Lee Eunju, Cho Gyuhyeok, Kim Jungwook
Department of Chemistry, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea.
Sci Adv. 2024 Dec 20;10(51):eadq4624. doi: 10.1126/sciadv.adq4624. Epub 2024 Dec 18.
Phosphatidylserine synthase (PssA) is essential in the biosynthesis of phosphatidylethanolamine, a major phospholipid of bacterial membranes. A peripheral membrane protein PssA can associate with the cellular membrane in its active state or exist in the cytosol in an inactive form. The membrane-bound enzyme acts on cytidine diphosphate diacylglycerol (CDP-DG) to form cytidine monophosphate and a covalent intermediate, which is subsequently targeted by serine to produce phosphatidylserine. Here, we present two crystal structures of PssA, one complexed with CDP-DG and the other without. The lipid-bound structure mimics the Michaelis complex before the formation of a covalent intermediate, revealing key determinants for substrate recognition and catalysis. Notably, membrane-free PssA is in a monomer-dimer equilibrium, with only the monomer capable of associating with the membrane, suggesting a regulatory mechanism for phospholipid biosynthesis dependent on the oligomerization state of the enzyme.
磷脂酰丝氨酸合酶（PssA）在磷脂酰乙醇胺的生物合成中至关重要，磷脂酰乙醇胺是细菌细胞膜的主要磷脂。外周膜蛋白PssA在其活性状态下可与细胞膜结合，或以无活性形式存在于细胞质中。膜结合酶作用于胞苷二磷酸二酰甘油（CDP-DG）形成胞苷一磷酸和共价中间体，随后丝氨酸作用于该中间体生成磷脂酰丝氨酸。在此，我们展示了PssA的两种晶体结构，一种与CDP-DG复合，另一种未复合。脂质结合结构模拟了共价中间体形成前的米氏复合物，揭示了底物识别和催化的关键决定因素。值得注意的是，无膜PssA处于单体-二聚体平衡状态，只有单体能够与膜结合，这表明磷脂生物合成的调节机制取决于酶的寡聚化状态。
