Hacker Stephanie, Sohlenkamp Christian, Aktas Meriyem, Geiger Otto, Narberhaus Franz
Lehrstuhl für Biologie der Mikroorganismen, Ruhr-Universität Bochum, NDEF 06/783, D-44780 Bochum, Germany.
J Bacteriol. 2008 Jan;190(2):571-80. doi: 10.1128/JB.01423-07. Epub 2007 Nov 9.
Phosphatidylcholine (PC) is the major phospholipid in eukaryotic membranes. In contrast, it is found in only a few prokaryotes including members of the family Rhizobiaceae. In these bacteria, PC is required for pathogenic and symbiotic plant-microbe interactions, as shown for Agrobacterium tumefaciens and Bradyrhizobium japonicum. At least two different phospholipid N-methyltransferases (PmtA and PmtX) have been postulated to convert phosphatidylethanolamine (PE) to PC in B. japonicum by three consecutive methylation reactions. However, apart from the known PmtA enzyme, we identified and characterized three additional pmt genes (pmtX1, pmtX3, and pmtX4), which can be functionally expressed in Escherichia coli, showing different substrate specificities. B. japonicum expressed only two of these pmt genes (pmtA and pmtX1) under all conditions tested. PmtA predominantly converts PE to monomethyl PE, whereas PmtX1 carries out both subsequent methylation steps. B. japonicum is the first bacterium known to use two functionally different Pmts. It also expresses a PC synthase, which produces PC via condensation of CDP-diacylglycerol and choline. Our study shows that PC biosynthesis in bacteria can be much more complex than previously anticipated.
磷脂酰胆碱（PC）是真核细胞膜中的主要磷脂。相比之下，它仅在少数原核生物中发现，包括根瘤菌科的成员。在这些细菌中，PC对于致病性和共生性植物 - 微生物相互作用是必需的，如根癌土壤杆菌和日本慢生根瘤菌所示。据推测，在日本慢生根瘤菌中，至少有两种不同的磷脂N - 甲基转移酶（PmtA和PmtX）通过三个连续的甲基化反应将磷脂酰乙醇胺（PE）转化为PC。然而，除了已知的PmtA酶外，我们还鉴定并表征了另外三个pmt基因（pmtX1、pmtX3和pmtX4），它们可以在大肠杆菌中功能性表达，表现出不同的底物特异性。在所有测试条件下，日本慢生根瘤菌仅表达其中两个pmt基因（pmtA和pmtX1）。PmtA主要将PE转化为单甲基PE，而PmtX1进行后续的两个甲基化步骤。日本慢生根瘤菌是已知的第一种使用两种功能不同的Pmt的细菌。它还表达一种PC合酶，该酶通过CDP - 二酰甘油和胆碱的缩合产生PC。我们的研究表明，细菌中的PC生物合成可能比以前预期的要复杂得多。
