Structure-function analysis of type IVB secretion systems

摘要 嗜肺军团菌是一种革兰氏阴性细菌，在环境中的原生动物体内复制， 也可以在肺泡巨噬细胞内复制，从而引起一种类似肺炎的疾病， 军团病。L.嗜肺菌能够在正常的杀菌环境中存活和复制， 通过改变吞噬细胞的内吞途径和阻止吞噬体-溶酶体的快速融合，L. 嗜肺菌通过向宿主体内注入大量毒力因子来扰乱宿主细胞的正常功能 通过IVB型分泌系统（T4 BSS）在细胞质中表达。洛杉矶嗜肺菌T4 BSS由20个- 7个dot/icm基因，编码细菌细胞包膜中的大分子复合物。的 Dot/Icm系统是细胞生长和毒力的必需系统。相比之下，大多数 由于多个冗余水平，约300 Dot/Icm底物似乎对两个性状都是不稳定的。 因此，L. Dot/Icm代表了治疗干预的最可行的靶标。 尽管已经获得了关于本发明的组件和功能的大量信息， Dot/Icm系统，许多问题仍然存在。这项建议将对最近在以下方面取得的一些进展采取后续行动： Dot/Icm T4BSS其中包括发现Dot/Icm系统位于地球的两极， 细菌和极性出口的基板，这一专门的分泌系统是必要的， LCV（含空泡军团菌）的细胞内靶向。第二个重大进步是 确定与分泌分子伴侣结合的DotL的C-末端的结构。最终 最新进展是通过cryoEM获得了该分泌器官的第一张图像。总的来说，这项研究 与人类健康的关系。第一，建立了L.嗜肺菌 在巨噬细胞内存活和复制将为它如何引起疾病提供更多的见解， 揭示了用于药物治疗的新靶点。其次，由于专门的分泌系统是 通常被各种细菌病原体使用，关于L.嗜肺分泌 仪器可能适用于理解其他病毒所使用的毒力的分子机制， 病原体，并可以作为预防或治疗许多不同疾病的基础。

Abstract Legionella pneumophila is a Gram-negative bacteria that replicates inside protozoa in the environment but can also replicate within alveoloar macrophages, thereby causing a pneumonia-like disease called Legionnaires’ disease. L. pneumophila is able to survive and replicate within normally bactericidal phagocytic cells by altering their endocytic pathway and preventing rapid phagosome-lysosome fusion. L. pneumophila perturbs normal host cell function by injecting a large number of virulence factors into the host cell cytoplasm via a type IVB secretion system (T4BSS). The L. pneumophila T4BSS is encoded by twenty- seven dot/icm genes, which encode a large macromolecular complex in the bacterial cell envelope. The Dot/Icm system is absolutely required for intracellular growth and virulence. In contrast, the majority of the ~300 Dot/Icm substrates appear to be dispensable for both traits due to multiple levels of redundancy. Therefore, the L. pneumophila Dot/Icm represents the most viable target for therapeutic intervention. Although a significant amount of information has been acquired about the assembly and function of the Dot/Icm system, many questions remain. This proposal will follow-up on a number of recent advances on the Dot/Icm T4BSS. These include the discovery that the Dot/Icm system is located at the poles of the bacterium and polar export of substrates by this specialized secretion system is required for proper intracellular targeting of the LCV (Legionella containing vacuole). The second major advance was the determination of the structure of the c-terminus of DotL bound to the secretion chaperones. The final advance was the acquisition of the first image of this secretion apparatus by cryoEM. Overall this research relates to human health in several 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.