Tandem SH2 domains of ZAP-70 bind to T cell antigen receptor ζ and CD3∈ from activated Jurkat T cells

A proximal and critical biochemical event upon T cell antigen receptor (TCR) stimulation is the activation of a protein tyrosine kinase (PTK) pathway. ZAP-70, a PTK of the p72^syk family, associates with phosphorylated TCR subunits upon TCR stimulation. Here we report that the tandem SH2 domains of ZAP-70, expressed as a fusion protein, bind to tyrosine-phosphorylated CDS3∈ and TCRζ from activated Jurkat T cell lysates. The single N-and C-terminal SH2 domains Of ZAP-70, expressed separately, do not bind these TCR subunits. In comparison to fusion proteins containing SH2 domains from other proteins, the tandem SH2 domains of ZAP-70 demonstrate a remarkably restricted repertoire of protein binding, binding only TCRζ and CD3∈. ZAP-70 is also recovered in the binding assay, but this is likely to be a consequence of its interaction with multiple SH2 binding sites on the ζ-ζ and CD3∈-containing dimers.