Assembly and export of mycobacterial lipoglycans

摘要 磷脂酰肌醇甘露糖苷（PIM）和它们的多糖基化对应物脂甘露聚糖（LM）以及 脂阿拉伯甘露聚糖（LAM）是在所有细胞的细胞包膜中发现的复杂糖脂和脂聚糖。 分枝杆菌物种。它们在分枝杆菌生理学中起着各种重要的作用，尽管定义不清 是结核病和麻风病发病过程中重要的免疫调节分子， 配体促进分枝杆菌的进入及其在吞噬细胞和非吞噬细胞内的存活。 虽然在过去的25年里，在阐明其结构和生物合成方面取得了很大进展， 在这些分子中，关于导致其生物合成的途径的基本问题仍然存在， 转运到细胞表面。此外，虽然纯化的蛋白质显示出多效性生物活性， 细胞模型中的PIM、LM和LAM表明它们在发病机制中起重要作用， 验证这一假设，并精确地描述它们对宿主-病原体相互作用的贡献， 由完整的杆菌携带的突变体仍然受到缺乏突变体的限制，突变体缺乏明确的方面， 生物合成和输出这些可用的分子。 我们建议进行结构、遗传和生化研究，以完整地定义结构 (Aim 1）、PIM、LM和LAM的生物合成（目标2）和输出（目标3）。完成我们对PIM的理解， LM和LAM的生物发生，除了提供有关生物化学的基本知识， 结核分枝杆菌（Mtb），有望导致发现必需的酶和转运蛋白 与Emb家族的阿拉伯糖基转移酶和差向异构酶DprE 1非常相似， 抗结核药物开发的机遇。重组菌株积累的可用性 结构确定的生物合成前体将促进结构-功能关系的研究， 定义的在PIM、LM和LAM合成的各个方面缺陷的Mtb突变体将允许精确的 评估这些分子对结核病免疫发病机制的贡献。 缩略语： AG，阿拉伯半乳聚糖; AM，阿拉伯甘露聚糖; AcylT，酰基转移酶; Araf，阿拉伯呋喃糖基; AraT，阿拉伯糖基转移酶; CZE，毛细管 区带电泳; DOC，脱氧胆酸盐; GT，糖基转移酶; Ino，肌醇; LAM，脂阿拉伯甘露聚糖; LM，脂甘露聚糖; LPS， 脂多糖; MALDI-TOF，基质辅助激光解吸/电离飞行时间; Manp，吡喃甘露糖基; ManT， 甘露糖基转移酶; MPI，甘露糖基化磷脂酰肌醇; MS，质谱法; MTX，甲硫基木糖; ORF，开放阅读 框架; OM，外膜; PIM，磷脂酰肌醇甘露糖苷; TLC，薄层色谱法。 名称： PIM用于描述磷脂酰肌醇甘露糖苷的全球家族，其携带一到四个脂肪酸（连接到甘油， 肌醇和/或甘露糖）和1至6个甘露糖残基。在AcXPIMY中，X是指酯化为可用的酰基的酰基数目。 y是指甘露糖残基的数目;例如，Ac 1 PIM 1对应于甘露糖残基上的羟基。 磷脂酰肌醇单甘露糖苷PIM 1携带两个酰基连接到甘油（二酰基甘油取代基）和一个酰基连接到甘油（二酰基甘油取代基）。 酯化到甘露糖残基上的酰基。

Abstract Phosphatidylinositol mannosides (PIM) and their multiglycosylated counterparts, lipomannan (LM) and lipoarabinomannan (LAM), are complex glycolipids and lipoglycans found in the cell envelopes of all mycobacterial species. They play various essential although poorly defined roles in mycobacterial physiology and are important immunomodulatory molecules in the course of tuberculosis and leprosy as well as key ligands promoting the entry of mycobacteria and their survival within phagocytic and non-phagocytic cells. Although much progress has been made over the last 25 years in elucidating the structures and biosynthesis of these molecules, fundamental questions remain about the pathways leading to their biosynthesis and translocation to the cell surface. Furthermore, while the pleiotropic biological activities displayed by purified PIM, LM and LAM in cellular models suggest that they play important roles in pathogenesis, studies aimed at validating this assumption and precisely delineating their contribution to host-pathogen interactions when carried by intact bacilli are still limited by the paucity of mutants deficient in well-defined aspects of the biosynthesis and export of these molecules that are available. We propose to pursue structural, genetic and biochemical studies toward a complete definition of the structure (Aim 1), biosynthesis (Aim 2) and export (Aim 3) of PIM, LM and LAM. Completing our understanding of PIM, LM and LAM biogenesis, in addition to providing fundamental knowledge about the biochemistry of Mycobacterium tuberculosis (Mtb), is expected to lead to the discovery of essential enzymes and transporters which, much like the arabinosyltransferases of the Emb family and the epimerase DprE1, could provide new opportunities for anti-tuberculosis drug development. The availability of recombinant strains accumulating structurally defined biosynthetic precursors will facilitate structure-function relationship studies, and that of defined Mtb mutants deficient in various aspects of PIM, LM and LAM synthesis will allow a precise assessment of the contribution of these molecules to the immunopathogenesis of tuberculosis. Abbreviations: AG, arabinogalactan; AM, arabinomannan; AcylT, acyltransferase; Araf, arabinofuranosyl; AraT, arabinosyltransferase; CZE, capillary zone electrophoresis; DOC, deoxycholate; GT, glycosyltransferase; Ino, myo-Inositol; LAM, lipoarabinomannan; LM, lipomannan; LPS, lipopolysaccharide; MALDI-TOF, Matrix-Assisted Laser desorption/ionization time of flight; Manp, mannopyranosyl; ManT, mannosyltransferase; MPI, mannosylated phosphatidylinositol; MS, mass spectrometry; MTX, methyl-thio-xylose; ORF, open reading frame; OM, outer membrane; PIM, phosphatidyl-myo-inositol mannosides; TLC, thin-layer chromatography. Nomenclature: PIM is used to describe the global family of phosphatidylinositol mannosides that carries one to four fatty acids (attached to the glycerol, inositol and/or mannose) and one to six mannose residues. In AcXPIMY, x refers to the number of acyl groups esterified to available hydroxyls on the mannose or myo-inositol residues, y refers to the number of mannose residues; e.g. Ac1PIM1 corresponds to the phosphatidylinositol mono-mannoside PIM1 carrying two acyl groups attached to the glycerol (the diacylglycerol substituent) and one acyl group esterified to the mannose residue.