Department of Biochemistry, University of Zurich, Zurich, Switzerland.
Elife. 2022 Jan 10;11:e74589. doi: 10.7554/eLife.74589.
Members of the ubiquitous SLC11/NRAMP family catalyze the uptake of divalent transition metal ions into cells. They have evolved to efficiently select these trace elements from a large pool of Ca and Mg, which are both orders of magnitude more abundant, and to concentrate them in the cytoplasm aided by the cotransport of H serving as energy source. In the present study, we have characterized a member of a distant clade of the family found in prokaryotes, termed NRMTs, that were proposed to function as transporters of Mg. The protein transports Mg and Mn but not Ca by a mechanism that is not coupled to H. Structures determined by cryo-EM and X-ray crystallography revealed a generally similar protein architecture compared to classical NRAMPs, with a restructured ion binding site whose increased volume provides suitable interactions with ions that likely have retained much of their hydration shell.
普遍存在的 SLC11/NRAMP 家族成员可催化二价过渡金属离子进入细胞。它们的进化是为了从大量的 Ca 和 Mg 中有效地选择这些痕量元素，而 Ca 和 Mg 的丰度要高几个数量级，并且在 H 共转运的帮助下，将它们浓缩在细胞质中，H 共转运作为能量来源。在本研究中，我们对一种在原核生物中发现的、属于家族中一个遥远分支的成员进行了特征描述，该成员被称为 NRMT，其被提议作为 Mg 的转运蛋白。该蛋白通过不与 H 偶联的机制运输 Mg 和 Mn，但不运输 Ca。通过低温电子显微镜和 X 射线晶体学确定的结构显示，与经典的 NRAMP 相比，其具有一般相似的蛋白质结构，离子结合位点发生了重构，其增加的体积与可能保留了大部分水合壳的离子提供了合适的相互作用。
