Mutations in pimE restore lipoarabinomannan synthesis and growth in a Mycobacterium smegmatis lpqW mutant
Mutations in pimE restore lipoarabinomannan synthesis and growth in a Mycobacterium smegmatis lpqW mutant
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DOI：
10.1128/jb.00200-08
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发表时间：
2008-05-01
影响因子：
3.2
通讯作者：
Coppell, Ross L.
中科院分区：
文献类型：
--
作者：
Crellin, Paul K.;Kovacevic, Svetozar;Coppell, Ross L.
阿拉伯糖甘露聚糖脂（LAM）和磷脂酰肌醇甘露糖苷（PIM）是所有棒状杆菌和分枝杆菌（包括毁灭性的人类病原体结核分枝杆菌）细胞壁中丰富的糖脂。我们最近证明了M.脂蛋白编码基因lpqW的smeglobulin突变体在LAM生物合成中具有严重缺陷。当这些突变体在复杂培养基中培养时，自发旁路突变体一致地进化，其中LAM生物合成以极性PIM合成为代价恢复。在这里，我们表明，LAM的生物合成的lpqW突变体的结果从pimE基因的二次突变的恢复。PimE是一种甘露糖基转移酶，参与将AcPIM 4转化为极性更强的PIM，AcPIM 4是PIM和LAM生物合成途径中提出的分支点中间体。pimE的突变是由于插入了移动的遗传元件ISMsm1和独立的点突变，这些点突变聚集在该多位膜蛋白的预测胞质外环中。我们的研究结果提供了第一个强有力的证据，即LpqW是必需的通道中间体，如AcPIM 4进入LAM合成和PimE功能的损失导致积累的AcPIM 4，绕过LpqW的需要。这些数据突出了调节这些基本细胞壁组分的生物合成途径的新机制。
Lipoarabinomarmans (LAMs) and phosphatidylinositol mannosides (PIMs) are abundant glycolipids in the cell walls of all corynebacteria and mycobacteria, including the devastating human pathogen Mycobacterium tuberculosis. We have recently shown that M. smegmatis mutants of the lipoprotein-encoding lpqW gene have a profound defect in LAM biosynthesis. When these mutants are cultured in complex medium, spontaneous bypass mutants consistently evolve in which LAM biosynthesis is restored at the expense of polar PIM synthesis. Here we show that restoration of LAM biosynthesis in the lpqW mutant results from secondary mutations in the pimE gene. PimE is a mannosyltransferase involved in converting AcPIM4, a proposed branch point intermediate in the PIM and LAM biosynthetic pathways, to more polar PIMs. Mutations in pimE arose due to insertion of the mobile genetic element ISMsm1 and independent point mutations that were clustered in predicted extracytoplasmic loops of this polytopic membrane protein. Our findings provide the first strong evidence that LpqW is required to channel intermediates such as AcPIM4 into LAM synthesis and that loss of PimE function results in the accumulation of AcPIM4, bypassing the need for LpqW. These data highlight new mechanisms regulating the biosynthetic pathways of these essential cell wall components.