Regulation of lipid biosynthesis in Mycobacterium tuberculosis

描述（由申请人提供）：结核分枝杆菌具有一种细胞包膜，这种包膜有助于这种细菌对许多抗生素的先天抗性，以及它引起疾病（结核病）和在宿主免疫反应存在下存活的能力。这个包膜由霉菌酸-阿拉伯半乳糖-肽聚糖（mAGP）细胞壁核心组成，其中霉菌酸朝向细胞表面。此外，脂质和脂聚糖的外层与mAGP的共价连接的霉菌酸形成双分子层。我们最近对豚鼠肺感染期间结核分枝杆菌产生的脂质和霉菌酸的研究表明，与体外培养的结核分枝杆菌相比，其脂质谱发生了巨大变化。两种细胞包膜产物，邻苯二酚二真菌酸（PDIM）和霉菌酸在体内生长过程中产生时发生了实质性的改变，并且已知两者都有助于发病。具体而言，PDIM的霉菌酸长度显著增加；1-、酮-和甲氧基霉菌酸的比例发生了变化，使得以前未被识别的结核分枝杆菌1-霉菌酸的形式成为体内生长的杆菌中主要的霉菌酸种类。固定相体外培养结核分枝杆菌在体内产生类似PDIMs的产物，但在体内不产生类似霉菌酸的产物。这些数据表明这两种细胞包膜产物的生物合成有不同的调控。了解改变PDIM和霉菌酸体内特征的基本调控事件，将有助于未来针对“体内”脂质结构在宿主-病原体相互作用中的作用进行研究。对这些调节机制的操纵也将允许开发方法来筛选潜在的抗结核药物，以对抗具有更准确地代表体内细菌的表型的细胞。本R21申请将提供控制霉菌酸链长度的调控机制的信息（Specific Aim 1）；并且负责在体外和体内霉菌酸谱之间的转变（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). PUBLIC HEALTH RELEVANCE: The proposed research will provide data to define mechanism responsible for regulating lipid biosynthesis in the bacterium (Mycobacterium tuberculosis) that causes tuberculosis. This information will allow future studies to elucidate how M. tuberculosis lipids interact with cells of the infected human host, and will allow for the development of more reliable screens to identify new anti-tuberculosis drugs.