 The N-terminal region of paxillin is rich in protein–protein interaction sites.The proteins that bind to paxillin are diverse and include protein tyrosine kinases, such as Src and focal adhesion kinase (FAK), structural proteins, such as vinculin and actopaxin, and regulators of actin organization, such as COOL/PIX and PKL/GIT.Paxillin is tyrosine-phosphorylated by FAK and Src upon integrin engagement or growth factor stimulation, creating binding sites for the adapter protein Crk.