Catalytic domain of the Serine/Threonine Kinase, p21-activated kinase 4
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. PAK4 regulates cell morphology and cytoskeletal organization. It is essential for embryonic viability and proper neural development. Mice lacking PAK4 die due to defects in the fetal heart. In addition, their spinal cord motor neurons showed failure to differentiate and migrate. PAK4 also plays a role in cell survival and tumorigenesis. It is overexpressed in many primary tumors including colon, esophageal, and mammary tumors. PAK4 has also been implicated in viral and bacterial infection pathways. PAK4 belongs to the group II PAKs, which contain a PBD (p21-binding domain) and a C-terminal catalytic domain, but do not harbor an AID (autoinhibitory domain) or SH3 binding sites. PAKs are Rho family GTPase-regulated kinases that serve as important mediators in the function of Cdc42 (cell division cycle 42) and Rac. The PAK subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.