The CorA/Mrs2 family of pentameric proteins are cardinal for the influx of Mg²⁺ across cellular membranes, importing the cation to mitochondria in eukaryotes. Yet, the conducting and regulation mechanisms of permeation remain elusive, particularly for the eukaryotic Mrs2 members. Here, we report closed and open Mrs2 cryo-electron microscopy structures, accompanied by functional characterization. Mg²⁺ flux is permitted by a narrow pore, gated by methionine and arginine residues in the closed state. Transition between the conformations is orchestrated by two pairs of conserved sensor-serving Mg²⁺-binding sites in the mitochondrial matrix lumen, located in between monomers. At lower levels of Mg²⁺, these ions are stripped, permitting an alternative, symmetrical shape, maintained by the RDLR motif that replaces one of the sensor site pairs in the open conformation. Thus, our findings collectively establish the molecular basis for selective Mg²⁺ influx of Mrs2 and an auto-ligand-gating regulation mechanism.

五聚体蛋白的 CorA/Mrs2 家族是 Mg²⁺ 穿过细胞膜流入的主要因素，将阳离子输入真核生物的线粒体。然而，渗透的传导和调节机制仍然难以捉摸，特别是对于真核生物 Mrs2 成员。在这里，我们报告了封闭和开放的 Mrs2 冷冻电子显微镜结构，并附有功能表征。Mg²⁺ 助焊剂由窄孔允许，在闭合状态下由蛋氨酸和精氨酸残基门控。构象之间的转换由位于单体之间的线粒体基质管腔中的两对保守的传感器服务 Mg²⁺ 结合位点协调。在较低水平的 Mg²⁺ 中，这些离子被剥离，允许由替代的对称形状，由 RDLR 基序维持，该基序取代了开放构象中的传感器位点对之一。因此，我们的研究结果共同确立了 Mrs2 选择性 Mg²⁺ 内流的分子基础和自配体门控调节机制。