 The proline-rich region of paxillin specifically binds to the second SH3 domain of ponsin, which occurs after the onset of the myogenic differentiation and with expression restricted to costameres.We also know that the binding of paxillin to focal adhesion kinase (FAK) is critical for directing paxillin function.The phosphorylation of FAK at serine-910 regulates the interaction of FAK with paxillin, and controls the stability of paxillin at costameres in cardiomyocytes, with phosphorylation reducing the half-life of paxillin.