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Catalytic domain of Class I Phosphoinositide 3-kinase 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. Class I PI3Ks are the only enzymes capable of converting PtdIns(4,5)P2 to the critical second messenger PtdIns(3,4,5)P3. In vitro, they can also phosphorylate the substrates PtdIns and PtdIns(4)P. 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). 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. 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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