Cyclopropane Synthetases and M.tuberculosis Pathogenesis

描述(申请人提供)：结核分枝杆菌感染仍然是一个主要的全球健康危机。控制这一流行病的多学科计划必须包括新的抗生素和有效的疫苗接种，但这两种治疗方案目前都不可用。大量的新近证据表明，结核分枝杆菌的细胞膜是一个重要的致病决定因素，因此细胞膜生物合成途径是一个有吸引力的治疗靶点。在这笔赠款的前一次授予期间收集的数据确定了霉菌酸甲基转移酶家族的生物合成功能和致病重要性，该酶家族用环丙烷环和甲基分支修饰结核分枝杆菌的霉菌酸。虽然失去PCAA会减弱结核分枝杆菌的毒力，但失去cmaA2和反式环丙烷化会导致超强毒力和加剧肉芽肿性炎症。虽然这些结果表明环丙烷化是一个重要的致病决定因素，但由于环丙烷化缺失对宿主的益处尚不清楚，这些结果并未明确建议将霉酚酸甲基转移酶作为抗生素开发的靶点。在这一应用中，我们提供了初步的数据，表明霉酚酸甲基转移酶作为一类酶对于体外缓慢生长的分枝杆菌的生存是必不可少的。卡介苗中cmaA2和mmaA3的基因消融是综合致死的，提示了这种脂质修饰的新的生理作用。此外，我们还发现，大肠杆菌环丙烷脂肪酸合成酶的化学抑制剂可以抑制霉菌酸环丙烷化的多种途径，并在相同浓度下抑制分枝杆菌的生长。这些结果表明，霉酚酸甲基转移酶具有以前未知的基本功能，化学抑制这类酶可能是结核分枝杆菌药物开发的一个有吸引力的策略。在这项应用中，我们将以这些发现为基础，使用遗传学和生物化学来证实霉菌酸甲基转移酶作为抗生素开发的目标，并了解环丙烷化在缓慢生长的分枝杆菌中的重要作用。公共卫生相关性：该项目试图了解一系列脂质修饰酶(霉菌酸环丙烷合成酶)在结核分枝杆菌中的功能，结核分枝杆菌是结核病的病原菌。结核病是一个主要的全球健康问题，迫切需要新的抗生素来治疗这种感染。本申请中的实验旨在验证该酶家族作为抗生素开发的目标，并了解它们在致病中的作用。

DESCRIPTION (provided by applicant): Mycobacterium tuberculosis infection remains a major global health crisis. A multidisciplinary plan to control this epidemic must include new antibiotics and effective vaccination, but both of these therapeutic options are not presently available. Abundant recent evidence has implicated the M. tuberculosis cell envelope as an important pathogenesis determinant and therefore cell envelope biosynthetic pathways are an attractive therapeutic target. Data gathered during the prior award period of this grant defined the biosynthetic function and pathogenic importance of the mycolic acid methyltransferase enzyme family which modify the mycolic acids of M. tuberculosis with cyclopropane rings and methyl branches. Whereas loss of pcaA attenuates Mtb virulence, loss of cmaA2 and trans cyclopropanation causes hypervirulence and exacerbated granulomatous inflammation. While these results implicate cyclopropanation as an important pathogenesis determinant, they do not clearly recommend mycolic acid methyltransferase as a target for antibiotic development due to the unclear benefit to the host of loss of cyclopropanation. In this application we present preliminary data indicating that mycolic acid methyltransferases as an enzyme class are essential for slow growing mycobacterial viability in vitro. Genetic ablation of cmaA2 and mmaA3 in M. bovis BCG is synthetically lethal, suggesting a novel physiologic role for this lipid modification. Furthermore, we show that a chemical inhibitor of E. coli cyclopropane fatty acid synthase inhibits multiple pathways of mycolic acid cyclopropanation and inhibits mycobacterial growth at the same concentration. These results indicate that mycolic acid methyltransferases have a previously unrecognized essential function and that chemical inhibition of this enzyme class may be an attractive strategy for M. tuberculosis drug development. In this application we will build on these findings using genetics and biochemistry to substantiate mycolic acid methyltransferases as a target for antibiotic development and to understand the essential role of cyclopropanation in slow growing mycobacteria. PUBLIC HEALTH RELEVANCE: This project seeks to understand the function of a family of lipid modifying enzymes (mycolic acid cyclopropane synthases) in Mycobacterium tuberculosis, the causative bacterium of the disease Tuberculosis. Tuberculosis is a major global health problem and there is an urgent need for new antibiotics to treat this infection. The experiments in this application are designed to validate this enzyme family as a target for antibiotic development and to understand their role in causing disease.