A periplasmic global regulator, ExoR, for bacterial invasion of host cells

描述（由申请人提供）：植入医疗器械的细菌感染和表面定植是并将继续是主要的健康威胁，尤其是随着多种耐药病原体的发展。细菌病原体依靠其膜传感器来检测宿主细胞的存在，以便在正确的时间产生毒力因子来入侵宿主细胞或在医疗器械表面定殖。阻断细菌对宿主的感知可能是阻止细菌感染的一种新方法。作为我们长期努力了解宿主细胞入侵过程中细菌传感和信号传导的一部分，我们正在研究苜蓿中华根瘤菌ExoR蛋白在控制从自由活细胞到入侵准备细胞的转换中的分子机制。我们以前已经表明，ExoR蛋白和ExoS/ChvI双组分调节系统反向调节宿主细胞入侵所需的多糖（琥珀多糖）和细菌运动所需的鞭毛的产生。我们目前的假设是ExoR蛋白的活性形式（ExoRm）结合ExoS并使其保持在OFF状态，从而改变由ExoS/ChvI系统调节的基因的表达。周质中ExoRm的量通过反馈调节和ExoRm的蛋白水解以产生ExoRc 20来维持。ExoRm蛋白水解速率的变化被细胞用来感知环境刺激，控制自由生活和附着生活之间的转换。这个模型是基于过去两年中的以下关键发现。首先，ExoR在ExoS/ChvI双组分调控系统的上游发挥作用，负调节ExoS的活性;其次，ExoR通过反馈调节进行自调节;第三，ExoR在周质中被消化产生ExoRc 20。我们计划1）通过分别表达不同形式的ExoR、ExoRp、ExoRm和ExoRc 20来确定不同形式的ExoR蛋白的功能;并通过检查它们的生物学功能和它们与ExoS蛋白直接相互作用的能力; 2）通过表征ExoR蛋白水解的分子机制来确定ExoR蛋白水解的分子机制及其调节;鉴定调节ExoR蛋白水解的环境刺激，并鉴定S.苜蓿ExoR蛋白酶。我们的新发现可以立即应用于了解与S有密切同源物的56种动植物病原体的致病性。苜蓿我们的新发现将有助于开发控制细菌感染的新方法。 公共卫生相关性：在感知到宿主的存在后，大多数病原菌会产生特殊的产物来增强它们感染宿主细胞的能力。我们的研究将导致开发新的方法来控制细菌感染，通过阻断它们感知宿主存在的能力。

DESCRIPTION (provided by applicant): Bacterial infections and surface colonization of implanted medical devices are and will continue to be major health threats especially with the development of multiple drug resistant pathogens. Bacterial pathogens rely on their membrane sensors to detect the presence of host cells in order to produce virulence factors at the right time to invade host cells or colonize the surface of medical devices. Blocking bacterial sensing of hosts could be a new approach to stop bacterial infection. As part of our long term effort to understand bacterial sensing and signaling during host cell invasion, we are studying the molecular mechanism of Sinorhizobium meliloti ExoR protein in controlling the switch from free living cells to invasion ready cells. We have shown previously that both the ExoR protein and the ExoS/ChvI two-component regulatory system regulates inversely the production of a polysaccharide (succinoglycan) required for host cell invasion, and flagella, required for bacterial motility. Our current hypothesis is that the active form of the ExoR protein (ExoRm) binds ExoS and keeps it in the OFF state, altering the expression of the genes regulated by ExoS/ChvI system. The amount of ExoRm in the periplasm is maintained through feedback regulation and the proteolysis of ExoRm to produce ExoRc20. The changes in ExoRm proteolysis rate is being used by the cells to sense environmental stimuli control the switch between free living and attached living. This model is based on the following key discoveries made in the last two years. First, ExoR functions upstream of ExoS/ChvI two-component regulatory system and negatively regulates the activity of ExoS; Second, ExoR autoregulates through feedback regulation; Third, ExoR is digested in periplasm to generate ExoRc20. We plan to 1) determine the function of different forms of ExoR proteins by expressing different forms of ExoR, ExoRp, ExoRm, and ExoRc20, individually; and by examining their biological functions and their ability to interact directly with ExoS protein; 2) determine the molecular mechanisms of ExoR proteolysis and its regulation by characterizing the molecular mechanism of ExoR proteolysis; identifying environmental stimuli modulating ExoR proteolysis, and identifying the S. meliloti ExoR protease. Our new discoveries can be applied immediately to the understanding of the pathogenicities of 56 animal and plant pathogens that have close homologs of S. meliloti ExoR. Our new discoveries will contribute to the development of new approaches to control bacterial infections. PUBLIC HEALTH RELEVANCE: After sensing the presence of their hosts, most pathogenic bacteria produce special products to enhance their abilities to infect host cells. Our study will lead to the development of new approaches to control bacterial infections by blocking their abilities to sense of the presence of their hosts.