Lipid Biosynthesis in archaea-Exploring its uniqueness and evolutionary position

古生菌的膜脂核心结构具有一些独特的性质，使古生菌有别于细菌和真核生物。(S)-2，3-二-O-香叶基香叶基甘油基磷酸酯合成酶催化香叶基香叶基二磷酸转移到(S)-3-O-香叶基香叶基甘油基磷酸酯，参与古生物膜脂的生物合成。已知的UbiA异戊烯基转移酶家族的酶催化异戊烯基团转移到各种具有疏水环结构的受体上，在呼吸醌、血红素、叶绿素、维生素E和紫草素的生物合成中。发现嗜热嗜酸古细菌S.solfararicus在其基因组中编码三种UbiA戊烯基转移酶的同源物。其中一个由SSO0583编码的同源物在大肠杆菌中表达、纯化和鉴定。放射分析和质谱分析数据表明，该酶专一性催化(S)-2，3-二O-香叶基香叶基甘油基磷酸酯的生物合成。这种酶的同源同源物在几乎所有的古生菌基因组中都有编码，这一事实清楚地表明了它们功能的重要性。根据UbiA戊烯基转移酶家族的一些典型成员的氨基酸序列及其同系物构建的系统发育树表明，另外两个不包括(S)-2，3-二-O-香叶基香叶基甘油基磷酸合成酶的同系物分别参与呼吸醌和血红素的产生。我们认为，参与膜脂生物合成的古生菌前烯基基转移酶可能是蛋白质家族的原型，古生菌可能在前烯基基转移酶的分子进化中发挥了重要作用。

The core structure of membrane lipids of archaea have some unique properties that permit archaea to be distinguished from the others, i.e., bacteria and eukaryotes. (S)-2,3-Di-O-geranylgeranylglyceryl phosphate synthase, which catalyzes the transfer of a geranylgeranyl group from geranylgeranyl diphosphate to (S)-3-O-geranylgeranylglyceryl phosphate, is involved in the biosynthesis of archaeal membrane lipids. Enzymes of the UbiA prenyltransferase family are known to catalyze the transfer of a prenyl group to various acceptors with hydrophobic ring structures in the biosynthesis of respiratory quinones, hemes, chlorophylls, vitamin E, and shikonin. The thermoacidophilic archaeon S.solfataricus was found to encode three homologues of UbiA prenyltransferase in its genome. One of the homologues encoded by SSO0583 was expressed in Escherichia coli, purified, and characterized. Radioassay and mass spectrometry analysis data indicated that the enzyme specifically catalyzes the biosynthesis of (S)-2,3-di-O-geranylgeranylglyceryl phosphate. The fact that the orthologues of the enzyme are encoded in almost all archaeal genomes clearly indicates the importance of their functions. A phylogenetic tree constructed using the amino acid sequences of some typical members of the UbiA prenyltransferase family and their homologues from S.solfataricus suggests that the two other S.solfataricus homologues, excluding the (S)-2,3-di-O-geranylgeranylglyceryl phosphate synthase, are involved in the production of respiratory quinone and heme, respectively. We propose here that archaeal prenyltransferases involved in membrane lipid biosynthesis might be prototypes of the protein family and that archaea might have played an important role in the molecular evolution of prenyltransferases.