GENES FOR METHY1-BRANCHED WALL LIPIDS AND TUBERCULOSIS

结核病（TB）和与艾滋病相关的其他分枝杆菌感染的死灰复燃威胁着全世界的人类健康。耐药结核病的出现使得发现新的药物靶点变得至关重要。结核分枝杆菌的细胞壁含有多种不寻常的脂质，具有致病分枝杆菌所特有的多种类型的多甲基支链脂肪酸。这些脂质被认为在病原体抵抗抗菌剂和逃避宿主防御反应的能力中起重要作用。这些独特的含有多个甲基支链脂肪酸的脂质的生物合成可以为新的抗分枝杆菌药物提供理想的靶点。基因组测序显示，分枝杆菌基因组的一个显着独特的特征是，它包含了异常大量的基因参与脂质代谢。基于与分枝蜡酸合酶（MAS）的同源性，我们已经鉴定了两类聚酮化合物合酶（PKS）样基因，其含有活性位点结构域的完整补充，所述活性位点结构域应该参与催化合成多甲基支链脂肪酸所需的所有步骤：与mas高度同源的1类mas样基因mas样基因（ms 11、ms 12和ms 13）和显示出与mas较低程度同源性的2类mas样基因（ms 14、ms 15、ms 16和ms 17）。这些开放阅读框（ORF）最有可能编码在M中发现的八类以上的甲基支链脂肪酸。结核为了阐明这些基因的功能，并研究它们在寄主-病原体相互作用中的可能作用，我们提出以下具体目标：1）确定M.结核分枝杆菌表达的产物的特征。smegaltine，并通过测定其破坏的生化和功能后果。2)目的：研究M.结核基因组，通过表征其在M. smegaltine，并通过测定其破坏的生化和功能后果。3)确定由上述基因破坏引起的特定脂质缺乏是否影响宿主-病原体相互作用和毒力。这些结果将有助于确定对发病机制至关重要的细胞壁脂质，这些脂质可能是新的抗分枝杆菌药物的合适靶标。

Resurgence of tuberculosis (TB) and other mycobacterial infections associated with AIDS threaten human health world-wide. Emergence of drug resistant TB makes it critical to discover new drug targets. Cell walls of Mycobacterium tuberculosis contain a variety of unusual lipids with many types of multiple methyl-branched fatty acids that are unique to pathogenic mycobacteria. These lipids are thought to play important roles in the ability of the pathogens to resist antimicrobial agents and evade the defense reactions of the host. Biosynthesis of these unique lipids containing multiple methyl-branched fatty acids could offer ideal targets for new anti mycobacterial drugs. Genomic sequencing revealed that a remarkably unique feature of the mycobacterial genome is that it contains an unusually large number of genes involved in lipid metabolism. Based on the homology to mycocerosic acid synthase (mas) we have identified two classes of polyketide synthase (pks)-like genes which contain a full complement of active site domains that should be involved in the catalysis of all of the steps required for the synthesis of multimethyl- branched fatty acids: Class 1 mas-like genes mas-like genes (msl1, msl2 and msl3) that are highly homologous to mas and Class 2 (msl4m msl5, msl6 and msl7) which show a lesser degree of homology to mas. These open reading frames (ORFs) most probably encode the more than eight classes of methyl-branched fatty acids found in M. tuberculosis. To elucidate the function of these genes and to examine their possible role in the host-pathogen interaction, we propose to pursue the following specific aims: 1) Determine the functions of Class 1 mas-like genes, ms1, msl2 and msl3 of M. tuberculosis by characterization of their products expressed in M. smegmatis, and by determination of the biochemical and functional consequences of their disruption. 2) Determine the functions of Class 2 (msl4, msl5, msl6 and msl7) mas-like genes in M. tuberculosis genome, by characterization of their products expressed in M. smegmatis, and by determination of the biochemical and functional consequences of their disruption. 3) Determine whether lack of specific lipids caused by the above gene-disruptions affects host-pathogen interaction and virulence. The results will help identify cell wall lipids critical for pathogenesis that might be suitable targets for new anti-mycobacterial drugs.