MEMBRANE INTERACTION OF SMALL N-MYRISTOYLATED PEPTIDES - IMPLICATIONSFOR MEMBRANE ANCHORING AND PROTEIN-PROTEIN ASSOCIATION

The effect of the covalent attachment of a myristoyl moiety to the N-t erminal glycine residue in proteins, N-myristoylation, on lipid-protei n interactions was investigated in a model system using magnetic reson ance spectroscopic methods. Two peptides with sequences conserved amon g known N-myristoylated proteins were chosen for this study. Using two -dimensional nuclear magnetic resonance techniques, it was shown that N-myristoylation results in an aggregation of both peptides in solutio n, although they lack well defined folded conformations in solution ei ther when chemically N-myristoylated or when nonacylated. The interact ion of the acylated peptides with lipid bilayers was investigated usin g spin label electron spin resonance and H-2 NMR techniques. The resul ts show that when bound to membranes, the covalently linked myristoyl chain of one of the peptides is directly inserted into or anchored to the lipid bilayer. The binding of the other peptide with membranes is effected by interactions between amino acid residues and the phospholi pid headgroups. In this case, the covalently linked myristoyl moiety i s most likely not in direct contact with the acyl chains of the host l ipid bilayer. Rather, the N-myristoyl chains stabilize the peptide agg regate by forming a hydrophobic core. Measurements of peptide binding to membranes showed that N-myristoylation affects both the lipid:pepti de stoichiometry at saturation and the equilibrium binding constant, i n a manner that is consistent with the structural information obtained by magnetic resonance methods.