Catalytic domain of Class IB Phosphoinositide 3-kinase gamma
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. PI3Kgamma signaling controls diverse immune and vascular functions including cell recruitment, mast cell activation, platelet aggregation, and smooth muscle contractility. It associates with one of two regulatory subunits, p101 and p84, and is activated by G-protein-coupled receptors (GPCRs) by direct binding to their betagamma subunits. It contains an N-terminal Ras binding domain, a lipid binding C2 domain, a PI3K homology domain of unknown function, and a C-terminal ATP-binding cataytic domain. PI3Ks can be divided into three main classes (I, II, and III), defined by their substrate specificity, regulation, and domain structure. Class I PI3Ks are the only enzymes capable of converting PtdIns(4,5)P2 to the critical second messenger PtdIns(3,4,5)P3. Class I enzymes are heterodimers and exist in multiple isoforms consisting of one catalytic subunit (out of four isoforms) and one of several regulatory subunits. They are further classified into class IA (alpha, beta and delta) and IB (gamma). 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.
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