to interfere with the packing process, the largest alterations in the potential overall amphipathicity of melittin were found to prevent the folding into an alpha-helical conformation to occur and, in turn, to prevent the self association. Amphiphathic alpha-helices were foun d to be a key determining feature in the early folding process of the self association of peptides and protein segments. Those substitutions , which prevented the inducible amphipathic folding ability, were also found to result in a loss in hemolytic and antimicrobial activity. Th ese results, combined with studies of the binding to artificial liposo mes and to polysialic acids, indicate that the losses in activity were due to an initial inability to be induced into an amphipathic alpha-h elix and to self associate. Ultimately, melittins's self association i s proposed to be required to penetrate the carbohydrate barrier in bio logical membranes.