Université d'Avignon et des Pays de Vaucluse, UMR408, Sécurité et Qualité des Produits d'Origine Végétale, F-84000, Avignon, France.
BMC Microbiol. 2012 Jun 25;12:125. doi: 10.1186/1471-2180-12-125.
Bacillus cereus is a facultative anaerobe that causes diarrheal disease in humans. Diarrheal syndrome may result from the secretion of various virulence factors including hemolysin BL and nonhemolytic enterotoxin Nhe. Expression of genes encoding Hbl and Nhe is regulated by the two redox systems, ResDE and Fnr, and the virulence regulator PlcR. B. cereus Fnr is a member of the Crp/Fnr family of iron-sulfur (Fe-S) proteins. Only its apo-form has so far been studied. A major goal in deciphering the Fnr-dependent regulation of enterotoxin genes is thus to obtain and characterize holoFnr.
Fnr has been subjected to in vitro Fe-S cluster reconstitution under anoxic conditions. UV-visible and EPR spectroscopic analyses together with the chemical estimation of the iron content indicated that Fnr binds one [4Fe-4S]2+ cluster per monomer. Atmospheric O2 causes disassembly of the Fe-S cluster, which exhibited a half-life of 15 min in air. Holo- and apoFnr have similar affinities for the nhe and hbl promoter regions, while holoFnr has a higher affinity for fnr promoter region than apoFnr. Both the apo- and holo-form of Fnr interact with ResD and PlcR to form a ternary complex.
Overall, this work shows that incorporation of the [4Fe-4S]2+ cluster is not required for DNA binding of Fnr to promoter regions of hbl and nhe enterotoxin genes or for the formation of a ternary complex with ResD and PlcR. This points to some new unusual properties of Fnr that may have physiological relevance in the redox regulation of enterotoxin gene regulation.
蜡样芽胞杆菌是一种兼性厌氧菌，可导致人类腹泻病。腹泻综合征可能是由各种毒力因子的分泌引起的，包括溶血素 BL 和非溶血肠毒素 Nhe。编码 Hbl 和 Nhe 的基因的表达受两个氧化还原系统 ResDE 和 Fnr 以及毒力调节因子 PlcR 调节。B. cereus Fnr 是 Crp/Fnr 家族的铁硫 (Fe-S) 蛋白成员。迄今为止，仅研究了其脱辅基形式。因此，阐明 Fnr 依赖性肠毒素基因调控的主要目标是获得和表征全酶 Fnr。
Fnr 已在缺氧条件下进行体外 Fe-S 簇的重建。紫外可见和 EPR 光谱分析以及铁含量的化学估算表明，Fnr 每个单体结合一个 [4Fe-4S]2+簇。大气 O2 会导致 Fe-S 簇解体，其在空气中的半衰期为 15 分钟。全酶和脱辅基 Fnr 与 nhe 和 hbl 启动子区域具有相似的亲和力，而全酶 Fnr 对 fnr 启动子区域的亲和力高于脱辅基 Fnr。脱辅基和全酶 Fnr 都与 ResD 和 PlcR 相互作用形成三元复合物。
总的来说，这项工作表明，[4Fe-4S]2+簇的掺入对于 Fnr 与 hbl 和 nhe 肠毒素基因启动子区域的 DNA 结合或与 ResD 和 PlcR 形成三元复合物不是必需的。这表明 Fnr 具有一些新的不寻常特性，这可能在肠毒素基因调控的氧化还原调节中具有生理相关性。
