金黄色葡萄球菌群体感应信号分子AI-2的受体鉴定及调控致病性的分子机制

Quorum sensing is a bacterial cell-cell communication mechanism in which individuals coordinate their population behavior in a density-dependent manner. It has been widely recognized that AHLs and oligopeptides can act as quorum sensing signals, and autoinducer 2 (AI-2)-mediated quorum sensing has been functionally and mechanically revealed. Our previous data indicated that AI-2 can regulate virulence by serving as a signaling molecule in Staphylococcus aureus, but the AI-2 receptor and regulatory mechanism remain mysterious. Genetic deletion of luxS encoding AI-2 synthase led to a higher transcription level of saaR encoding a transcriptional factor. The phenotypes of virulence were coordinated when luxS or saaR was deleted respectively. Cryoelectron microscopy analysis suggests that SaaR can specifically bind to AI-2. These results imply that binding between AI-2 and SaaR can change the conformation of the transcriptional factor, by which AI-2/SaaR perform quorum sensing regulation and coordinate population behavior. This study aims to elucidate the molecular mechanisms of virulence modulated by AI-2/SaaR quorum sensing. This research will not only deepen our understanding of the function and regulatory mechanisms of quorum sensing in Staphylococcus aureus, but also provide novel targets and strategies for the treatment of infection caused by Gram-positive bacterial pathogens.

群体感应是细菌通过个体间通讯实现密度依赖性种群行为的调控机制。酰基高丝氨酸内酯及寡肽作为信号分子介导的群体感应被广泛研究，且AI-2群体感应在革兰氏阴性细菌中的功能也较为清楚。我们发现金黄色葡萄球菌AI-2信号分子能够调控致病性，但是通过何种受体及具体的调控机制尚不清楚。敲除AI-2合成酶基因luxS可导致转录因子SaaR编码基因表达水平提高，而分别敲除luxS与saaR后，致病性基因的表达变化呈现相关性。冷冻电镜实验初步证明，SaaR可以与AI-2分子产生特异性结合效应。这些结果显示AI-2信号分子可能通过结合SaaR使其发生构象变化，来行使AI-2/SaaR的群体感应调控功能，由此调控相关靶基因的转录水平和群体行为。本项目期望揭示金黄色葡萄球菌AI-2/SaaR群体感应调控致病性的分子机制 ，为革兰氏阳性细菌病原体感染治疗提供新型药物靶点和策略。

群体感应是细菌通过个体间通讯实现密度依赖性种群行为的调控机制。LuxS/AI-2群体感应系统广泛存在于革兰阳性和阴性细菌，可以通过调控毒力因子影响细菌的感染能力和侵袭能力，进而影响致病性。我们的工作表明，金黄色葡萄球菌AI-2能够行使群体感应信号分子的功能，并且可以影响其致病性。体内外实验表明我们发现了AI-2受体蛋白质SaaR（Rbf）。冷冻电镜三维结构分析表明，Rbf与AI-2分子可以产生特异性结合效应。qRT-PCR与EMSA实验结果表明，LuxS/AI-2系统以AI-2剂量依赖的方式抑制Rbf的表达，且Rbf能够特异性结合到自己的启动子并且正调控rbf的表达。.Rbf不仅自身具有重要的调控功能，并且处于金葡菌毒力与生物被膜调控网络的关键枢纽。DNA pull-down结果显示，Rbf处于MgrA-ArlR级联调控的下游，MgrA与ArlR作为金葡菌重要的全局性调控因子，均可通过特异性结合启动子的方式抑制rbf的表达，从而引发下游毒力与生物被膜的多种生理变化。这表明Rbf在金葡菌的信号调控网络中起到关键的连结作用。.Rbf作为首个在革兰氏阳性细菌中被发现的AI-2受体，可能成为解读金葡菌AI-2群体感应系统调控功能的关键节点。进一步研究金葡菌AI-2/ Rbf群体感应及调控机制，不仅有助于深入理解AI-2群体感应在细菌种间通讯中的重要性，也可能为金葡菌及其它革兰阳性细菌病原体的感染治疗提供新的靶标与策略。