Role of the Coxiella burnetii Cryptic Plasmid in Host Cell Parasitism

描述（由申请方提供）：贝氏柯克斯体是一种细胞内细菌病原体，是人类Q热（一种急性衰弱性流感样疾病，可进展为慢性心内膜炎）的病原体。自70多年前发现以来，病原体寄生宿主细胞的机制仍然知之甚少。在感染过程中，C.贝氏菌主动调节多种宿主过程，包括囊泡运输和细胞存活。介导这些事件的细菌蛋白质是未知的，但可能通过Dot/Icm IV型分泌系统递送到宿主细胞溶质。当前的应用程序被设计为功能上表征C。Burnetii质粒编码的Dot/Icm底物，并确定其在毒力中的作用。全是C。贝氏体分离物或者具有大的隐蔽质粒，或者具有整合到它们的染色体中的质粒序列，这表明这些分子对于病原体生物学是关键的。有趣的是，我们已经鉴定了由C编码的六个Dot/Icm底物。贝氏体质粒基因称为柯克斯体质粒效应子A-F（CpeA-F）。这些蛋白质中的三个在所有分离株中是保守的，并且三个对来自人类急性疾病分离株的QpH 1质粒是特异性的。目的1是研究保守的CpeB和CpeD分别与自噬体和分泌细胞器的相互作用。目标2将定义感染期间所有六种质粒效应子的需求。此外，这一目标将确定效应子结合宿主蛋白，并确定这些组件的C。贝氏体感染目标3将决定C. Burnetii质粒在细胞培养和Q热豚鼠感染模型中的病原体毒力。总的来说，当前应用程序中的目标将提供对C. Burnetii有效地寄生宿主细胞。这些研究也将提供关于C.贝氏隐质粒在病原菌毒力中的作用。 公共卫生相关性：贝氏柯克斯体是一种细胞内细菌病原体，可引起人畜共患Q热，这是一种使人衰弱的急性疾病，也表现为慢性心内膜炎。目前，C.贝氏体毒力决定因子知之甚少。对C.通过Dot/Icm IV型分泌系统递送到宿主胞质溶胶的贝氏体蛋白将提供对抗Q热的候选治疗靶标，并将提供对C. Burnetii及其宿主。本研究的主要目的是：1）研究C.贝氏体质粒编码的Dot/Icm底物与宿主蛋白质的关系和2）确定质粒在病原体毒力中的作用。

DESCRIPTION (provided by applicant): Coxiella burnetii is an intracellular bacterial pathogen and the etiologic agent of human Q fever, an acute debilitating flu-like illness that can progress to chronic endocarditis. Since its discovery over 70 years ago, mechanisms used by the pathogen to parasitize host cells remain poorly understood. During infection, C. burnetii actively regulates multiple host processes, including vesicular trafficking and cell survival. The bacterial proteins mediating these events are not known but are likely delivered to the host cytosol by a Dot/Icm type IV secretion system. The current application is designed to functionally characterize C. burnetii plasmid-encoded Dot/Icm substrates and define their role in virulence. All C. burnetii isolates either harbor a large cryptic plasmid or have plasmid sequences integrated into their chromosome, suggesting these molecules are critical for pathogen biology. Interestingly, we have identified six Dot/Icm substrates encoded by C. burnetii plasmid genes that are termed Coxiella plasmid effectors A - F (CpeA - F). Three of these proteins are conserved in all isolates and three are specific to the QpH1 plasmid from a human acute disease isolate. Aim 1 is designed to characterize the interaction of conserved CpeB and CpeD with autophagosomes and secretory organelles, respectively. Aim 2 will define requirements of all six plasmid effectors during infection. Additionally, this aim will identify effector binding host proteins and determine the requirement of these components for C. burnetii infection. Aim 3 will determine the requirement of the C. burnetii plasmid for pathogen virulence in both cell culture and a guinea pig infection model of Q fever. Collectively, the aims in the current application will provide needed insight into the mechanisms used by C. burnetii to efficiently parasitize host cells. These studies will also provide novel information regarding the role of the C. burnetii cryptic plasmid in pathogen virulence. PUBLIC HEALTH RELEVANCE: Coxiella burnetii is an intracellular bacterial pathogen that causes the zoonosis human Q fever, a debilitating acute disease that also presents as chronic endocarditis. Currently, C. burnetii virulence determinants are poorly understood. Characterization of C. burnetii proteins delivered to the host cytosol by the Dot/Icm type IV secretion system will provide candidate therapeutic targets to combat Q fever and will provide needed insight into the interactions between C. burnetii and its host. The goals of the proposed research are to 1) characterize the interaction of C. burnetii plasmid-encoded Dot/Icm substrates with host proteins and 2) determine the role of the plasmid in pathogen virulence.)