Lipid Biosynthesis in archaea-Exploring its uniqueness and evolutionary position

古细菌膜脂的核心结构具有一些独特的性质，使古细菌区别于其他生物，即细菌和真核生物。(S)-2,3-二- o -香叶基香叶基磷酸甘油酯合成酶催化香叶基基从二磷酸香叶基转化为(S)-3- o -香叶基甘油酯磷酸，参与古细菌膜脂的生物合成。已知UbiA戊烯基转移酶家族的酶在呼吸醌、血红素、叶绿素、维生素E和紫草素的生物合成中催化戊烯基转移到具有疏水环结构的各种受体。发现嗜热酸性古菌S.solfataricus在其基因组中编码3个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、纯化并鉴定。放射分析和质谱分析数据表明，该酶特异性催化(S)-2,3-二- o -香叶酰甘油酯磷酸的生物合成。该酶的同源物几乎在所有古细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。利用UbiA戊烯基转移酶家族的一些典型成员及其来自s.s solfataricus的同源物的氨基酸序列构建的系统发育树表明，除了(S)-2,3-二- o -香叶酰香叶酰甘油磷酸合成酶外，另外两个s.s solfataricus同源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细菌戊烯基转移酶可能是该蛋白家族的原型，古细菌可能在戊烯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.