Biogenesis of lipoarabinomannan in mycobacteria

磷脂酰肌醇甘露糖苷（PIM）及其多糖基化对应物脂甘露聚糖（LM）和脂阿拉伯甘露聚糖（LAM）是在所有分枝杆菌物种的包膜中发现的复杂糖脂和脂聚糖。它们在分枝杆菌生理学中发挥各种基本但定义不明确的作用，是结核病和麻风病过程中重要的免疫调节分子，也是促进分枝杆菌进入吞噬细胞和非吞噬细胞的关键配体。虽然在过去的20年里，在阐明这些分子的结构方面取得了很大进展，但对导致其生物合成、组装和运输到细胞表面的途径的了解仍然不完整。这些途径的阐明，除了提供有关结核分枝杆菌生物化学的基础知识，预计将导致发现的基本酶和转运蛋白，可能代表新的抗结核药物的有趣的目标。积累这些分子的生物合成前体的重组分枝杆菌菌株的可用性将有助于结构-功能关系的研究和确定的分枝杆菌。在PIM、LM和LAM合成的各个方面缺陷的结核病突变体将允许精确评估这些分子对体内结核病免疫发病机制的贡献。在生物信息学，遗传学和生物化学的形式的综合方法之后，我们建议继续我们的工作，对参与PIM，LM和LAM的延伸和组装的酶的鉴定和功能表征，并进一步将这项工作扩展到负责生物合成中间体和最终产物跨细胞包膜的不同层的易位的转运蛋白的表征。缩略语：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; ESI，电喷雾电离; GT，糖基转移酶; LAM，脂阿拉伯甘露聚糖; LM，脂甘露聚糖; 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; myo-Ins，肌醇; ORF，开放阅读框;研究者，磷脂酰-肌肌醇; PIM，磷脂酰肌醇甘露糖苷; TFA，三氟乙酸; TLC，薄层色谱法。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1至4个脂肪酸（连接至甘油、肌醇和/或甘露糖）和1至6个甘露糖残基。在AcXPIMY中，x是指与甘露糖或肌醇残基上的可用羟基酯化的酰基的数目，y是指甘露糖残基的数目;例如，Ac 1 PIM 1对应于磷脂酰肌醇单甘露糖苷PIM 1，其携带两个与甘油连接的酰基（二酰基甘油取代基）和一个与甘露糖残基酯化的酰基。

DESCRIPTION (provided by applicant): Biogenesis of lipoarabinomannan in mycobacteria Summary Phosphatidylinositol mannosides (PIM) and their multiglycosylated counterparts, lipomannan (LM) and lipoarabinomannan (LAM) are complex glycolipids and lipoglycans found in the 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 into phagocytic and non-phagocytic cells. Although much progress has been made over the last 20 years in elucidating the structures of these molecules, knowledge of the pathways leading to their biosynthesis, assembling and transport to the cell surface is still incomplete. The elucidation of these pathways, in addition to providing fundamental knowledge about the biochemistry of Mycobacterium tuberculosis, is expected to lead to the discovery of essential enzymes and transporters that could represent interesting targets for novel anti-TB drugs. The availability of recombinant mycobacterial strains accumulating biosynthetic precursors of these molecules would facilitate structure-function relationship studies and that of defined M. tuberculosis mutants deficient in various aspects of PIM, LM and LAM synthesis would allow a precise assessment of the contribution of these molecules to the immunopathogenesis of tuberculosis in vivo. Following an integrated approach in the form of bioinformatics, genetics and biochemistry, we propose to pursue our work on the identification and functional characterization of the enzymes involved in the elongation and assembling of PIM, LM and LAM and to further extend this work to the characterization of the transporters responsible for the translocation of biosynthetic intermediates and end products across the different layers of the cell envelope. Abbreviations: AM, arabinomannan; AcylT, acyltransferase; Araf, arabinofuranosyl; AraT, arabinosyltransferase; CZE, capillary zone electrophoresis; DOC, deoxycholate; ESI, electrospray ionization; GT, glycosyltransferase; LAM, lipoarabinomannan; LM, lipomannan; MALDI-TOF, Matrix-Assisted Laser desorption/ionization time of flight; Manp, mannopyranosyl; ManT, mannosyltransferase; MPI, mannosylated phosphatidylinositol; MS, mass spectrometry; myo-Ins, myo-inositol; ORF, open reading frame; investigator, phosphatidyl-myo-inositol; PIM, phosphatidyl-myo-inositol mannosides; TFA, trifluoroacetic acid; 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.