Study on the evolution of Archaea and Bacteria from the view points of archaeal polar lipid biosynthesis

极性脂质是细胞膜不可缺少的成分。由于第一个细胞是在极性脂质发生时产生的，阐明古细菌和细菌在结构和生物合成机制上的差异，将为讨论古细菌和细菌的起源提供线索，这两种细菌在基础生物化学上存在差异。以往的研究表明，膜极性脂质中最基本的生化差异之一是甘油磷酸酯骨架的立体化学结构，并提出手性脂质的分离引发了古细菌和细菌的分化。本文对古细菌和细菌分化过程中膜极性脂类极性群的演化进行了研究。本研究表明，肌醇磷脂合成酶和甘油磷脂合成酶同属于一个酶家族，即cdp -醇磷脂酰转移酶家族，并与丝氨酸磷脂合成酶包括酯型磷脂合成酶同属一个家族。这一结论是通过对古细菌和细菌基因组的BLAST检索（以古菌丝氨酸合酶的氨基酸序列作为查询）和对甲烷古菌的古菌丝氨酸合酶的体外研究得出的。检测了单糖木酚合成酶和双糖木酚合成酶的活性，并对其进行了部分鉴定。饱和古醇和udp -葡萄糖通过两种不同的酶依次葡萄糖化。虽然古细菌中的糖脂合成酶尚未在系统发育上得到阐明，但古细菌糖脂合成的酶促反应模式与细菌相似。古细菌单葡萄糖苷醛合成酶识别脂质底物的立体结构。从以上结果可以推测，Wachtershauser提出的古细菌和细菌分化前阶段的前细胞极性脂质具有古细菌和细菌共同的和当代的极性头群。具有外消旋核心脂质和共同极性基团的极性脂质被分离为具有共同极性基团的同手性极性脂质。这是古细菌和细菌分化的原因。磷脂合成的同源酶被带入生物体的两个领域。古细菌和细菌分化后会产生立体特异性糖脂合成酶。少

Polar lipids are indispensable constituents of cellular membranes. Because the first cell came into existence at the occurrence of polar lipids, the elucidation of differences in the structure and biosynthetic mechanism between Archaea and Bacteria would give a clue to discuss the origin of Archaea and Bacteria, which show differences in the fundamental biochemistry. Previous studies revealed that one of the most fundamenntal biochemical differences was the stereochemical structure of glycerophosphate backbone of membrane polar lipids, and it was proposed that the segregation of the chiral lipids triggered off differentiation of the Archaea and Bacteria. The present study focused on the evolution of polar groups of membrane polar lipids in relation with the differentiation of Archaea and Bacteria.It was elucidated in the present study that synthases of inositol phospholipid and glycerol phospholipid belonged to the same enzyme family, CDP-alcohol phosphatidyltransferase family, along w … More ith serine phospholipid synthase including ester-type phospholipid synthases. This conclusion was drawn from BLAST search of archaeal and bacterial genomes using the amino acid sequence of archaetidylserine synthase as a query and in vitro studies of archaetidylserine synthase from a methanoarchaeon. Activities of monoglucosylarchaeol synthase and diglucosylarchaeol synthase were detected and partialy characterized. Saturated archaeol was sequentially glucosylated with UDP-glucose by two separate enzymes. Although glycolipid synthases in Archaea have not been phylogenetically elucidated, the outline of the enzymatic mode of reaction of archaeal glycolipid synthesis was the similar to bacterial counterparts. The archaeal monoglucosylarchaeol synthase recognized the stereostructure of the lipid substrate.It was proposed from the above results that the polar lipids of pre-cells proposed by Wachtershauser at the stage before differentiation of Archaea and Bacteria had common and contemporary polar head groups shared by Archaea and Bacteria. Polar lipids with racemic core lipid and common polar groups were segregated into homochiral polar lipids carrying common polar groups. This was the cause of differentiation of Archaea and Bacteria. Homologous enzymes for phospholipid synthesis were carried over into both domains of organisms. Stereospecific glycolipid synthases would be developed after differentiation of Archaea and Bacteria. Less