cytidylyltransferase

Cytidylyltransferase refers to a family of enzymes that catalyze the transfer of a cytidylyl group from CTP to an acceptor molecule, generating a cytidylylated activated intermediate such as CDP-sugars or CDP-derivatives. Members of this family belong to the broader nucleotidyltransferase superfamily and can be soluble or membrane-associated, depending on their cellular role. They are found in bacteria, archaea, and eukaryotes, where they participate in lipid and polysaccharide biosynthesis as well as in pathways that generate activated sugar donors for glycosylation.

The general reaction catalyzed by cytidylyltransferases is: CTP + acceptor-RH → PPi + CDP-RH, where the acceptor can be a phospholipid head group, a sugar phosphate, or another organic substrate. Most enzymes in this class require divalent metal ions, commonly Mg2+ or Mn2+, to facilitate nucleotidyl transfer. The catalytic mechanism typically involves nucleophilic attack on the α-phosphate of CTP and stabilization of pyrophosphate by metal coordination.

Examples include CTP:phosphocholine cytidylyltransferase, which forms CDP-choline in the CDP-choline pathway of phosphatidylcholine biosynthesis, and CDP-diacylglycerol synthase, which generates CDP-diacylglycerol for phospholipid assembly in bacteria and eukaryotes. Other cytidylyltransferases contribute to the formation of CDP-sugars such as CDP-ethanolamine or CDP-glucose, which serve as activated donors in various glycosylation reactions and capsule biosynthesis.

Cytidylyltransferases play essential roles in membrane biogenesis and cell surface component synthesis, and their activity is often tightly regulated at the cellular level to meet metabolic demands.