Structural basis for catalysis of human choline/ethanolamine phosphotransferase 1

Choline/ethanolamine phosphotransferase 1 (CEPT1) catalyzes the last step of the biosynthesis of PC and PE. Here, the authors present the cryo-EM structures of human CEPT1 and its complex with CDP-choline and reveal a hydrophobic chamber to accommodate the acyl tails during the catalytic process. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are two primary components of the eukaryotic membrane and play essential roles in the maintenance of membrane integrity, lipid droplet biogenesis, autophagosome formation, and lipoprotein formation and secretion. Choline/ethanolamine phosphotransferase 1 (CEPT1) catalyzes the last step of the biosynthesis of PC and PE in the Kennedy pathway by transferring the substituted phosphate group from CDP-choline/ethanolamine to diacylglycerol. Here, we present the cryo-EM structures of human CEPT1 and its complex with CDP-choline at resolutions of 3.7 & ANGS; and 3.8 & ANGS;, respectively. CEPT1 is a dimer with 10 transmembrane segments (TMs) in each protomer. TMs 1-6 constitute a conserved catalytic domain with an interior hydrophobic chamber accommodating a PC-like density. Structural observations and biochemical characterizations suggest that the hydrophobic chamber coordinates the acyl tails during the catalytic process. The PC-like density disappears in the structure of the complex with CDP-choline, suggesting a potential substrate-triggered product release mechanism.

Automated summary

This study presents the cryo-EM structures of human CEPT1 and its complex with CDP-choline, revealing a hydrophobic chamber involved in catalysis. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are vital components of eukaryotic membranes and have various important roles. The structures of CEPT1 and its complex provide insights into the catalytic mechanism and potential substrate-triggered product release.