Development of a selective pseudosubstrate-based peptide inhibitor of pp60^c-scr protein tyrosine kinase

Using a combinatorial peptide library method, we identified YIYGSFK as an efficient and specific peptide substrate for pp60^c-scr protein tyrosine kinase (PTK) [Lam et al., Int. J. Pept. Protein Res., 45 (1995) 587]. Employing YIYGSFK as a template, we synthesized and evaluated a series of pseudosubstrate-based inhibitors for pp60^c-scr. We found that the efficiency of a given inhibitor was highly dependent on the specific tyrosine analog used at the phosphorylation site of the substrate. One of these pseudosubstrate inhibitors, YI(2′-Nal)GSFK, selectively inhibited the kinase activity of pp60^c-scr, with a K_i of 24 μM. This peptide inhibitor exhibited selectivity for pp60^c-scr as compared to other PTKs tested, such as c-Abl and Bcr-Abl. Our results suggest that selective inhibitors for a specific PTK can be developed when the structure of a specific and efficient small peptide substrate for this PTK can be used as a template for structure modification.