Tight‐binding inhibitory sequences against pp60c−src identified using a random 15‐amino‐acid peptide library

A bacteriophage peptide library containing a random 15-amino-acid insert was screened for identification of peptide sequence(s) that bind pp60(c-src). Sequencing the random insert from more than 100 virions indicated that more than 60% of the phage virions that bound to this enzyme contained a GXXG sequence motif in which X was frequently a hydrophobic residue. The GXXG sequence was often repeated as GXXGXXG. Two nonameric peptides were synthesized to determine whether or not the peptide inhibits pp60(c-src) tyrosine kinase activity and the importance of the glycine residues within this sequence. The peptide containing glycine had a Ki of 24 microM, whereas replacing the glycines with proline increased the Ki value to 3.1 mM.