细菌外源基因抑制因子的结构与功能研究

基因水平转移对细菌的进化影响重大，很多毒力基因及抗生素抗性基因都是以这种方式被细菌获取。同时，这些基因的不恰当表达会降低细菌的生存能力。因此，许多细菌进化出外源基因抑制因子，选择性地结合并抑制外源基因的转录。外源基因抑制因子是许多毒力和耐药性基因的重要调控因子，在结核分枝杆菌、霍乱弧菌、致病性大肠杆菌和绿脓杆菌等病原菌中发挥重要作用。在细菌中已发现四类外源基因抑制因子：变形杆菌中的H-NS，分支杆菌中的Lsr2，假单胞菌中的MvaT，以及芽孢杆菌中的Rok。我们已阐明Lsr2和H-NS都运用了类似AT-hook的机理结合DNA，相关结果分别于2010和2011年发表在PNAS上。MvaT和Rok都不具有AT-hook类似结构，它们自聚合性质也缺少研究。本项研究旨在揭示MvaT和Rok的DNA结合机理以及自聚合机理，以期增进我们对细菌外源基因抑制因子结构和功能的认识，以辅助研发新的抗菌药物。

In order to adapt new environments, bacteria frequently acquire new genes through horizontal transfer during evolution, such as the acquisition of virulence, antibiotic resistance or novel metabolic capabilities. However, foreign DNA sequences acquired are more likely to decrease rather than increase the fitness of the recipient bacteria. Therefore, many bacteria genera have evolved unique proteins to selectively bind to and silence expression from AT rich regions of the chromosome, which are highly likely acquired from a foreign source. As a result of their activity, xenogeneic silencers are the master regulators of horizontally acquired sequences, including many critical virulence and drug resistance genes in a large number of important bacterial pathogens, such as Mycobacteria tuberculosis, Vibrio cholera, Salmonella typhimurium, enteropathogeneic E. coli, and Pseudomonas aeruginosa. To date, four distinct families of xenogeneic silencers have been identified: H-NS of Proteobacteria, Lsr2 of the Actinomycetes, MvaT of Pseudomonadaceae and Rok of Bacillaceae. We have elucidated that Lsr2 and H-NS recognize AT-rich DNA minor groove through a common AT-hook-like motif, although they are structurally different. Our work on the DNA-binding mechanism of Lsr2 and H-NS were published on PNAS in 2010 and 2011. It is interesting that no AT-hook-like motif is identified for the xenogeneic silencer MvaT and Rok, and their self-oligomerization mechanisms are poorly understood. The object of this study is to reveal the DNA-binding mechanism and oligomerzation mechanism of MvaT and Rok, which will help us to understand the structure-function relationship of these two xenogeneic silencers, as well as provide clues for the development of new antibiotic drugs.