Regulation of lipid biosynthesis in Mycobacterium tuberculosis

描述(申请人提供)：结核分枝杆菌拥有一种细胞膜，有助于这种细菌对许多抗生素的先天抵抗力，以及它在宿主免疫反应存在的情况下致病(结核病)和存活的能力。该膜由菌丝酸-阿拉伯半乳糖-肽聚糖(MAGP)细胞壁核心组成，菌丝酸朝向细胞表面。此外，外层的脂类和脂多糖与mAGP的共价连接的真菌酸形成双层。我们最近对结核分枝杆菌在豚鼠肺感染过程中产生的脂类和真菌酸的研究表明，与体外培养的细菌相比，脂类分布发生了戏剧性的变化。在体内生长过程中产生的两种细胞被膜产物，即邻苯二甲酸二菌酯(PDIM)和真菌酸(Mycolic Acid)会发生很大的变化，这两种物质都是已知的致病因素。具体地说，PDIM的分枝杆菌酸的长度显著增加；1-，酮-和甲氧基真菌酸的比例发生变化，使得以前未被识别的结核分枝杆菌1-分枝杆菌成为体内培养的杆菌的主要真菌酸种类。结核分枝杆菌体外培养的固定相在体内产生类似于PDIMs，但在体内不产生类似于霉菌酸谱。这些数据显示了这两种细胞被膜产物生物合成的不同调控。了解改变PDIM和真菌酸在体内的分布的基本调节事件将有助于未来针对“体内”脂结构在宿主-病原体相互作用中的作用的研究。对这些调控机制的操作也将允许开发方法，以筛选针对表型更准确地代表体内细菌的细胞的潜在抗结核药物。在R21的应用中，我们将提供关于控制真菌酸链长度(特定目标1)的调节机制的信息；以及负责体外和体内真菌酸谱之间转换的调节机制(特定目标2)。

DESCRIPTION (provided by applicant): Mycobacterium tuberculosis possesses a cell envelope that contributes to this bacterium's innate resistance to many antibiotics, and its ability to cause disease (tuberculosis) and survive in the presence of the host's immune response. This envelope is comprised of the mycolic acid-arabinogalactan-peptidoglycan (mAGP) cell wall core where the mycolic acids are oriented toward the surface of the cell. Further, an outer layer of lipids and lipoglycans form a bilayer with the covalently linked mycolic acids of mAGP. Our recent studies of the lipids and mycolic acids produced by M. tuberculosis during infection of the guinea pig lung revealed a dramatic shift in the lipid profile as compared to that of the bacterium grown in vitro. Two cell envelope products, phthiocerol dimycocerosic acids (PDIM) and mycolic acids were substantially altered when produced during in vivo growth and both are known to contribute to pathogenesis. Specifically, the mycocerosic acids of the PDIM significantly increased in length; and the ratio of 1-, keto- and methoxymycolic acids shifted such that a previously unrecognized form of the M. tuberculosis 1-mycolate became the dominant mycolic acid species of in vivo grown bacilli. Stationary phase in vitro cultures of M. tuberculosis produced in vivo like PDIMs but not in vivo like mycolic acid profiles. These data demonstrated differential regulation in the biosynthesis of these two cell envelope products. Understanding the basic regulatory events that alter the in vivo profile of PDIM and mycolic acids will allow for future studies that target the role of "in vivo" lipid structures in host-pathogen interactions. Manipulation of these regulatory mechanisms also will allow for development of methods to screen potential anti-tuberculosis drugs against cells with a phenotype that more accurately represents the bacterium in vivo. This R21 application we will provide information on regulatory mechanisms that control mycocerosic acids chain length (Specific Aim 1); and that are responsible for the shift between in vitro and in vivo mycolic acid profiles (Specific Aim 2).