Figure 2: Mn²⁺ and Ca²⁺ binding sites in MgtE-TMD.

(a) Stereo view of TM5 in the M1 site of the Mn²⁺-bound structure. The anomalous difference Fourier map derived from the Mn-peak data set contoured at 5.0 σ and the 2mF_o−DF_c electron density map contoured at 3.5 σ are shown in magenta and green, respectively. Water molecules and Mn²⁺ ions are represented by red and purple spheres, respectively. (b) Stereo view of TM5 in the M1 site of the Ca²⁺-bound structure, with the 2mF_o−DF_c and mF_o–DF_c electron density maps contoured at 2.5 σ (green) and 3.0 σ (blue), respectively. Ca²⁺ ions are represented by green spheres. (c) Mn²⁺ binding to the M2, M2′ and M3 sites. Water molecules and Mn²⁺ ions are represented by red and purple spheres, respectively. Amino acid residues involved in binding to Mn²⁺ or hydration water molecules are shown in ball and stick representations. The adjacent MgtE-TMD molecule is coloured grey. The 2mF_o−DF_c map (2.5 σ) and anomalous difference Fourier maps (4.5 σ) are shown in green and magenta, respectively. The coordinate and hydrogen bonds are depicted by solid and dashed lines, respectively.