In vitro biosynthesis of enantiomeric ether polar lipids in Archaea

最基本的特征。古菌与细菌/真核菌的区别在于膜醚型极性脂质，特别是它们的sn-甘油-1-磷酸（G-1-P）骨架。G-1-P脱氢酶是形成脂质G-1-P骨架的关键酶，在几种古菌中普遍存在，包括产甲烷菌、超嗜热菌、嗜酸菌和极端嗜盐菌。编码该酶的基因（egsA）也在所有已发表的古菌基因组序列中进行了同源性搜索。由dhp与两个香叶基醚化形成的古绿酸，又被CTP激活。产物为CDP-archaeol。本研究建立了cdp -古酚合成酶-和古酰丝氨酸合成酶的底物特异性。cdp -古酚合成酶对以香叶基为烃链的底物具有特异性。它不能识别甘油磷酸主链或醚键的立体结构。AS合酶不能区分底物中不饱和和不饱和碳氢化合物，醚键和酯键，或甘油磷酸酯骨架的立体结构。古细菌AS合成酶的酶学性质与芽孢杆菌磷脂酰丝氨酸合成酶除最适温度外基本相似，氨基酸序列也具有显著的相似性。这些结果表明，古细菌AS合成酶与细菌磷脂酰丝氨酸合成酶具有共同的祖先。

The most fundamental characteristics. that distinguishes Archaea from Bacteria/Eucarya is membrane ether-type polar lipids, especially their sn-glycerol-1-phosphate (G-1-P) backbone. G-1-P dehydrogenase, which is the key enzyme for the formation of lipid G-1-P backbone, was found ubiquitously in several species of Archaea including methanogens, hyperthermophiles, an acidothermophile, and an extreme halophile as far as analysed. The gene (egsA) encoding the enzyme was also detected by homology search in all the Archaea whose genome sequences have been published. Archaeitidic acid, which is formed from DHAP by etherification with two geranylgeranyl groups, was in turn activated by CTP. The product is CDP-archaeol. The substrate specificities of CDP-archaeol synthase- and archetidylserine synthase were established in this study. CDP-archaeol synthase was specific to the substrate with geranylgeranyl groups as hydrocarbon chains. It did not recognized stereostructure of glycerophosphate backbone or ether bonds. AS synthase did not discriminate substrates with unsaturated and saturated hydrocarbons, ether bonds and ester bonds, or stereostructures of glycerophosphate backbone. The enzymatic properties of archaeal AS synthase were quite similar to Bacillus phosphatidylserine synthase except for the optimal temperature, and the amino acid sequences showed significant similarity. These results suggested archaeal AS synthase and bacterial phosphatidylserine synthase share their ancestor.