THE PTB DOMAIN - A NEW-PROTEIN MODULE IMPLICATED IN SIGNAL-TRANSDUCTION

Src homology 2 (SH2) domains have been identified in a large number of proteins involved in signal transduction downstream of receptor tyrosine kinases. They allow cytoplasmic signalling proteins to bind specifically to other polypeptides that are phosphorylated on tyrosine in response to growth factor stimulation. A novel phosphotyrosine-binding (PTB) domain has been identified recently in the amino terminus of Shc, an adaptor molecule that appears to be involved in Ras activation. PTB domains are longer than SH2 domains, and recognize phosphotyrosine in the context of aminoterminal residues, in contrast to SH2 domains, which recognize them in the context of carboxy-terminal residues.