Phosphorylated T Cell Receptor ζ-Chain and ZAP70 Tandem SH2 Domains Form a 1:3 Complex In Vitro

Abstract

The ζ polypeptide is part of the T cell antigen receptor (TCR). The ζ-chain contributes to efficient cell-surface expression of the TCR and accounts for part of its signal transduction capability. TCR recognition triggers a complex set of events that result in cellular activation. The protein tyrosine kinase (PTK) Lck phosphorylates the ζ-chain, which in turn associates with another PTK, ZAP70, and stimulates its phosphorylation activity. Here we report the expression of the intracellular part of the ζ-chain and its biochemical characterization. The recombinant protein does not dimerize by itself in solution. Circular-dichroic analysis reveals a random coil conformation. ζ, phosphorylated using recombinant Lck, associates with recombinant ZAP70 tandem-SH2 domains. All three T cell activation motifs in ζ bind ZAP70 tandem-SH2 domains <i>in vitro</i>, forming a 1:3 complex. This result extends the picture, derived from earlier studies, of a mechanism for signal amplification.