PEPTIDE BINDING DOMAINS DETERMINED THROUGH CHEMICAL MODIFICATION OF THE SIDE-CHAIN FUNCTIONAL-GROUPS

A clear understanding of the specific secondary structure and binding domain resulting from the interactions of proteins and peptides with l ipid surfaces will provide insight into the specific functions of biol ogically active molecules. We have shown in earlier studies that the s tationary phases used in reverse-phase high-performance liquid chromat ography represent a model artificial lipid surface for the study of in duced conformational states of peptides on lipid interaction. We have now used reverse-phase high-performance liquid chromatography to deter mine the binding domains of peptides and, by extension, of proteins to a lipid surface. This approach consists of performing chemical modifi cations of specific amino acid side-chain functionalities after the in teraction of the peptides with the reverse-phase high-performance liqu id chromatography C-18 groups. The susceptibility to oxidation was als o studied after binding of the same peptides to liposomes. Oxidation o f a single methionine residue ''walked'' through an amphipathic alpha- helical 18-mer peptide was selected to illustrate this approach. The e xtent of oxidation was found to be clearly dictated by the accessibili ty of the methionine residue to the aqueous mobile phase. The binding domain found for the peptide in its lipid-induced conformational state was unequivocally the entire hydrophobic face of the amphipathic alph a-helix.