Phosphotyrosine-containing dipeptides as high-affinity ligands for the p56(lck) SH2 domain

Src homology-2 (SH2) domains are noncatalytic motifs containing approximate ly 100 amino acid residues that are involved in intracellular signal transd uction. The phosphotyrosine-containing tetrapeptide Ac-pYEEI binds to the S H2 domain of p.56(lck) (Lck) with an affinity of 0.1 mu M. Starting from Ac -pYEEI, we have designed potent antagonists of the Lck SH2 domain which are reduced in peptidic character and in which the three carboxyl groups have been eliminated. The two C-terminal amino acids (EI) have been replaced by benzylamine derivatives and the pY + 1 glutamic acid has been substituted w ith leucine. The best C-terminal fragment identified, (S)-1-(4-isopropylphe nyl)ethylamine, binds to the Lck SH2 domain better than the C-terminal dipe ptide EI. Molecular modeling suggests that the substituents at the 4-positi on of the phenyl ring occupy the pY + 3 lipophilic pocket in the SH2 domain originally occupied by the isoleucine side chain. This new series of phosp hotyrosine-containing dipeptides binds to the Lck SH2 domain with potencies comparable to that of tetrapeptide 1.