TANDEM SH2 DOMAINS CONFER HIGH SPECIFICITY IN TYROSINE KINASE SIGNALING

SH2 domain proteins transmit intracellular signals initiated by activa ted tyrosine kinase-linked receptors. Recent three-dimensional structu res suggest mechanisms by which tandem SH2 domains might confer higher specificity than individual SH2 domains, To test this, binding studie s were conducted with tandem domains from the five signaling enzymes: phosphatidylinositol 3-kinase p85, ZAP-70, Syk, SHP-2, and phospho; li pase C-gamma 1. Bisphosphorylated TAMs (tyrosine-based activation moti fs) were derived from biologically relevant sites in platelet-derived growth factor, T cell, B cell, and high affinity IgE receptors and the receptor substrates IRS-1 (insulin receptor substrate-1) and SHPS-1/S IRP. Each tandem SH2 domain binds a distinct TAM corresponding to its appropriate biological partner with highest affinity (0.5-3.0 nM). Alt ernative TAMs bind the tandem SH2 domains with 1,000- to >10,000- fold lower affinity than biologically relevant TAMs. This level of specifi city is significantly greater than the similar to 20-50-fold typically seen for individual SH2 domains, We conclude that high biological spe cificity is conferred by the simultaneous interaction of two SH2 domai ns in a signaling enzyme with bisphosphorylated TAMs in activated rece ptors and substrates.