Catalytic domain of Class II Phosphoinositide 3-kinase beta
PI3Ks catalyze the transfer of the gamma-phosphoryl group from ATP to the 3-hydroxyl of the inositol ring of D-myo-phosphatidylinositol (PtdIns) or its derivatives. The class II beta isoform, PI3K-C2beta, contributes to the migration and survival of cancer cells. It regulates Rac activity and impacts membrane ruffling, cell motility, and cadherin-mediated cell-cell adhesion. PI3Ks play an important role in a variety of fundamental cellular processes, including cell motility, the Ras pathway, vesicle trafficking and secretion, immune cell activation and apoptosis. They can be divided into three main classes (I, II, and III), defined by their substrate specificity, regulation, and domain structure. Class II PI3Ks preferentially use PtdIns as a substrate to produce PtdIns(3)P, but can also phosphorylate PtdIns(4)P. They function as monomers and do not associate with any regulatory subunits. Class II enzymes contain an N-terminal Ras binding domain, a lipid binding C2 domain, a PI3K homology domain of unknown function, an ATP-binding cataytic domain, a Phox homology (PX) domain, and a second C2 domain at the C-terminus. The PI3K catalytic domain family is part of a larger superfamily that includes the catalytic domains of other kinases such as the typical serine/threonine/tyrosine protein kinases (PKs), aminoglycoside phosphotransferase, choline kinase, and RIO kinases.