Shin Minsang
Department of Microbiology, Kyungpook National University School of Medicine, 680 Gukchaebosang-Ro, Jung-gu, Daegu, 41944, South Korea.
Biochem Biophys Res Commun. 2017 Jan 29;483(1):392-396. doi: 10.1016/j.bbrc.2016.12.132. Epub 2016 Dec 21.
Secretion of effector proteins in Enteropathogeneic Escherichia coli (EPEC) and Enterohemorrhagic Escherichia coli (EHEC) is mediated by a specialized type III secretion system, components of which are encoded in the LEE operons 1 to 5. H-NS, a global repressor in E. coli, silences the expression of LEE operons. Ler, a master regulator in LEE operons, shares 24% amnio acid identity and 44% amino acid similarity to H-NS. Interestingly, rather than a gene silencer, its main role has been characterized as an antagonizing protein that relieves H-NS-mediated transcriptional silencing. In the previous study we reported molecular mechanism for the repression of LEE5 promoter in EPEC and EHEC by H-NS as a protein interaction between upstream DNA-bound H-NS and the αCTD of promoter-bound RNA polymerase. The mechanism underlying Ler-mediated alleviation of the genes repression by H-NS is largely unknown. We examined regulatory effect of these proteins on LEE5p activity using various in vitro tools. Our results revealed that binding affinity of Ler to the LEE5p DNA is about 40 folds greater than that of H-NS as determined by surface plasmon resonance. We verified that Ler binding removed H-NS bound to the same stretch of DNA on LEE5 promoter resulting in a derepression.
肠致病性大肠杆菌（EPEC）和肠出血性大肠杆菌（EHEC）中效应蛋白的分泌由一种特殊的III型分泌系统介导，该系统的组分由LEE操纵子1至5编码。H-NS是大肠杆菌中的一种全局阻遏物，可使LEE操纵子的表达沉默。Ler是LEE操纵子中的主要调节因子，与H-NS的氨基酸同一性为24%，氨基酸相似性为44%。有趣的是，与其作为基因沉默子的作用不同，其主要作用已被确定为一种拮抗蛋白，可解除H-NS介导的转录沉默。在之前的研究中，我们报道了H-NS抑制EPEC和EHEC中LEE5启动子的分子机制，即上游结合DNA的H-NS与启动子结合的RNA聚合酶的αCTD之间的蛋白质相互作用。Ler介导的H-NS对基因抑制的缓解机制在很大程度上尚不清楚。我们使用各种体外工具研究了这些蛋白质对LEE5p活性的调节作用。我们的结果表明，通过表面等离子体共振测定，Ler与LEE5p DNA的结合亲和力比H-NS高约40倍。我们证实，Ler的结合去除了与LEE5启动子上同一段DNA结合的H-NS，从而导致去抑制。
