Riekhof Wayne R, Andre Carl, Benning Christoph
Department of Biochemistry and Molecular Biology , Michigan State University, East Lansing, MI 48824, USA.
Arch Biochem Biophys. 2005 Sep 1;441(1):96-105. doi: 10.1016/j.abb.2005.07.001.
Betaine lipids are non-phosphorous glycerolipid analogs of phosphatidylcholine. The biosynthesis of the betaine lipid diacylglyceryl-N,N,N-trimethylhomoserine has previously been studied in phosphate-starved cells of the purple bacterium Rhodobacter sphaeroides, and a genetic approach identified two proteins that are necessary for this process. Here, we show that all reactions of DGTS biosynthesis in R. sphaeroides are attributable to RsBtaA and RsBtaB, as co-expression of the respective genes leads to DGTS formation in Escherichia coli, which normally lacks this lipid. The recombinant RsBtaA protein was membrane-associated and showed S-adenosylmethionine/diacylglycerol 3-amino-3-carboxypropyl transferase activity. RsBtaA directed the transfer of label from 1-[(14)C]S-adenosylmethionine or [(14)C]diacylglycerol at equal rates into the betaine lipid precursor diacylglycerylhomoserine identifying both metabolites as the substrates of the reaction. Comparative analysis of RsBtaA and its bacterial orthologs revealed a motif with similarity to the AdoMet binding pocket of methyltransferases, and allowed the prediction of residues involved in substrate binding.
甜菜碱脂是磷脂酰胆碱的非磷甘油脂类似物。此前已在紫色细菌球形红杆菌的缺磷细胞中研究了甜菜碱脂二酰甘油 - N,N,N - 三甲基高丝氨酸的生物合成，并且一种遗传学方法鉴定出了该过程所需的两种蛋白质。在此，我们表明球形红杆菌中DGTS生物合成的所有反应都归因于RsBtaA和RsBtaB，因为各自基因的共表达导致在通常缺乏这种脂质的大肠杆菌中形成DGTS。重组RsBtaA蛋白与膜相关，并表现出S - 腺苷甲硫氨酸/二酰甘油3 - 氨基 - 3 - 羧丙基转移酶活性。RsBtaA以相等的速率将来自1 - [（14）C] S - 腺苷甲硫氨酸或[（14）C]二酰甘油的标记转移到甜菜碱脂前体二酰甘油高丝氨酸中，将这两种代谢物都鉴定为该反应的底物。对RsBtaA及其细菌直系同源物的比较分析揭示了一个与甲基转移酶的AdoMet结合口袋相似的基序，并允许预测参与底物结合的残基。
