Exploring the Strategies of Bacterial Subversion of the Host Ubiquitin System: The Mechanism of Novel E3 Ligases (NEL) from Shigella

本项目的目的是阐明细菌泛素连接酶破坏受感染细胞的先天免疫反应的机制。我们的理解将有助于发现新的治疗策略，以应对新出现的抗生素耐药性威胁。先天免疫反应是抵抗细菌感染的第一道防线。它涉及各种细胞反应的激活，导致感染组织的炎症。炎症反应的激活步骤在很大程度上取决于细胞的泛素化机制。泛素化机制由一系列不同的酶组成，这些酶依次作用，用泛素链修饰靶蛋白。泛素链由小蛋白泛素组成。泛素链的连接受到一类称为E3泛素连接酶的酶的严格调节和催化。许多病原菌部署一组E3泛素连接酶，它们将其引入受感染宿主细胞的胞质溶胶中。这些细菌泛素连接酶，称为NEL（新型E3连接酶），能够用泛素修饰宿主泛素化机制的组分。细菌NEL的活性干扰宿主泛素化机制的正常功能，这最终破坏了有利于入侵病原体的先天免疫应答。目前尚不清楚NEL如何劫持宿主泛素化机制来修饰其靶蛋白。人类病原体福氏志贺菌是高度传染性的细菌，是导致称为志贺菌病的严重形式的痢疾的原因。志贺氏菌病是世界范围内发病和死亡的重要原因.志贺氏菌的一些NEL靶向线性泛素链组装复合物LUBAC，这导致复合物的功能干扰。LUBAC是泛素化机制的关键组分，并且是细菌感染后激活炎症反应所必需的。我们将使用结构和生物物理技术相结合，以确定分子机制，其中来自志贺氏菌的NEL IpaH 1.4修饰LUBAC与泛素，并揭示这种修饰如何抑制LUBAC活性。我们的研究结果将有助于阐明志贺菌致病的分子机制，并可能为限制细菌感染提供新的途径。

The aim of this project is to elucidate the mechanism by which bacterial ubiquitin ligases undermine the innate immune response of an infected cell. Our understanding will help to uncover new therapeutic strategies to fight the emerging threat of antimicrobial resistance. The innate immune response is the first line of defence against bacterial infections. It involves activation of a variety of cellular reactions, which cause inflammation of the infected tissue. The activation steps of the inflammatory response depend to a great extent on the ubiquitylation machinery of the cell. The ubiquitylation machinery consists of a cascade of different enzymes, which act in sequence to modify target proteins with ubiquitin chains. Ubiquitin chains consist of the small protein ubiquitin. The attachment of ubiquitin chains is tightly regulated and catalysed by a class of enzymes known as E3 ubiquitin ligases. Many pathogenic bacteria deploy a set of E3 ubiquitin ligases which they introduce into the cytosol of the infected host cell. These bacterial ubiquitin ligases, known as NELs (Novel E3 Ligase), are capable to modify components of the host ubiquitylation machinery with ubiquitin. The activity of the bacterial NELs interferes with normal function of the host ubiquitylation machinery which ultimately subverts the innate immune response in favour of the invading pathogen. It is currently unknown how NELs highjack the host ubiquitylation machinery to modify their target proteins. The human pathogen Shigella flexneri are highly infectious bacteria which are responsible for a severe form of dysentery known as shigellosis. Shigellosis a significant cause of morbidity and mortality worldwide. Some NELs from Shigella are targeting the linear ubiquitin chain assembly complex LUBAC which results in functional interference of the complex. LUBAC is a key component of the ubiquitylation machinery and required for the activation of the inflammatory response upon bacterial infection. We will use a combination of structural and biophysical techniques to determine the molecular mechanism by which the NEL IpaH1.4 from Shigella modifies LUBAC with ubiquitin and uncover how this modification inhibits LUBAC activity. Our findings will shed light on the molecular mechanism of Shigella pathogenesis and may provide new routes to restrict bacterial infections.