Protein Secretion Pathways of Mycobacterium tuberculosis

描述（由申请人提供）：每年有200多万人死于结核病，据信世界上三分之一的人口感染了导致这种疾病的结核分枝杆菌。为了开发新的结核病药物和疫苗，需要对结核分枝杆菌的生理和发病机制有一个全面的了解。蛋白质分泌途径在细菌发病机制中起重要作用。本研究的长期目标是确定分枝杆菌的蛋白质输出系统及其在结核分枝杆菌发病机制中的作用。分枝杆菌罕见地具有两个SecA同源物（SecA1和SecA2）。SecA在整个细菌中高度保守，是一般Sec依赖转运途径的核心组成部分，该途径输出含有氨基末端Sec信号序列的蛋白质。在分枝杆菌中，SecA1是必需的“管家”SecA，而SecA2是非必需的辅助分泌因子。在结核分枝杆菌中，secA2基因的缺失降低了该有机体在小鼠中的毒力。提示SecA2输出结核分枝杆菌毒力因子。研究人员发现结核分枝杆菌的两种抗氧化剂通过依赖seca2的出口途径分泌。这导致假设SecA2是结核分枝杆菌逃避宿主氧化攻击的毒力机制的一部分。这两种抗氧化剂都缺乏Sec信号序列，其输出的机制基础尚不清楚。该研究将描述SecA2在发病机制和蛋白质输出中的作用。本研究的具体目的如下：(1)通过在巨噬细胞和小鼠中检测结核分枝杆菌AsecA2突变体及其抗氧化攻击的能力，研究SecA2和分泌抗氧化剂在结核分枝杆菌发病机制中的作用；(2)鉴定由SecA2输出的蛋白质；(3)通过鉴定与SecA2作用的其他蛋白质，表征SecA2在蛋白质输出中的功能基础。这项研究将扩大我们对结核分枝杆菌毒力蛋白和结核分枝杆菌蛋白分泌途径的理解。它也可能有助于阐明活性氧在宿主对结核分枝杆菌反应中的作用。这项研究有可能促进新的抗结核战略的发展。

DESCRIPTION (provided by applicant): More than two million people die each year from tuberculosis and one third of the world' s population is believed infected with Mycobacterium tuberculosis, the bacterium responsible for this disease. To enable development of new drugs and vaccines for tuberculosis, a thorough understanding of M. tuberculosis physiology and pathogenesis is required. Protein secretion pathways play an important role in bacterial pathogenesis. The long-term objective of this research is to define the protein export systems of mycobacteria and the role they play in M. tuberculosis pathogenesis. Mycobacteria are unusual in possessing two SecA homologues (SecA1 and SecA2). SecA is highly conserved throughout bacteria and is a central component of the general Sec-dependent transport pathway, which exports proteins containing amino-terminal Sec signal sequences. In mycobacteria, SecA1 is the essential "housekeeping" SecA while SecA2 is a non-essential accessory secretion factor. A deletion of the secA2 gene in M. tuberculosis attenuated the virulence of the organism in mice. This suggests that SecA2 exports virulence factors of M. tuberculosis. The investigators identified two antioxidants of M. tuberculosis as being secreted by a SecA2-dependent export pathway. This has led to the hypothesis that SecA2 is part of a virulence mechanism of M. tuberculosis to evade the oxidative attack of the host. Both of these antioxidants lack Sec signal sequences and the mechanistic basis of their export is unknown. The proposed research will characterize the roles of SecA2 in pathogenesis and in protein export. The specific aims of this proposal are the following: (1) Investigate the role of SecA2 and secreted antioxidants in M. tuberculosis pathogenesis by testing a AsecA2 mutant of M. tuberculosis in both macrophages and mice and in its ability to resist oxidative attack, (2) Identify proteins exported by SecA2, and (3) Characterize the basis of SecA2 function in protein export by identifying other proteins that act with SecA2. This study will expand our understanding of the proteins that contribute to M. tuberculosis virulence and the protein secretion pathways of M. tuberculosis. It may also help clarify the role of reactive oxygen species in the host response to M. tuberculosis. This research has the potential of facilitating development of new anti-tuberculosis strategies.