Description
Zap-70, a Syk-family protein tyrosine kinase, plays a critical role in mediating T cell signal transduction in response to T cell receptor (TCR) activation (1). TCR-mediated activation of the Src-family kinases, Lck and Fyn, results in tyrosine phosphorylation of the TCR zeta and CD3 chains. These domains serve as targets for binding of ZAP-70 via its tandem SH2 domains. This binding correlates with activation of ZAP-70, a critical event in T cell activation (2). Following TCR engagement, ZAP-70 is phosphorylated on several tyrosine residues, presumably by two mechanisms: an autophosphorylation and a trans-phosphorylation by the Src-family tyrosine kinase, Lck. Phosphorylation of Tyr319 is required for full activation and increased positive downstream regulation by ZAP-70 (3). |