BINDING AFFINITIES OF THE SH2 DOMAINS OF ZAP-70, P(56)LCK AND SHC TO THE ZETA-CHAIN ITAMS OF THE T-CELL RECEPTOR DETERMINED BY SURFACE-PLASMON RESONANCE

The zeta chains of the T cell receptor complex play a critical role in the initiation of proximal signaling events upon T cell activation, T hree pairs of potential tyrosine phosphorylation sites are located wit hin the cytoplasmic domains of the zeta chains, Subsequent to engageme nt of the T cell receptor, one or more of these tyrosine residues is p hosphorylated, Tbe phosphotyrosine residues, along with flanking amino acids, form an activation motif (and are shared by signaling subunits in the TCR, B cell receptor, and Fc gamma RI) termed tyrosine-based a ctivation motifs (ITAMs). ITAMs serve as binding sites for SH2 domain- containing proteins, Recent evidence suggests that the zeta chains pro vide docking space for several key signal transduction molecules such as ZAP-70, p(56)lck, and Shc. To determine if ZAP-70, p(56)lck, and Sh e bind to particular zeta chain ITAM sequences, quantitative free-solu tion measurements of binding affinities (K-d) were obtained by use of surface plasmon resonance technology, The results indicate that bindin g affinities of distinct SH2 domains to individual and paired phosphor ylation sites greatly differ, and may dictate the sequence of signal t ransduction events.