Abstract
Cas-family proteins serve as docking proteins in integrin-mediated signal transduction. The founding member of this family, p130Cas, becomes tyrosine-phosphorylated in response to extracellular stimuli such as integrin-mediated cell adhesion and ligand engagement of receptor tyrosine kinases. Cas proteins are large multidomain molecules that transmit signals as intermediaries through interactions with signaling molecules such as FAK and other tyrosine kinases, as well as tyrosine phosphatases. After Cas is tyrosine-phosphorylated, it acts as a docking protein for binding SH2 domains of Src-family kinases. In order to examine the structural basis for a key step in propagation of signals by Cas, one of the major SH2-binding sites of Cas has been crystallized in complex with the SH3-SH2 regulatory domains of the Src-family kinase Lck. Crystallization conditions were identified by high-throughput screening and optimized with multiple rounds of seeding. The crystals formed at 295 K in space group P2(1)2(1)2(1), with unit-cell parameters a = 77.4, b = 107.3, c = 166.4 A, and diffract to 2.7 A resolution.