The biosynthesis of Mycobactin T, a virulence factor from Mycobacterium tuberculosis.

结核分枝杆菌是结核的病原体。异烟肼导致结核病死亡率急剧持续下降。这导致1988年的医学文献将其描述为一种正在消失的疾病，现在很容易治疗。然而，艾滋病毒的出现和耐多药结核分枝杆菌的迅速增加导致了巨大的变化。艾滋病毒感染者每年发展为活动性结核病的风险为7%，而免疫能力正常的人一生中患活动性结核病的风险为10%。同样，结核分枝杆菌耐药菌株在包括东南亚在内的许多地区的流行率超过5%。分枝杆菌感染被认为是全世界发病率和死亡率的主要原因，世卫组织估计，今后十年将有3000万人死于这些感染。显然，需要新的药物来对抗这种有机体日益增长的威胁。该项目的目的是详细介绍结核分枝杆菌产生菌素T的独特代谢途径，这对这种生物体的毒力至关重要。分枝杆菌素T帮助细菌获得铁，一种必需的营养物质。这些因素使分枝杆菌作用途径成为理想的药物靶点，了解其生物化学对于最终利用其干预结核分枝杆菌感染至关重要。我们假设它可能已经提供了临床使用的抗结核药物对氨基水杨酸酯（PAS）的未知作用位点。本项目将i)全面定义mycoblactin T的结构；Ii)克隆并过表达催化mycobactin形成前三步的关键基因；Iii)纯化和表征过表达蛋白的生化功能；iv)检查PAS与这种抗细菌药物可能靶向的蛋白质的相互作用。本研究结果将为今后抗结核药物的开发提供依据。

Mycobacterium tuberculosis is the causative agent of tuberculosis. The drug isoniazid led to a dramatic and sustained decline in mortality due to tuberculosis. This led to it being described in medical literature in 1988 as a disappearing disease which was now fairly easy to treat. However, the advent of HIV and the rapid rise of multidrug resistant M. tuberculosis led to dramatic changes. The risk that an HIV infected individual will develop active tuberculosis is 7% per year, compared to a lifetime risk of 10% for an immunocompetent person. Similarly, the prevalence of drug resistant strains of M. tuberculosis is over 5% in many regions, including SE asia. Mycobacterial infections are regarded as the leading cause of morbidity and mortality world wide and WHO estimates that 30 million deaths will occur in the next decade due to these infections. Clearly, new drugs are required to combat the rising menace of this organism. The aim of this project is to detail the unique metabolic pathways in M. tuberculosis that produce Mycobactin T, essential to the virulence of this organism. Mycobactin T helps the bacteria obtain iron, an essential nutrient. These factors make the mycobaction pathway an ideal drug target and an understanding of its biochemistry is essential to its eventual exploitation for intervention in M. tuberculosis infections. We hypothesise that it may already provide the unknown site of action of a clinically employed, antituberculosis drug para-aminosalicylate (PAS). This project will i) fully define the structure of mycobactin T; ii) clone and overexpress key genes which catalyse the first three steps of mycobactin formation; iii) purify and characterise the overexpressed proteins with respect to their biochemical function; iv) examine the interaction of PAS with the proteins likely to be targeted by this antimycobacterial agent. The results of this work will provide the basis for the development of future anti-tuberculosis drugs.