Cortactin is an 80/85 kDa cytoskeleton protein that facilitates assembly of cortical actin. Cortactin is widely expressed in most adherent cells and is a prominent substrate of protein tyrosine kinase Src in vivo and in vitro. The protein sequence of cortactin contains multiple amino terminal tandem repeats of a unique 37 amino acid sequence, which associates with actin, and a Src homology 3 (SH3) domain at the carboxyl terminus. Between the repeat and the SH3 domain, there is an alpha helical structure followed by a proline rich region. Between the proline rich region and the SH3 domain, there are a series of Src phosphorylation sites (Tyr421, Tyr470, and Tyr486). In vitro, cortactin binds to and cross links F actin into meshworks.
