Phosphatidic acid (PA), the central intermediate in membrane phospholipid synthesis, is generated by two acyltransferases in a pathway conserved in all life forms. The second step in this pathway is catalyzed by 1-acyl-sn-glycerol-3-phosphate acyltransferase, called PlsC in bacteria. Here we present the crystal structure of PlsC from Thermotoga maritima, revealing an unusual hydrophobic/aromatic N-terminal two-helix motif linked to an acyltransferase αβ-domain that contains the catalytic HX₄D motif. PlsC dictates the acyl chain composition of the 2-position of phospholipids, and the acyl chain selectivity 'ruler' is an appropriately placed and closed hydrophobic tunnel. We confirmed this by site-directed mutagenesis and membrane composition analysis of Escherichia coli cells that expressed mutant PlsC. Molecular dynamics (MD) simulations showed that the two-helix motif represents a novel substructure that firmly anchors the protein to one leaflet of the membrane. This binding mode allows the PlsC active site to acylate lysophospholipids within the membrane bilayer by using soluble acyl donors.

中文翻译：

---

两个螺旋基序将溶血磷脂酸酰基转移酶活性位点定位在膜双层内进行催化

磷脂酸（PA）是膜磷脂合成的主要中间产物，它是由两种酰基转移酶以所有生命形式均保守的途径生成的。该途径的第二步被1-酰基-sn-甘油-3-磷酸酰基转移酶催化，在细菌中称为PlsC。这里，我们提出从PLSC的晶体结构海栖热袍，露出一个不寻常的疏水/芳族的N-末端的两个螺旋连接至酰基转移酶基序α β结构域包含催化HX ₄D主题。PlsC指示磷脂的2-位的酰基链组成，并且酰基链选择性“规则”是适当放置和闭合的疏水通道。我们通过定点诱变和表达突变PlsC的大肠杆菌细胞膜组成分析证实了这一点。分子动力学（MD）模拟表明，两个螺旋基序代表了一种新的子结构，该结构将蛋白质牢固地锚定在膜的一个小叶上。该结合模式允许PlsC活性位点通过使用可溶性酰基供体在膜双层内酰化溶血磷脂。