Department of Structural Biology, Max Planck Institute of Biophysics, Max von Laue Strasse 3, 60438, Frankfurt am Main, Germany.
Nat Commun. 2021 Nov 30;12(1):6982. doi: 10.1038/s41467-021-27281-w.
Phospholipids are the major components of the membrane in all type of cells and organelles. They also are critical for cell metabolism, signal transduction, the immune system and other critical cell functions. The biosynthesis of phospholipids is a complex multi-step process with high-energy intermediates. Several enzymes in different metabolic pathways are involved in the initial phospholipid synthesis and its subsequent conversion. While the "Kennedy pathway" is the main pathway in mammalian cells, in bacteria and lower eukaryotes the precursor CDP-DAG is used in the de novo pathway by CDP-DAG alcohol O-phosphatidyl transferases to synthetize the basic lipids. Here we present the high-resolution structures of phosphatidyl serine synthase from Methanocaldococcus jannaschii crystallized in four different states. Detailed structural and functional analysis of the different structures allowed us to identify the substrate binding site and show how CDP-DAG, serine and two essential metal ions are bound and oriented relative to each other. In close proximity to the substrate binding site, two anions were identified that appear to be highly important for the reaction. The structural findings were confirmed by functional activity assays and suggest a model for the catalytic mechanism of CDP-DAG alcohol O-phosphatidyl transferases, which synthetize the phospholipids essential for the cells.
磷脂是所有类型的细胞和细胞器膜的主要成分。它们对于细胞代谢、信号转导、免疫系统和其他关键细胞功能也至关重要。磷脂的生物合成是一个复杂的多步骤过程，涉及高能中间体。不同代谢途径中的几种酶参与初始磷脂合成及其后续转化。虽然“肯尼迪途径”是哺乳动物细胞的主要途径，但在细菌和低等真核生物中，CDP-DAG 前体被 CDP-DAG 醇 O-磷酸转移酶用于从头途径，以合成基本脂质。在这里，我们展示了 Methanocaldococcus jannaschii 中磷脂丝氨酸合酶的高分辨率结构，该结构在四种不同状态下结晶。对不同结构的详细结构和功能分析使我们能够确定底物结合位点，并展示 CDP-DAG、丝氨酸和两个必需金属离子如何相互结合和定向。在靠近底物结合位点的地方，鉴定出了两个阴离子，它们似乎对反应非常重要。结构发现通过功能活性测定得到了证实，并提出了用于合成细胞必需磷脂的 CDP-DAG 醇 O-磷酸转移酶的催化机制模型。
