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类，特别是它们的甘油-1-磷酸(G-1-P)主干。G-1-P脱氢酶是类脂G-1-P骨架形成的关键酶，广泛存在于产甲烷菌、嗜热菌、嗜热菌和极端嗜盐菌等多种古生菌中。编码该酶的基因(EGSA)在所有已公布基因组序列的古生菌中也被检测到。DHAP与两个香叶基香叶基发生醚化反应生成的古碳酸又被CTP活化。产品为CDP-考古醇。本研究建立了CDP-考古醇合酶和始动基丝氨酸合酶的底物专一性。CDP-考古酚合成酶是以香叶基香叶基为碳链的底物专一性的酶。它不识别甘油磷酸主链或醚键的立体结构。因为合成酶不区分具有不饱和和饱和烃、醚键和酯键的底物，也不区分甘油磷酸主链的立体结构。除了最适温度外，古生菌作为合成酶的酶学性质与芽孢杆菌磷脂酰丝氨酸合成酶非常相似，氨基酸序列也有很大的相似性。这些结果表明，古生菌的合成酶和细菌的磷脂酰丝氨酸合成酶有共同的祖先。

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.