Huang Xiaojuan, Shin Jung-Ho, Pinochet-Barros Azul, Su Tina T, Helmann John D
Cornell University, Department of Microbiology, Ithaca, NY, 14853-8101, USA.
Mol Microbiol. 2017 Jan;103(2):253-268. doi: 10.1111/mmi.13554. Epub 2016 Nov 2.
The Bacillus subtilis MntR metalloregulatory protein senses manganese, an essential element required for central metabolism, oxidative stress resistance and replication. An mntR null mutant is highly sensitive to Mn(II) intoxication, which is attributed in part to the constitutive expression of two importers: the proton-dependent NRAMP family transporter MntH and the ABC transporter MntABCD. Here, we show that an mntR null mutant is still sensitive to Mn(II) intoxication even if both of the import systems are absent. This Mn(II) sensitivity results from the requirement for MntR to activate the transcription of two genes encoding cation diffusion facilitator (CDF) family efflux pumps. Physiological studies indicate that MneP (formerly YdfM) serves as the primary Mn(II) efflux pump with MneS (formerly YeaB) playing a secondary role. Mutant strains lacking mneP are Mn(II) sensitive and accumulate elevated levels of Mn(II), and these effects are exacerbated in a mneP mneS double mutant. DNA-binding and in vitro transcription studies demonstrate that MntR binds to both the mneP and mneS regulatory regions and directly activates transcription in response to levels of Mn(II) several-fold higher than required for repression of import genes. These results highlight the delicate balance of Mn(II) uptake and efflux systems controlled by MntR.
枯草芽孢杆菌MntR金属调节蛋白可感知锰，锰是中心代谢、抗氧化应激和复制所必需的元素。mntR基因缺失突变体对Mn(II)中毒高度敏感，这部分归因于两种锰转运蛋白的组成型表达：质子依赖性天然抗性相关巨噬蛋白（NRAMP）家族转运蛋白MntH和ABC转运蛋白MntABCD。在此，我们表明，即使两种锰导入系统均缺失，mntR基因缺失突变体对Mn(II)中毒仍敏感。这种对Mn(II)的敏感性源于MntR激活两个编码阳离子扩散促进因子（CDF）家族外排泵的基因转录的需求。生理学研究表明，MneP（以前称为YdfM）作为主要的Mn(II)外排泵，而MneS（以前称为YeaB）起次要作用。缺乏mneP的突变菌株对Mn(II)敏感且积累的Mn(II)水平升高，并且这些效应在mneP mneS双突变体中加剧。DNA结合和体外转录研究表明，MntR与mneP和mneS的调控区域结合，并响应比抑制导入基因所需水平高几倍的Mn(II)水平直接激活转录。这些结果突出了由MntR控制的Mn(II)摄取和外排系统的微妙平衡。
