The molecular mechanism of Legionella type IV secretion

描述(申请人提供)：嗜肺军团菌是一种革兰氏阴性细菌，在环境中的淡水阿米巴内复制，但也可通过在肺泡巨噬细胞内复制而导致人类军团病。嗜肺乳杆菌通过改变吞噬细胞的内吞途径，在正常杀菌的吞噬细胞内存活和复制，从而抑制吞噬小体-溶酶体的快速融合。嗜肺性乳杆菌通过IV型分泌系统(T4SS)向宿主体内注入大量毒力因子，从而扰乱宿主细胞的正常功能。嗜肺乳杆菌T4SS由26个Dot或ICM基因编码，在细菌细胞膜上编码一个大的大分子复合体。由于这一系统的复杂性，嗜肺性乳杆菌如何输出底物的分子机制仍未确定。然而，细菌分泌领域的最新进展提供了一种新的强大的技术，TRIP(易位免疫沉淀)，它允许详细了解T4SS的底物分泌。利用TRIP，不仅可以显示特定的Dot/LCM蛋白与易位底物相互作用，而且可以确定它们相互作用的时间。基于这一进展，我们的总体目标是了解Dot/LCM分泌系统是如何发挥作用的。这项研究将在两个方面与人类健康相关。首先，建立嗜肺乳杆菌在巨噬细胞内生存和复制的机制将提供对其如何致病的进一步了解，并可能揭示用于药物治疗的新靶点。其次，由于各种细菌病原体通常使用专门的分泌系统，因此关于嗜肺乳杆菌分泌器的知识可能适用于了解其他病原体使用的毒力分子机制，并可作为预防或治疗许多不同疾病的基础。

DESCRIPTION (provided by applicant): Legionella pneumophila is a Gram negative bacterium that replicates inside fresh water amoebae in the environment but can also cause Legionnaires' disease in humans by replicating inside alveolar macrophages. L. pneumophila survives and replicates inside normally bactericidal phagocytic cells by altering their endocytic pathway, thereby inhibiting rapid phagosome-lysosome fusion. L. pneumophila is able to perturb normal host cell function by injecting a large number of virulence factors into the host via a type IV secretion system (T4SS). The L. pneumophila T4SS is encoded by twenty six dot or icm genes, which encode a large macromolecular complex in the bacterial cell envelope. Due to the complexity of this system, the molecular mechanism of how L. pneumophila exports substrates has remained undetermined. However, a recent advance in the field of bacterial secretion has provided a new and powerful technique, TrIP (translocation immunoprecipitation), that allows a detailed understanding of substrate secretion by T4SSs. Using TrIP, not only can specific Dot/lcm proteins be shown to interact with a translocated substrate, but the timing of their interactions in relation to each other can be ascertained. Based on this advance, our overall goal is to understand how the Dot/lcm secretion system functions. This research will relate to human health in two ways. First, establishing the mechanism used by L. pneumophila to survive and replicate inside macrophages will provide additional insight into how it causes disease and may reveal novel targets to be used for drug therapy. Second, since specialized secretion systems are commonly used by a variety of bacterial pathogens, knowledge gained about the L. pneumophila secretion apparatus is likely to be applicable to understanding the molecular mechanisms of virulence used by other pathogens, and could serve as the basis to prevent or treat a number of different diseases.