Identification of FAK substrate peptides via colorimetric screening of a one-bead one-peptide combinatorial library

Abstract

Focal adhesion kinase (FAK) is a protein tyrosine kinase that is associated with regulating cellular functions such as cell adhesion and migration and has emerged as an important target for cancer research. Short peptide substrates that are selectively and efficiently phosphorylated by FAK have not been previously identified and tested. Here we report the synthesis and screening of a one-bead one-peptide combinatorial library to identify novel substrates for FAK. Using a solid-phase colorimetric antibody tagging detection platform, the peptide beads phosphorylated by FAK were sequenced via Edman degradation and then validated through radioisotope kinetic studies with [γ-(32)P] ATP to derive Michaelis-Menton constants. The combination of results gathered from both colorimetric and radioisotope kinase assays led to the rational design of a second generation of FAK peptide substrates. Out of all the potential peptide substrates evaluated, the most active was GDYVEFKKK with a K(M) = 92 μM and a Vmax = 1920 nmol/min/mg. Peptide substrates discovered within this study may be useful diagnostic tools for future kinase investigations and may lead to novel therapeutic agents.

Keywords: FAK; colorimetric; combinatorial peptide library; substrate specificity; tyrosine kinase.