Figure 1: High-resolution crystal structure of MgtE-TMD.

(a) The full-length MgtE dimer (PDB ID 2ZY9) reported previously¹⁶ is viewed in the plane of the membrane, highlighting the N domain (blue), CBS domain (green), plug helix (yellow) and pore forming helices, TM2, TM5 and L1 (red), and other helices of TM5 (orange) in one subunit. The other subunit is coloured cyan. (b) The high-resolution structure of the MgtE-TMD dimer bound to Mg²⁺. The rectangles indicate the divalent cation-binding sites. The overall structure is in the closed conformation. (c,d) Stereo view around TM5 (c) and TM2 (d) of the M1 site, with the 2mF_o−DF_c electron density map contoured at 4.0 σ. The coordinate and hydrogen bonds are depicted by solid and dashed lines, respectively. Water molecules and Mg²⁺ ions are represented by red and orange spheres, respectively.