Assembly and export of mycobacterial lipoglycans

摘要 磷脂酰肌醇甘露糖苷(PIM)及其多糖基化产物脂甘露聚糖(LM)和 脂阿拉伯甘露聚糖(LAM)是一种复杂的糖脂和脂多糖，存在于所有 分枝杆菌属。它们在分枝杆菌生理学中扮演着各种基本的角色，尽管还没有明确的定义。 是结核病和麻风病程中重要的免疫调节分子，也是关键 促进分枝杆菌进入并在吞噬细胞和非吞噬细胞内存活的配体。 尽管在过去的25年里，在阐明结构和生物合成方面取得了很大的进展 在这些分子中，基本的问题仍然是导致它们生物合成和 移位到细胞表面。此外，虽然纯化后的多效性生物活性 细胞模型中的PIM、LM和LAM表明它们在发病机制中发挥着重要作用，研究旨在 验证这一假设并准确地描绘出它们对宿主-病原体相互作用的贡献 由完整的杆菌携带的细菌仍然受到缺乏突变株的限制 这些分子的生物合成和输出是可用的。 我们建议继续进行结构、遗传和生化研究，以期对结构做出完整的定义 (目标1)、生物合成(目标2)和出口(目标3)。完成了我们对PIM的理解， LM和LAM生物发生学，除了提供关于生物化学的基础知识 结核分枝杆菌(Mtb)有望导致必要的酶和转运蛋白的发现 就像emb家族的阿拉伯糖基转移酶和同向异构酶Dpre1一样，它可以提供新的 抗结核药物开发的机遇。积累重组菌种的可用性 结构上定义的生物合成前体将有助于结构-功能关系的研究，以及 在PIM、LM和LAM合成的各个方面存在缺陷的确定的Mtb突变体将允许精确的 评估这些分子在结核病免疫发病机制中的作用。 缩写： AG，阿拉伯半乳糖；AM，阿拉伯甘露聚糖；酰基T，酰基转移酶；arf，阿拉伯呋喃葡萄糖；arat，阿拉伯糖基转移酶；CZE，毛细管 区带电泳；DOC，脱氧胆酸；GT，糖基转移酶；INO，肌醇；LAM，脂阿拉伯甘露聚糖；LM，脂甘露聚糖；脂多糖， 脂多糖；MALDI-TOF，基质辅助激光解吸/电离飞行时间；甘露糖，甘露糖； 甘露糖基转移酶；MPI，甘露糖化磷脂酰肌醇；MS，质谱学；MTX，甲基硫代木糖；开放阅读 框架；OM，外膜；PIM，磷脂酰肌醇甘露糖苷；TLC，薄层层析。 命名法： PIM用于描述磷脂酰肌醇甘露糖苷的全球家族，其携带一到四种脂肪酸(附着于甘油， 肌醇和/或甘露糖)和一至六个甘露糖残基。在AcXPIMY中，x是指酯化为可用的酰基的数目 甘露糖或肌醇残基上的羟基，y是指甘露糖残基的数量；例如，Ac1PIM1对应于 磷脂酰肌醇-单甘露糖苷PIM1，带有两个与甘油(甘油二酯取代基)相连的酰基和一个 酯化为甘露糖残基的酰基。

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.