FIGURE 8.

Location of metal(loid) binding sites in ArsR/SmtB repressors.Metal(loid) binding sites in members of the ArsR/SmtB family of repressor proteins are shown on a surface model of the CadC aporepressor structure either by coloring CadC residues corresponding to each binding site as identified from the structure-based alignment (Fig. 1A) or, in the case of CmtR, by overlaying the two structures. The S₃ As(III) binding site of the R773 ArsR (red) formed within each monomer overlaps with the corresponding S₄ Cd(II) binding site of CadC (yellow) formed between the N terminus of one subunit and the DNA binding domain of the other subunit. Zn(II) binding sites of CadC and SmtB (cyan) formed between the antiparallel C-terminal α6 helices also overlap. The S₃ binding sites of CgArsR1 (green), CmtR (blue), and AfArsR (purple) are at a variety of locations distributed over the surface of the repressor.