FIG. 3.
Location of the type 2 metal binding sites. The two type 2 metal binding sites in each monomer are formed at the interface of the α6 and α6′ helices in each dimer. The asymmetry in the distribution of zinc is shown for the two dimers in the asymmetric unit. (A) Dimera has zinc (purple spheres) bound at both ends of the dimer interface via side chain ligands arranged tetrahedrally (donated by the side chains of Asp-101 and His-103 of one monomer [green] and His-114 and Glu-117 of the other monomer [magenta]). (B) Dimerb has only a single bound zinc, because the second type 2 site is more disordered, and Glu117 is not visible in the structure.