Acquisition of Fyn-selective SH3 domain ligands via a combinatorial library strategy.

A stepwise library-based strategy has been employed to acquire a potent ligand for the SH3 domain of Fyn, a Src kinase family member that plays a key role in T cell activation. The easily automated methodology is designed to identify potential interaction sites that circumscribe the protein/peptide binding region on the SH3 domain. The library protocol creates peptide/nonpeptide chimeras that are able to bind to these interaction sites that are otherwise inaccessible to natural amino acid residues. The peptide-derived lead and the Fyn-SH3 domain form a complex that exhibits a K(D) of 25 +/- 5 nM, approximately 1000-fold more potent than that displayed by the corresponding conventional peptide ligand. Furthermore, the lead ligand exhibits selectivity against SH3 domains derived from other Src kinases, in spite of a sequence identity of approximately 80%.