SitABCD is the alkaline Mn2+ transporter of Salmonella enterica serovar typhimurium
SitABCD is the alkaline Mn2+ transporter of Salmonella enterica serovar typhimurium
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DOI：
10.1128/jb.184.12.3159-3166.2002
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发表时间：
2002-06-01
影响因子：
3.2
通讯作者：
Maguire, ME
中科院分区：
文献类型：
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作者：
Kehres, DG;Janakiraman, A;Maguire, ME
MntH是哺乳动物天然耐药相关巨噬细胞蛋白1（Nramp 1）的细菌同系物，是肠道沙门氏菌鼠伤寒血清型和大肠杆菌的主要Mn 2+转运蛋白。S.肠血清型鼠伤寒沙门氏菌MntH表达对于完全毒力是重要的;然而，携带mntH缺失的菌株仅部分减毒并且没有显示出Mn 2+缺乏的明显迹象。我们注意到mntH和假定的Fe 2+转运蛋白sitABCD的启动子序列似乎具有相同的对Mn 2+响应的调控元件，因此假设sitABCD可以以高亲和力转运Mn 2+。我们现在已经用S.用Mn-54（2+）和Fe-55（2+）对肠道血清型鼠伤寒沙门氏菌（Enterica serovar Typhimurium）进行纯化，并将其性质与MntH的性质进行比较。SitABCD介导Mn 2+的内流，其表观亲和力（K-a）与MntH相同，为0.1 μ M。它也运输Fe 2+，但K-a低30至100倍，为3至10 μ M。Fe ~（2+）对Mn ~（54）（2+）转运的抑制作用和Mn ~（2+）对Fe ~（55）（2+）转运的抑制作用的抑制常数与各阳离子的K-a值相当。由于微摩尔浓度的游离Fe 2+是不可能在生物系统中，我们得出结论，SitABCD功能生理作为Mn 2+转运。SitABCD和MntH的阳离子抑制曲线对于两种结构和能量不相关的转运蛋白来说惊人地相似，Cd 2 + Ki约为1 μ M，Co 2 + Ki约为20 μ M，Ni 2+，Cu 2+，而Fe ~（3+）仅在浓度>0.1 mM时抑制这两种转运蛋白。一个区别是Zn ~（2+）表现出对SitABCD的有效抑制（K-i = 1至3 μ M），但对MntH的抑制较弱（K-i > 50 μ M）。我们以前已经表明，MntH运输Mn 2+在酸性条件下最有效。与此形成鲜明对比的是，SitABCD在酸性pH下几乎没有转运能力，在弱碱性pH下转运Mn 2+最佳。总的来说，再加上证据表明，每个转运蛋白是多重的，但在转录水平上明显的调节，不同的运输特性MntH与SitABCD表明，每个转运蛋白可能是专门的Mn 2+吸收在不同的生理环境。
MntH, a bacterial homolog of the mammalian natural resistance-associated macrophage protein 1 (Nramp1), is a primary Mn2+ transporter of Salmonella enterica serovar Typhimurium and Escherichia coli. S. enterica serovar Typhimurium MntH expression is important for full virulence; however, strains carrying an mntH deletion are only partially attenuated and display no obvious signs of Mn2+ deficiency. We noted that promoter sequences for mntH and for the putative Fe2+ transporter sitABCD appeared to have the same regulatory element responsive to Mn2+ and so hypothesized that sitABCD could transport Mn2+ with high affinity. We have now characterized transport by SitABCD in S. enterica serovar Typhimurium using Mn-54(2+) and Fe-55(2+) and compared its properties to those of MntH. SitABCD mediates the influx of Mn2+ with an apparent affinity (K-a) identical to that of MntH, 0.1 muM. It also transports Fe2+ but with a K-a 30 to 100 times lower, 3 to 10 muM. Inhibition of Mn-54(2+) transport by Fe2+ and of Fe-55(2+) transport by Mn2+ gave inhibition constants comparable to each cation's K-a for influx. Since micromolar concentrations of free Fe2+ are improbable in a biological system, we conclude that SitABCD functions physiologically as a Mn2+ transporter. The cation inhibition profiles of SitABCD and MntH are surprisingly similar for two structurally and energetically unrelated transporters, with a Cd2+ K-i of approximate to1 muM and a Co2+ K-i of approximate to20 muM and with Ni2+, Cu2+, and Fe3+ inhibiting both transporters only at concentrations of >0.1 mM. The one difference is that Zn2+ exhibits potent inhibition of SitABCD (K-i = 1 to 3 muM) but inhibits MntH weakly (K-i > 50 muM). We have previously shown that MntH transports Mn2+ Most effectively under acidic conditions. In sharp contrast, SitABCD has almost no transport capacity at acid pHs and optimally transports Mn2+ at slightly alkaline pHs. Overall, coupled with evidence that each transporter is multiply but distinctly regulated at the transcriptional level, the distinct transport properties of MntH versus SitABCD suggest that each transporter may be specialized for Mn2+ uptake in different physiological environments.