Wilderman Paula J, Vasil Adriana I, Martin Wesley E, Murphy Robert C, Vasil Michael L
Department of Microbiology, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, Denver, CO 80262, USA.
J Bacteriol. 2002 Sep;184(17):4792-9. doi: 10.1128/JB.184.17.4792-4799.2002.
Phosphatidylcholine (PC) is a ubiquitous membrane lipid in eukaryotes but has been found in only a limited number of prokaryotes. Both eukaryotes and prokaryotes synthesize PC by methylating phosphatidylethanolamine (PE) by use of a phospholipid methyltransferase (Pmt). Eukaryotes can synthesize PC by the activation of choline to form choline phosphate and then CDP-choline. The CDP-choline then condenses with diacylglycerol (DAG) to form PC. In contrast, prokaryotes condense choline directly with CDP-DAG by use of the enzyme PC synthase (Pcs). PmtA was the first enzyme identified in prokaryotes that catalyzes the synthesis of PC, and Pcs in Sinorhizobium meliloti was characterized. The completed release of the Pseudomonas aeruginosa PAO1 genomic sequence contains on open reading frame predicted to encode a protein that is highly homologous (35% identity, 54% similarity) to PmtA from Rhodobacter sphaeroides. Moreover, the P. aeruginosa PAO1 genome encodes a protein with significant homology (39% amino acid identity) to Pcs of S. meliloti. Both the pcs and pmtA homologues were cloned from PAO1, and homologous sequences were found in almost all of the P. aeruginosa strains examined. Although the pathway for synthesizing PC by use of Pcs is functional in P. aeruginosa, it does not appear that this organism uses the PmtA pathway for PC synthesis. We demonstrate that the PC synthesized by P. aeruginosa PAO1 localized to both the inner and outer membranes, where it is readily accessible to its periplasmic, PC-specific phospholipase D.
磷脂酰胆碱（PC）是真核生物中普遍存在的膜脂，但仅在少数原核生物中被发现。真核生物和原核生物都通过使用磷脂甲基转移酶（Pmt）将磷脂酰乙醇胺（PE）甲基化来合成PC。真核生物可以通过激活胆碱形成磷酸胆碱，然后形成CDP - 胆碱来合成PC。CDP - 胆碱随后与二酰甘油（DAG）缩合形成PC。相比之下，原核生物通过使用PC合酶（Pcs）将胆碱直接与CDP - DAG缩合。PmtA是在原核生物中鉴定出的第一种催化PC合成的酶，并且对苜蓿中华根瘤菌中的Pcs进行了表征。铜绿假单胞菌PAO1基因组序列的完整发布包含一个开放阅读框，预测该框编码一种与球形红杆菌的PmtA高度同源（35% 同一性，54% 相似性）的蛋白质。此外，铜绿假单胞菌PAO1基因组编码一种与苜蓿中华根瘤菌的Pcs具有显著同源性（39% 氨基酸同一性）的蛋白质。pcs和pmtA同源物均从PAO1中克隆出来，并且在几乎所有检测的铜绿假单胞菌菌株中都发现了同源序列。尽管通过使用Pcs合成PC的途径在铜绿假单胞菌中起作用，但该生物体似乎并未使用PmtA途径进行PC合成。我们证明，铜绿假单胞菌PAO1合成的PC定位于内膜和外膜，在那里其周质PC特异性磷脂酶D很容易接近它。
