Abstract：
Shigella spp. are highly pathogenic members of the Enterobacteriaceae family, causing ∼269 million cases of bacillary dysentery and >200,000 deaths each year. Like many Gram-negative pathogens, Shigella rely on their type three secretion system (T3SS) to inject effector proteins into eukaryotic host cells, driving both cellular invasion and evasion of host immune responses. Exposure to the bile salt deoxycholate (DOC) significantly enhances Shigella virulence and is proposed to serve as a critical environmental signal present in the small intestine that prepares Shigella\'s T3SS for efficient infection of the colonic epithelium. Here, we uncover critical mechanistic details of the Shigella-specific DOC signaling process by describing the role of a π-helix secondary structure element within the T3SS tip protein invasion plasmid antigen D (IpaD). Biophysical characterization and high-resolution structures of IpaD mutants lacking the π-helix show that it is not required for global protein structure, but that it defines the native DOC binding site and prevents off target interactions. Additionally, Shigella strains expressing the π-helix deletion mutants illustrate the pathogenic importance of its role in guiding DOC interaction as flow cytometry and gentamycin protection assays show that the IpaD π-helix is essential for DOC-mediated apparatus maturation and enhanced invasion of eukaryotic cells. Together, these findings add to our understanding of the complex Shigella pathogenesis pathway and its evolution to respond to environmental bile salts by identifying the π-helix in IpaD as a critical structural element required for translating DOC exposure to virulence enhancement.
摘要：
志贺氏菌属。是肠杆菌科的高致病性成员，每年造成2.69亿例细菌性痢疾和>20万人死亡。像许多革兰氏阴性病原体一样，志贺氏菌依靠其三型分泌系统（T3SS）将效应蛋白注入真核宿主细胞，驱动细胞入侵和逃避宿主免疫反应。暴露于胆汁盐脱氧胆酸盐（DOC）可显着增强志贺氏菌的毒力，并被建议作为小肠中存在的关键环境信号，为志贺氏菌的T3SS有效感染结肠上皮。这里,我们通过描述T3SS尖端蛋白IpaD中π-螺旋二级结构元件的作用,揭示了志贺氏菌特异性DOC信号传导过程的关键机制细节.缺乏π螺旋的IpaD突变体的生物物理表征和高分辨率结构表明，它不是全局蛋白质结构所必需的。但它定义了原生DOC结合位点并防止脱靶相互作用。此外,表达π-螺旋缺失突变体的志贺氏菌菌株说明了其在指导DOC相互作用中的作用的致病性重要性，因为流式细胞术和庆大霉素保护试验表明，IpaDπ-螺旋对于DOC介导的装置成熟和增强的真核细胞侵袭至关重要。一起,通过将IpaD中的π-螺旋识别为将DOC暴露转化为毒力增强所需的关键结构元素,这些发现增加了我们对复杂志贺氏菌发病途径及其对环境胆汁盐的反应的进化的理解.
