In vitro biosynthesis of enantiomeric ether polar lipids in Archaea

最基本的特征。区别于细菌/真核生物的是膜醚型极性脂质，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，据分析，它普遍存在于几种微生物中，包括产甲烷菌、超嗜热菌、嗜酸热菌和极端嗜盐菌。通过同源性搜索，在所有已发表基因组序列的大肠杆菌中也检测到编码该酶的基因（egsA）。由DHAP通过与两个香叶基香叶基的醚化形成的异麦芽酚酸又被CTP活化。该产品为CDP-古菌。本研究建立了CDP-古菌醇合酶和archetidylserine合酶的底物特异性。CDP-古醇合酶对以香叶基香叶基为烃链的底物具有特异性。它不识别甘油磷酸骨架或醚键的立体结构。AS合成酶没有歧视底物与不饱和和饱和烃，醚键和酯键，或立体结构的甘油磷酸骨架。古生菌AS合成酶的酶学性质与芽孢杆菌磷脂酰丝氨酸合成酶相似，但最适温度不同，氨基酸序列也有很大的相似性。这些结果表明古细菌AS合成酶和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.