MEMBRANE-BINDING OF MYRISTYLATED PEPTIDES CORRESPONDING TO THE NH2 TERMINUS OF SRC

Membrane association is required for cell transformation by pp60(v-src ) (v-Src), the product of the v-src oncogene of Rous sarcoma virus. Pr evious experiments have identified two NH2-terminal membrane-binding m otifs: a myristate (14-carbon acyl chain) attached to the NH2-terminal glycine and three basic residues at positions 5, 7, and 9 of Src. We examined the membrane binding of each motif using myristylated (myr-sr c) and nonmyristylated (nonmyr-src) peptides corresponding to the NH2 terminus of Src. All myristylated peptides partitioned equally well on to electrically neutral phosphatidylcholine vesicles (K-1 = 10(4) M(-1 )). Identical binding has been observed for simple myristylated peptid es (e.g., myr-Gly) and arises from the hydrophobic insertion of the my ristate into the bilayer. A nonmyristylated peptide corresponding to r esidues 2-16 of Src [nonmyr-src(2-16), net charge = +5] bound to vesic les containing 33% monovalent acidic phospholipids with K-1 = 10(3) M( -1), Penta(lysine) (+5 net charge) exhibits the same binding behavior, which is due to the electrostatic interaction between basic residues and acidic lipids. The corresponding myristylated peptide, myr-src(2-1 6), binds 3 orders of magnitude more strongly to vesicles containing 3 3% acidic lipids than to neutral vesicles. The resulting apparent asso ciation constant, K-1 = 10(7) M(-1), is approximately equal to the pro duct of the partition coefficients for the two individual interactions . This 10(7) M(-1) binding is sufficiently strong to anchor the Src pr otein to biological membranes. We propose a simple model that explains the observed synergism between the two peptide-membrane interactions.