Université de Lyon, INSA Lyon, F-69621 Villeurbanne, France.
J Bacteriol. 2011 Aug;193(15):3785-93. doi: 10.1128/JB.05032-11. Epub 2011 Jun 10.
Nickel and cobalt are both essential trace elements that are toxic when present in excess. The main resistance mechanism that bacteria use to overcome this toxicity is the efflux of these cations out of the cytoplasm. RND (resistance-nodulation-cell division)- and MFS (major facilitator superfamily)-type efflux systems are known to export either nickel or cobalt. The RcnA efflux pump, which belongs to a unique family, is responsible for the detoxification of Ni and Co in Escherichia coli. In this work, the role of the gene yohN, which is located downstream of rcnA, is investigated. yohN is cotranscribed with rcnA, and its expression is induced by Ni and Co. Surprisingly, in contrast to the effect of deleting rcnA, deletion of yohN conferred enhanced resistance to Ni and Co in E. coli, accompanied by decreased metal accumulation. We show that YohN is localized to the periplasm and does not bind Ni or Co ions directly. Physiological and genetic experiments demonstrate that YohN is not involved in Ni import. YohN is conserved among proteobacteria and belongs to a new family of proteins; consequently, yohN has been renamed rcnB. We show that the enhanced resistance of rcnB mutants to Ni and Co and their decreased Ni and Co intracellular accumulation are linked to the greater efflux of these ions in the absence of rcnB. Taken together, these results suggest that RcnB is required to maintain metal ion homeostasis, in conjunction with the efflux pump RcnA, presumably by modulating RcnA-mediated export of Ni and Co to avoid excess efflux of Ni and Co ions via an unknown novel mechanism.
镍和钴都是必需的微量元素，过量存在时会有毒性。细菌克服这种毒性的主要耐药机制是将这些阳离子从细胞质中排出。已知 RND（耐药性-结节细胞分裂）和 MFS（主要促进剂超家族）型外排系统可以输出镍或钴。属于独特家族的 RcnA 外排泵负责大肠杆菌中 Ni 和 Co 的解毒。在这项工作中，研究了位于 rcnA 下游的基因 yohN 的作用。yohN 与 rcnA 共转录，其表达受 Ni 和 Co 的诱导。令人惊讶的是，与删除 rcnA 的效果相反，删除 yohN 赋予大肠杆菌对 Ni 和 Co 的抗性增强，同时金属积累减少。我们表明 YohN 定位于周质，并且不直接结合 Ni 或 Co 离子。生理和遗传实验表明 YohN 不参与 Ni 进口。YohN 在变形菌中保守，属于新的蛋白质家族；因此，yohN 已更名为 rcnB。我们表明 rcnB 突变体对 Ni 和 Co 的抗性增强以及它们对 Ni 和 Co 的细胞内积累减少与这些离子在没有 rcnB 的情况下更大的外排有关。总之，这些结果表明 RcnB 与外排泵 RcnA 一起需要维持金属离子的体内平衡，可能通过调节 RcnA 介导的 Ni 和 Co 的外排来避免通过未知的新机制过量排出 Ni 和 Co 离子。
