FIGURE 2. Structure of SyrB2 with bound iron, chloride and KG.

Iron is shown in brown, chloride in green. a, Stereo view of the SyrB2 structure. Two protein ligands of iron (His 116 and His 235), KG and Arg 248 are shown in stick representation. A disordered loop (residues 56–60) is indicated by the broken line. A detergent molecule (DSU) from the crystallization condition packs along the bottom surface of the structure. b, Stereo view of the SyrB2 active site. A 2F_o - F_c composite omit map contoured to 2 is shown in blue mesh. c, SyrB2 active site distances. d, Dispersive difference Fourier map from bromide-containing crystals, calculated by subtracting data collected at 0.9197 Å (bromide edge) from data collected at 1.7340 Å (iron edge). The purple mesh (+ 4) confirms the location of the halide ion; the brown mesh (- 4) confirms the location of the iron.