Figure 2.

Stereoview of the Cd²⁺ binding site (orange) on the RC from Rb. sphaeroides. The six Cd²⁺ ligands are His-H126, His-H128, Asp-H124 (green), and three water molecules (red). Two nearby aspartic acid residues, Asp-L210 (yellow) and Asp-M17 (blue), are part of a hydrogen bonding network that leads from the metal site to Q_B⨪ (see Fig. 5). |F_o| − |F_c| difference electron density (purple) is contoured at 2.5σ and superimposed on the structure. To reduce phase bias, ligands were excluded in the calculation of the map.