Catalytic domain of Type III Phosphoinositide 4-kinase beta
PI4Ks catalyze the transfer of the gamma-phosphoryl group from ATP to the 4-hydroxyl of the inositol ring of D-myo-phosphatidylinositol (PtdIns) to generate PtdIns(4)P, the major precursor in the synthesis of other phosphoinositides including PtdIns(4,5)P2, PtdIns(3,4)P2, and PtdIns(3,4,5)P3. Two isoforms of type III PI4K, alpha and beta, exist in most eukaryotes. PI4KIIIbeta (also called Pik1p in yeast) is a 110 kDa protein that is localized to the Golgi and the nucleus. It is required for maintaining the structural integrity of the Golgi complex (GC), and is a key regulator of protein transport from the GC to the plasma membrane. PI4KIIIbeta also functions in the genesis, transport, and exocytosis of synaptic vesicles. The Drosophila PI4KIIIbeta is essential for cytokinesis during spermatogenesis. The PI4K 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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