Mechanisms of the M protein in group A Streptococcus virulence

描述（由申请人提供）：A组链球菌（GAS，S.化脓性链球菌），每年造成约5亿例链球菌性咽喉炎，也能够引起严重的侵袭性疾病（每年10，000例美国病例），具有高死亡率（>30%），如链球菌中毒性休克综合征（STSS）。未经治疗的GAS感染也可能导致严重的自身免疫后遗症，包括急性风湿热。M蛋白是GAS的主要表面相关毒力因子，在这些疾病过程中起着重要作用。M蛋白通过将特异性宿主因子募集到GAS表面来损害GAS的吞噬清除，最常见的是纤维蛋白原（Fg）和C4 b结合蛋白（C4 BP），其干扰调理素抗体的沉积和补体的活化。此外，M1型M蛋白在从GAS表面蛋白水解释放后，与纤维蛋白原形成促炎复合物，从而导致STSS。利用我们最近对M1蛋白及其与Fg相互作用的结构发现，该项目的目标是定义各种M蛋白类型与Fg和C4 BP相互作用的规则。将进行体外和体内实验，以确定M1蛋白如何与Fg形成致病复合物（目标1）;其他M型是否与Fg形成致病复合物，以及如果它们形成致病复合物，这是如何发生的（目标2）;以及非常广泛的M蛋白类型如何通过非保守和缺乏明显序列同源性的区域将C4 BP募集到GAS表面以进行保护（目标3）。一旦完成，这些研究将提供适用于设计新的治疗或预防GAS策略的基本知识。这个多PI提案借鉴了Ghosh和Nizet实验室独特但高度互补的专业知识。Ghosh实验室在细菌毒力因子的生物化学和结构生物学方面拥有丰富的经验，Nizet实验室在A组链球菌（GAS）的分子遗传学以及GAS与宿主先天免疫的体外和体内相互作用研究方面拥有丰富的经验。这个为期五年的项目将扩展联合指导和合作的成功方法，该方法产生了两份描述M1蛋白和M1蛋白-纤维蛋白原复合物的晶体结构的手稿，另一份联合手稿详细介绍了M1蛋白促进GAS抵抗宿主嗜中性粒细胞杀伤的新机制。Ghosh博士将直接指导三名博士后研究人员，专注于生物化学和结构方法，Nizet博士将直接指导一名博士后研究人员，专注于微生物和免疫学方法。

DESCRIPTION (provided by applicant): Group A Streptococcus (GAS, S. pyogenes), which is responsible for ~500 million cases of strep throat annually, is also capable of causing severe invasive diseases (10,000 US cases annually) with high mortality rates (>30%), such as streptococcal toxic shock syndrome (STSS). Untreated GAS infection can also lead to serious autoimmune sequelae, including acute rheumatic fever. The M protein, the major surface-associated virulence factor of GAS, has a significant role in each of these disease processes. The M protein impairs phagocytic clearance of GAS by recruiting specific host factors to the GAS surface, the most common being fibrinogen (Fg) and C4b-binding protein (C4BP), that interfere with the deposition of opsonic antibodies and the activation of complement. Furthermore, the M1 type of M protein, after proteolytic release from the GAS surface, forms a proinflammatory complex with fibrinogen that contributes to STSS. Capitalizing on our recent structural discoveries on the M1 protein and its interactions with Fg, the goals of the project are to define the rules governing the interactions of various M protein types with Fg and with C4BP. In vitro and in vivo experiments will be carried out to determine how the M1 protein forms a pathogenic complex with Fg (Aim 1); whether other M types form pathogenic complexes with Fg, and if they do so, how this occurs (Aim 2); and how a remarkably broad variety of M protein types recruit C4BP to the GAS surface for protection through a region that is non-conserved and lacks apparent sequence homology (Aim 3). Once completed, these studies will provide essential knowledge applicable to the design of novel therapeutics or preventive strategies against GAS. This multi-PI proposal draws on the distinct yet highly complementary sorts of expertise in the Ghosh and Nizet laboratories. The Ghosh laboratory has extensive experience with the biochemistry and structural biology of bacterial virulence factors, and the Nizet laboratory has extensive experience in the molecular genetics of group A Streptococcus (GAS) and the study of GAS interactions with host innate immunity in vitro and in vivo. This five-year project will extend a successful approach of joint mentorship and collaboration that has yielded two manuscripts describing the crystal structures of M1 protein and the M1 protein-fibrinogen complex, and another joint manuscript detailing novel mechanisms by which M1 protein promotes GAS resistance to host neutrophil killing. Dr. Ghosh will directly supervise three postdoctoral researchers focusing on biochemical and structural approaches, and Dr. Nizet will directly supervise one postdoctoral researcher focusing on microbiological and immunological approaches.