The molecular mechanism of Legionella type IV secretion

描述（由申请人提供）：嗜肺军团菌是一种革兰氏阴性菌，可在环境中的淡水变形虫体内复制，但也可通过在肺泡巨噬细胞内复制而引起人类军团病。嗜肺乳杆菌在正常的杀菌吞噬细胞内存活并复制，通过改变其内吞途径，从而抑制吞噬体-溶酶体快速融合。嗜肺乳杆菌通过IV型分泌系统（T4SS）向宿主注入大量毒力因子，从而扰乱宿主正常细胞功能。嗜肺乳杆菌T4SS由26个dot或icm基因编码，这些基因编码细菌细胞包膜中的大型大分子复合物。由于该系统的复杂性，嗜肺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技术，TrIP（易位免疫沉淀），可以详细了解t4ss的底物分泌。使用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分泌系统的功能。这项研究将在两个方面与人类健康有关。首先，建立嗜肺乳杆菌在巨噬细胞内存活和复制的机制将为其如何引起疾病提供额外的见解，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，因此对嗜肺乳杆菌分泌装置的了解可能适用于理解其他病原体使用的毒力的分子机制，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.