Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, Toulouse, France.
Sci Rep. 2017 Aug 11;7(1):7913. doi: 10.1038/s41598-017-08489-7.
Protein O-mannosylation is crucial for the biology of Mycobacterium tuberculosis but the key mannosylated protein(s) involved and its(their) underlying function(s) remain unknown. Here, we demonstrated that the M. tuberculosis mutant (Δpmt) deficient for protein O-mannosylation exhibits enhanced release of lipoarabinomannan (LAM) in a complex with LprG, a lipoprotein required for LAM translocation to the cell surface. We determined that LprG is O-mannosylated at a unique threonine position by mass spectrometry analyses of the purified protein. However, although replacement of this amino acid by an alanine residue completely abolished LprG O-mannosylation, the increased release of the LAM/LprG complex was preserved. We found that the increased secretion of this complex is due to enhanced LAM production in the Δpmt M. tuberculosis and M. smegmatis mutants relative to their wild-type counterparts. This abnormal release of LAM/LprG has functional consequences on the induction of inflammatory responses and provides a possible explanation for the reduced virulence of the M. tuberculosis Δpmt mutant.
蛋白 O-甘露糖基化对于结核分枝杆菌的生物学至关重要，但涉及的关键甘露糖基化蛋白及其潜在功能仍不清楚。在这里，我们证明了缺乏蛋白 O-甘露糖基化的结核分枝杆菌突变体（Δpmt）在与脂蛋白 LprG 形成的复合物中表现出增强的脂阿拉伯甘露聚糖（LAM）释放，LprG 是将 LAM 转运到细胞表面所必需的脂蛋白。我们通过对纯化蛋白的质谱分析确定，LprG 在一个独特的苏氨酸位置被 O-甘露糖基化。然而，尽管用丙氨酸残基取代该氨基酸完全消除了 LprG 的 O-甘露糖基化，但 LAM/LprG 复合物的释放增加仍然得以保留。我们发现，这种复合物的分泌增加是由于与野生型相比，Δpmt 结核分枝杆菌和耻垢分枝杆菌突变体中 LAM 的产量增加。这种异常的 LAM/LprG 释放对诱导炎症反应具有功能后果，并为结核分枝杆菌 Δpmt 突变体的毒力降低提供了可能的解释。
