SH2-MEDIATED AND SH3-MEDIATED INTERACTIONS BETWEEN FOCAL ADHESION KINASE AND SRC

Intramolecular SH2 and SH3 interactions mediate enzymatic repression o f the Src kinases. One mechanism of activation is disruption of these interactions by the formation of higher affinity SH2 and SH3 interacti ons with specific Ligands. We show that a consensus Src SH3-binding si te residing upstream of the Src SH2-binding site in FAK can function a s a ligand for the Src SH3 domain. Surface plasmon resonance experimen ts indicate that a FAK: peptide containing both the Src SH2 and SH3-bi nding sites exhibits increased affinity for Src, Furthermore, the pres ence of both sites in vitro more potently activates c-Src. A FAK mutan t (FAK(Pro-2)) with substitutions destroying the SH3-binding site show s reduced binding to Src in vivo, This mutation also reduces Src-depen dent tyrosine phosphorylation on the mutant itself and downstream subs trates, such as paxillin, These observations suggest that an SH3-media ted interaction between Src-like kinases and FAK may be important for complex formation and downstream signaling in vivo.