School of Biosciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom.
PLoS One. 2012;7(10):e48211. doi: 10.1371/journal.pone.0048211. Epub 2012 Oct 31.
The biosynthesis of mycobacterial mannose-containing lipoglycans, such as lipomannan (LM) and the immunomodulator lipoarabinomanan (LAM), is carried out by the GT-C superfamily of glycosyltransferases that require polyprenylphosphate-based mannose (PPM) as a sugar donor. The essentiality of lipoglycan synthesis for growth makes the glycosyltransferase that synthesizes PPM, a potential drug target in Mycobacterium tuberculosis, the causative agent of tuberculosis. In M. tuberculosis, PPM has been shown to be synthesized by Ppm1 in enzymatic assays. However, genetic evidence for its essentiality and in vivo role in LM/LAM and PPM biosynthesis is lacking. In this study, we demonstrate that MSMEG3859, a Mycobacterium smegmatis gene encoding the homologue of the catalytic domain of M. tuberculosis Ppm1, is essential for survival. Depletion of MSMEG3859 in a conditional mutant of M. smegmatis resulted in the loss of higher order phosphatidyl-myo-inositol mannosides (PIMs) and lipomannan. We were also able to demonstrate that two other M. tuberculosis genes encoding glycosyltransferases that either had been shown to possess PPM synthase activity (Rv3779), or were involved in synthesizing similar polyprenol-linked donors (ppgS), were unable to compensate for the loss of MSMEG3859 in the conditional mutant.
分枝杆菌含有甘露糖的糖脂的生物合成，如脂阿拉伯甘露聚糖（LAM）和免疫调节剂脂甘露聚糖（LAM），由 GT-C 糖基转移酶家族完成，该家族需要多萜醇磷酸酯基甘露糖（PPM）作为糖供体。糖脂合成对生长的必要性使得合成 PPM 的糖基转移酶成为结核分枝杆菌（导致结核病的病原体）的潜在药物靶点。在结核分枝杆菌中，已经在酶促测定中显示 PPM 由 Ppm1 合成。然而，其在 LM/LAM 和 PPM 生物合成中的必需性和体内作用的遗传证据是缺乏的。在这项研究中，我们证明了 MSMEG3859，一种编码结核分枝杆菌 Ppm1 催化结构域同源物的分枝杆菌 smegmatis 基因，是生存所必需的。在分枝杆菌 smegmatis 的条件突变体中耗尽 MSMEG3859 导致更高阶的磷脂酰肌醇甘露糖苷（PIMs）和脂甘露聚糖的丢失。我们还能够证明，另外两个编码糖基转移酶的结核分枝杆菌基因，要么已经显示出具有 PPM 合酶活性（Rv3779），要么参与合成类似的多萜醇连接供体（ppgS），无法补偿条件突变体中 MSMEG3859 的缺失。
