Metal ion homeostasis is important for healthy cell function and is regulated by metal ion transporters and chaperones. To explore metal ion binding to membrane transport proteins we have used cadmium-113 as a solid state NMR probe of the Escherichia coli zinc exporter ZitB present in native membrane preparations. Competition experiments with other metal ions indicated that nickel and copper are also able to bind to this protein. Metal ion uptake studies were also performed using ZitB-reconstituted into proteoliposomes for a well established fluorescence assay. The results of both the solid state NMR and the uptake studies demonstrate that ZitB is potentially capable of transporting not only zinc but also cadmium, nickel and copper. The solid state NMR approach therefore offers great potential for defining the substrate spectrum of metal ion transporter proteins in their native membrane environments. Further, it should be useful for functional dissection of transporter mechanisms by facilitating the identification of functional residues by mutational studies.

中文翻译：

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通过固态NMR探测金属离子底物与天然膜中大肠杆菌ZitB出口子的结合。

金属离子稳态对健康的细胞功能很重要，并且受金属离子转运蛋白和伴侣的调节。为了探索金属离子与膜转运蛋白的结合，我们使用镉113作为天然膜制剂中存在的大肠杆菌锌出口蛋白ZitB的固态NMR探针。与其他金属离子的竞争实验表明，镍和铜也能够与该蛋白质结合。还使用重组为蛋白脂质体的ZitB进行了金属离子吸收研究，以建立完善的荧光测定法。固态NMR和吸收研究的结果均表明ZitB不仅能够转运锌，而且还能够转运镉，镍和铜。因此，固态NMR方法为在其天然膜环境中定义金属离子转运蛋白的底物光谱提供了巨大潜力。此外，通过促进突变研究鉴定功能残基，对转运蛋白的功能解剖应该是有用的。