This group is composed of eukaryotic choline kinase, ethanolamine kinase, and similar proteins. ChoK catalyzes the transfer of the gamma-phosphoryl group from ATP (or CTP) to its substrate, choline, producing phosphorylcholine (PCho), a precursor to the biosynthesis of two major membrane phospholipids, phosphatidylcholine (PC), and sphingomyelin (SM). Although choline is the preferred substrate, ChoK also shows substantial activity towards ethanolamine and its N-methylated derivatives. ETNK catalyzes the transfer of the gamma-phosphoryl group from CTP to ethanolamine (Etn), the first step in the CDP-Etn pathway for the formation of the major phospholipid, phosphatidylethanolamine (PtdEtn). Unlike ChoK, ETNK shows specific activity for its substrate and displays negligible activity towards N-methylated derivatives of Etn. ChoK plays an important role in cell signaling pathways and the regulation of cell growth. The ChoK subfamily is part of a larger superfamily that includes the catalytic domains of other kinases, such as the typical serine/threonine/tyrosine protein kinases (PKs), RIO kinases, actin-fragmin kinase (AFK), and phosphoinositide 3-kinase (PI3K).
Jiyao W et al.(2023). "The conserved domain database in 2023.",