Matsumoto K
Department of Biochemistry and Molecular Biology, Faculty of Science, Saitama University, 255 Shimo-ohkubo, Urawa, Saitama 338-8570, Japan.
Mol Microbiol. 2001 Mar;39(6):1427-33. doi: 10.1046/j.1365-2958.2001.02320.x.
The major anionic phospholipids of Escherichia coli, phosphatidylglycerol (PG) and cardiolipin (CL), have been considered to be indispensable for essential cellular functions, such as the initiation of DNA replication and translocation of proteins across the cytoplasmic membrane. However, we successfully constructed a null pgsA mutant of E. coli that had undetectable levels of PG and CL if the major outer membrane lipoprotein was deficient, clearly indicating that these anionic phospholipids are not indispensable. In the null mutant, we observed the accumulation of phosphatidic acid, an acidic biosynthetic precursor. This suggests a functionally substitutable nature of these anionic phospholipids and allows us to formulate a dual role model for the physiological roles of the anionic phospholipids in E. coli. The anionic phospholipids may play dual roles in E. coli as (i) substrates for head group-specific enzyme reactions, albeit the viability of null PG mutants indicates that the products of head group-specific reactions are not essential; and (ii) those that are replaceable, partly or entirely, by other phospholipids bearing net negative charges, because of their rather loose head group specificity. These two aspects of the physiological roles of anionic phospholipids are discussed with special reference to the phospholipids of other bacteria and eukaryotic organelles.
大肠杆菌的主要阴离子磷脂，磷脂酰甘油（PG）和心磷脂（CL），被认为对于诸如DNA复制起始和蛋白质跨细胞质膜转运等基本细胞功能是不可或缺的。然而，我们成功构建了大肠杆菌的pgsA基因缺失突变体，如果主要外膜脂蛋白缺乏，该突变体中PG和CL的水平检测不到，这清楚地表明这些阴离子磷脂并非不可或缺。在该基因缺失突变体中，我们观察到酸性生物合成前体磷脂酸的积累。这表明这些阴离子磷脂具有功能上的可替代性，使我们能够为大肠杆菌中阴离子磷脂的生理作用构建一个双重作用模型。阴离子磷脂在大肠杆菌中可能发挥双重作用：（i）作为特定头部基团酶反应的底物，尽管PG基因缺失突变体的存活能力表明特定头部基团反应的产物并非必需；（ii）由于其头部基团特异性相当宽松，部分或完全可被带有净负电荷的其他磷脂替代。本文特别参考其他细菌和真核细胞器的磷脂，讨论了阴离子磷脂生理作用的这两个方面。
