A peptide library approach identifies a specific inhibitor for the ZAP-70 protein tyrosine kinase

We utilized a novel peptide library approach to identify specific inhibitor s of ZAP-70, a protein Tyr kinase involved in T cell activation. By screeni ng more than 6 billion peptides oriented by a common Tyr residue for their ability to bind to ZAP-70, we determined a consensus optimal peptide. A Phe -for-Tyr substituted version of the peptide inhibited ZAP-70 protein Tyr ki nase activity by competing with protein substrates (K-I of 2 muM). The rela ted protein Tyr kinases, Lck and Syk, were not significantly inhibited by t he peptide. When introduced into intact T cells, the peptide blocked signal ing downstream of ZAP-70, including ZAP-70-dependent gene induction, withou t affecting upstream Tyr phosphorylation. Thus, screening Tyr-oriented pept ide libraries can identify selective peptide inhibitors of protein Tyr kina ses.