Molecular basis of Mg(2+) permeation through the human mitochondrial Mrs2 channel

Mitochondrial RNA splicing 2 (Mrs2), a eukaryotic CorA ortholog, enables Mg(2+) to permeate the inner mitochondrial membrane and plays an important role in mitochondrial metabolic function. However, the mechanism by which Mrs2 permeates Mg(2+) remains unclear. Here, we report four cryo-electron microscopy (cryo-EM) reconstructions of Homo sapiens Mrs2 (hMrs2) under various conditions. All of these hMrs2 structures form symmetrical pentamers with very similar pentamer and protomer conformations. A special structural feature of Cl(−)-bound R-ring, which consists of five Arg332 residues, was found in the hMrs2 structure. Molecular dynamics simulations and mitochondrial Mg(2+) uptake assays show that the R-ring may function as a charge repulsion barrier, and Cl(−) may function as a ferry to jointly gate Mg(2+) permeation in hMrs2. In addition, the membrane potential is likely to be the driving force for Mg(2+) permeation. Our results provide insights into the channel assembly and Mg(2+) permeation of hMrs2.