Typhoid Toxin and Salmonella Typhi pathogenesis

项目描述 伤寒沙门氏菌（S.伤寒）和相关血清型S.副伤寒引起伤寒， 这是一种毁灭性的疾病，每年导致约20万人死亡。虽然大多数情况下， 在发展中国家，美国偶尔也会爆发疫情。与其他沙门氏菌不同 血清型可感染多种宿主并可引起有限的胃肠炎，S。伤寒是一个独家 人类病原体，并导致全身性，往往是致命的疾病。尽管公共卫生的重要性， 伤寒沙门氏菌的发病机制仍然知之甚少。我们的实验室已经 探索S.伤寒的发病机制，并投入了大量的精力，研究 伤寒毒素，一种在伤寒沙门氏菌血清型中高度保守的A2B5毒素（即，e. S.伤寒和沙门氏菌。 副伤寒），但它在非伤寒沙门氏菌中基本上不存在。伤寒毒素是一种非典型的AB毒素， 与所有已知的AB 5毒素家族成员不同，它有两个酶活性亚基：ADP核糖基 转移酶（PltA）与尚未鉴定的宿主靶标，以及脱氧核糖核酸酶（CdtB），其使DNA 对中毒细胞的损害。这两个亚基彼此共价连接，并结合到一个 由Plt B组成同型五聚体B亚基。伤寒毒素是唯一适应人类，因为它认识到， 表面糖蛋白上的Neu5Ac终止的唾液酸聚糖。伤寒毒素对实验性 动物可以复制伤寒的许多急性特征性症状，包括木僵， 嗜睡，最有可能涉及中枢神经系统（CNS）。伤寒毒素具有显著的 生物学，因为它只由细胞内的细菌产生，在合成和组装后，它被释放出来， 进入含沙门氏菌的液泡，随后通过特异性的 囊泡运输载体。在过去的资助期间，我们已经解开了许多机械方面的， 伤寒毒素的生物学，包括其独特的细胞内表达机制的描述， 其显着的运输途径的所有步骤的表征，新的细菌蛋白质的发现 分泌机制，其独特的进化历史的描述，并发现一种替代 伤寒毒素的一种。最后，这些研究导致了一种新的细胞内在病原体的发现 限制机制，防止复制的S。伤寒在小鼠组织中的作用， 小鼠病原体S.鼠伤寒杆菌通过特定III型蛋白分泌效应物的活性缺失 来自酿脓链球菌伤寒这些研究提出了与伤寒发病机制相关的非常重要的问题， 我们打算在下一个资助期内继续推行。

PROJECT DESCRIPTION Salmonella enterica serovar Typhi (S. Typhi) and the related serovar S. Paratyphi cause typhoid fever in humans, a devastating disease that results in ~200,000 deaths every year. Although most of the cases occur in developing countries, outbreaks occasionally occur in the United States. Unlike other Salmonella enterica serovars, which can infect a variety of hosts and can cause limited gastroenteritis, S. Typhi is an exclusive human pathogen and causes systemic, often lethal, disease. Despite its Public Health importance, the mechanisms of pathogenesis of typhoidal Salmonellae remain poorly understood. Our laboratory has been exploring the unique aspects of S. Typhi pathogenesis and devoted a substantial amount of effort to the study of typhoid toxin, an A2B5 toxin that is highly conserved in typhoidal Salmonella serovars (i. e. S. Typhi and S. Paratyphi), but that it is largely absent from non-typhoidal Salmonellae. Typhoid toxin is an atypical AB toxin in that, unlike all known AB5 toxin family members, it has two enzymatically active subunits: an ADP ribosyl transferase (PltA) with an as of yet unidentified host target, and a deoxyribonuclease (CdtB), which inflicts DNA damage on intoxicated cells. These two subunits are covalently linked to one another and are associated to a homopentameric B subunit composed of PltB. Typhoid toxin is uniquely adapted to humans as it recognizes Neu5Ac-terminated sialoglycans on surface glycoproteins. Administration of typhoid toxin to experimental animals can reproduce many of the acute pathognomonic symptoms of typhoid fever, including stupor and lethargy, which most likely involve the central nervous system (CNS). Typhoid toxin exhibits a remarkable biology in that it is only produced by intracellular bacteria, and after its synthesis and assembly, it is released into the Salmonella-containing vacuole and subsequently transported to the extracellular space by specific vesicle transport carriers. During the past funding period we have unraveled many mechanistic aspects of the biology of typhoid toxin, including the description of its unique mechanism of intracellular expression, the characterization of all the steps of its remarkable transport pathways, the discovery of novel bacterial protein secretion mechanism, the description of its unique evolutionary history, and the discovery of an alternative form of typhoid toxin. Finally, these studies have led to the discovery of a novel cell-intrinsic pathogen restriction mechanism that prevents the replication of S. Typhi in mouse tissues and that it is antagonized by the mouse pathogen S. Typhimurium through the activity of specific type III protein secretion effectors absent from S. Typhi. These studies have raised very important questions related to pathogenesis of typhoid fever that we intend to pursue during the next funding period.