病原微生物蛋白质调控线性泛素组装复合物LUBAC的机制研究和小分子调节剂的发现

线性泛素化是一种广泛参与免疫和NF-kB通路的翻译后修饰。线性泛素链组装复合物（LUBAC）是合成线性泛素链的唯一E3连接酶。多种微生物能靶向调节它；例如，导致痢疾的志贺菌分泌E3连接酶IpaH1.4/2.5，介导LUBAC的降解；人类T淋巴细胞白血病I型病毒（HTLV-1）的Tax劫持LUBAC，促进细胞的转化； HBV病毒的HBx与LUBAC结合后促进病毒基因表达。此外，淋巴细胞的抗原受体复合物切割LUBAC的亚基HOIL-1L，生成的片段能负反馈抑制NF-kB通路。. 病原微生物蛋白质识别LUBAC的机制仍未知。我们运用结构生物学和生物化学，解析相关蛋白质与LUBAC的复合物结构，阐述它们的作用机制和对NF-kB通路的调控，并筛选相关的小分子化合物。我们解析HOIL-1L的结构，揭示催化机理和负反馈抑制NF-kB的机制。此研究有助我们理解病原微生物如何调节免疫和治疗相关疾病。

Linear ubiquitination is a type of reversible post-translational modification that broadly participates in the immune pathways. The linear ubiquitin chain assembly complex (LUBAC) is the sole E3 ligase that can form linear ubiquitin chain, and is an important target of effector proteins from many pathogens. For example, the IpaH1.4/2.5 protein secreted by Shigella flexneri ubiquitinates LUBAC and targets it to degradation through ubiquitin-proteasome pathway; The Tax protein from HTLV-1 (human T cell lymphoma virus I) also hijacks LUBAC, causes persistent activation of NF-kB pathway and promotes the transformation of infected cell and development of cancer; The X protein (HBx) from human hepatitis B virus (HBV) activates the expression of HBV genome after its binding to LUBAC. In addition, the antigen receptor complex in stimulated T or B cells recruits LUBAC to activate NF-kB pathway firstly, then the protease MALT1 in the complex cuts the HOIL-1L protein into two fragments, one of the E3-activity containing fragment (NZF-RBR) gains the ability to suppress NF-kB, and constitutes a negative feedback loop, which is important for the proper response and shutdown of NF-kB pathway...Although the biological significance of LUBAC in the innate immune pathway is well proved, the molecular mechanisms for the interaction between LUBAC and pathogenic effector proteins are still poorly understood; especially, how the effector proteins (IpaH1.4/2.5, Tax, HBx) recognize LUBAC, and how the NZF-RBR of HOIL-1L fragment inhibits NF-kB pathway? We propose to answer these questions through structural and biochemical studies. We will determine the structures of the complexes formed between IpaH1.4/Tax/HBx and HOIL-1L/HOIP, and screen for the inhibitory compounds that can modulate these interactions. Meanwhile, we will find out the catalytic mechanism of HOIL-1L and how HOIL-1L forms a negative feedback to inhibit NF-kB pathway. The findings from this project will deepen our understanding of interaction between pathogen and innate immune, and provide new perspective and tool to intervene relative diseases.