志贺氏菌的致病性源自积聚于侵袭性大质粒中约31Kb的”entry region”的毒力基因，这些毒力基因编码了三型分泌系统（T3SS）的调控蛋白，结构蛋白，伴侣蛋白和效应因子等大量蛋白质。毒力基因的表达受到严格调控，环境不适宜时，毒力基因的转录受H-NS蛋白抑制；适宜环境时，诱导VirB蛋白表达，最终激活毒力基因表达。我们前期研究初步阐明了VirB蛋白核心结构域结合启动子上游顺式序列，从而解除H-NS抑制毒力基因表达的分子机制。然而VirB蛋白结构信息的不完整性，严重制约这一重要转录调控蛋白的工作原理。本课题拟在前期研究基础上，通过解析VirB-DNA复合物晶体结构，溶液结构和电镜结构，深入阐明VirB间接识别DNA的分子机制，详细提出VirB解除H-NS介导的转录抑制作用的分子模型。预期结果将为阐明志贺氏菌致病机理提供结构生物学证据，为相关的抑制剂及药物设计提供科学理论依据。

The virulence genes clustering at “entry region” of the virulence plasmid determine the virulence of Shigella, and they encode the type III secretion system and the invasion and the effector proteins required for the invasion of intestine cells. Expression of these virulence genes is tightly regulated. When circumstance is not favorable for invasion, transcription of the virulence genes are repressed by the chromosome encoded H-NS protein; once environment is favorable, expression of VirB gene is induced and invasion occurs. Our previous studies have shown that core structural domain of VirB protein can relief the H-NS mediated transcriptional repression and activate the expression of the virulence genes by binding the cis-acting element upstream of the promoter and remodeling DNA structure. However, lack of complete structure information of VirB-DNA complex prevents our further understanding of the mechanism of how VirB protein precisely regulates this process. In this study, we propose to resolve the VirB-DNA structure and combine it with SAXS and Cryo-EM methods to further elucidate how VirB protein regulates H-NS mediated suppression. Our project will provide the important structural basis for the understanding of Shigella pathogenesis and inhibitor design.