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 Å and 3.8 Å, 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.

磷脂酰胆碱（PC）和磷脂酰乙醇胺（PE）是真核细胞膜的两种主要成分，在维持膜完整性、脂滴生物发生、自噬体形成以及脂蛋白形成和分泌中发挥重要作用。胆碱/乙醇胺磷酸转移酶 1 (CEPT1) 通过将取代的磷酸基团从 CDP-胆碱/乙醇胺转移到二酰基甘油来催化肯尼迪途径中 PC 和 PE 生物合成的最后一步。在这里，我们展示了人类 CEPT1 及其与 CDP-胆碱复合物的冷冻电镜结构，分辨率分别为 3.7 Å 和 3.8 Å。CEPT1 是一个二聚体，每个原聚体有 10 个跨膜片段 (TM)。TM 1-6 构成一个保守的催化结构域，其内部疏水室可容纳类似 PC 的密度。结构观察和生化表征表明疏水室在催化过程中协调酰基尾部。与 CDP-胆碱形成的复合物结构中类似 PC 的密度消失，表明潜在的底物触发产物释放机制。