KINETICS OF P56(LCK) AND P60(SRC) SRC HOMOLOGY-2 DOMAIN BINDING TO TYROSINE-PHOSPHORYLATED PEPTIDES DETERMINED BY A COMPETITION ASSAY OR SURFACE-PLASMON RESONANCE

Src homology 2 (SH2) domains are phosphotyrosine-binding modules found within various signal-transducing proteins. We have determined hy I-125 competition assay and surface plasmon resonance that the SH2 domains of Src and Lck bind to a variety of phosphopeptides with similar affinity and specificity. Both bound with highest affinity [K(d(app)) almost-equal-to 3.7 nM; k(a) = 2.4 x 10(5) M-1.s-1; k(d) = 1.2 x 10(-3) s-1] a phosphopeptide having a Tyr(P)-Glu-Glu-Ile motif found in the hamster polyomavirus middle-sized tumor antigen. Intermediate affinity (5- to 40-fold lower) was observed with phosphopeptides corresponding to the regulatory domains of Src and Lck, containing Tyr527 and Tyr505, respectively. Lowest affinity (80- to 300-fold lower) was observed with phosphopeptides corresponding to phosphorylated tyrosines of GTPase-activating protein, insulin receptor substrate 1, and SH2 domain-containing protein-tyrosine-phosphatase 1.