Typhoid Toxin and Salmonella Typhi pathogenesis

项目说明 伤寒沙门氏菌及相关副伤寒沙门氏菌可引起 人类，这是一种毁灭性的疾病，每年导致约20万人死亡。尽管大多数案件都发生在 在发展中国家，疫情偶尔会在美国发生。与其他肠道沙门氏菌不同 伤寒沙门氏菌是一种可以感染多种宿主并引起局限性胃肠炎的血清型 人类病原体，并引起全身性疾病，通常是致命的。尽管它对公共卫生很重要，但 伤寒沙门氏菌的致病机制尚不清楚。我们的实验室已经 探索伤寒沙门氏菌致病机制的独特方面，并投入了大量精力进行研究 伤寒毒素是一种A2B5毒素，在伤寒沙门氏菌血清(即伤寒沙门氏菌和沙门氏菌)中高度保守。 副伤寒)，但在非伤寒沙门氏菌中基本不存在。伤寒毒素是一种非典型的AB毒素。 与所有已知的AB5毒素家族成员不同，它有两个具有酶活性的亚基：ADP核糖基 转移酶(PltA)和脱氧核糖核酸酶(CDtB)，前者具有未知的宿主靶标，后者可导致DNA 对醉酒细胞的损害。这两个亚基相互共价连接，并与 由PltB组成的同源五聚体B亚基。伤寒毒素独特地适应于人类，因为它识别 表面糖蛋白上的Neu5Ac-末端唾液酸聚糖。伤寒毒素对实验动物的影响 动物可以复制伤寒的许多急性病原体症状，包括昏迷和 嗜睡，这很可能涉及中枢神经系统(CNS)。伤寒毒素表现出显著的 生物学：它只由细胞内的细菌产生，合成和组装后被释放 进入含有沙门氏菌的液泡，然后通过特定的方式运输到细胞外空间 囊泡运输载体。在过去的资助期内，我们揭开了 伤寒毒素的生物学，包括其独特的细胞内表达机制的描述，伤寒毒素的 表征其非凡的运输途径的所有步骤，发现新的细菌蛋白 分泌机制，描述其独特的进化史，并发现替代 伤寒毒素的形式。最后，这些研究导致了一种新的细胞内源性病原体的发现 阻止伤寒沙门氏菌在小鼠组织中复制的限制机制，并被 鼠伤寒沙门氏菌通过特异性III型蛋白分泌效应器的活性缺失 来自伤寒沙门氏菌。这些研究提出了与伤寒发病机制有关的非常重要的问题 我们打算在下一个资金期内继续努力。

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.