Maranha Ana, Moynihan Patrick J, Miranda Vanessa, Correia Lourenço Eva, Nunes-Costa Daniela, Fraga Joana S, José Barbosa Pereira Pedro, Macedo-Ribeiro Sandra, Ventura M Rita, Clarke Anthony J, Empadinhas Nuno
CNC - Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal.
Department of Molecular and Cellular Biology, University of Guelph, Ontario, Canada.
Sci Rep. 2015 Sep 1;5:13610. doi: 10.1038/srep13610.
Mycobacteria synthesize unique intracellular methylglucose lipopolysaccharides (MGLP) proposed to modulate fatty acid metabolism. In addition to the partial esterification of glucose or methylglucose units with short-chain fatty acids, octanoate was invariably detected on the MGLP reducing end. We have identified a novel sugar octanoyltransferase (OctT) that efficiently transfers octanoate to glucosylglycerate (GG) and diglucosylglycerate (DGG), the earliest intermediates in MGLP biosynthesis. Enzymatic studies, synthetic chemistry, NMR spectroscopy and mass spectrometry approaches suggest that, in contrast to the prevailing consensus, octanoate is not esterified to the primary hydroxyl group of glycerate but instead to the C6 OH of the second glucose in DGG. These observations raise important new questions about the MGLP reducing end architecture and about subsequent biosynthetic steps. Functional characterization of this unique octanoyltransferase, whose gene has been proposed to be essential for M. tuberculosis growth, adds new insights into a vital mycobacterial pathway, which may inspire new drug discovery strategies.
分枝杆菌合成独特的细胞内甲基葡萄糖脂多糖（MGLP），据推测其可调节脂肪酸代谢。除了葡萄糖或甲基葡萄糖单元与短链脂肪酸发生部分酯化反应外，在MGLP还原端总是能检测到辛酸。我们鉴定出一种新型的糖辛酰基转移酶（OctT），它能有效地将辛酸转移至葡糖甘油酸（GG）和二葡糖甘油酸（DGG），这两种物质是MGLP生物合成过程中最早的中间体。酶学研究、合成化学、核磁共振光谱和质谱方法表明，与普遍观点相反，辛酸不是酯化到甘油酸的伯羟基上，而是酯化到DGG中第二个葡萄糖的C6羟基上。这些观察结果对MGLP还原端结构以及后续生物合成步骤提出了重要的新问题。这种独特的辛酰基转移酶的功能特性（其基因被认为对结核分枝杆菌的生长至关重要）为一条重要的分枝杆菌途径提供了新的见解，这可能会激发新的药物发现策略。
