Figure 2: Structural snapshots of ZnuD with distinct zinc occupancies.

Side and top structural representations of (a) native ZnuD crystals, (b) ZnuD co-crystallized with cadmium and (c) ZnuD soaked with zinc. The plug domain is coloured gold, the β-barrel domain is represented in blue, the metal-sensing extracellular loop 3 is represented in red, and the co-crystallized detergent molecules are displayed in green and red ball-and-stick representation; the zinc and cadmium ions are illustrated as green and brown spheres, respectively. (d) Close-up view of the peripheral and high-affinity binding sites from the cadmium-bound ZnuD crystal structure. ZnuD is represented in blue with the extracellular loop 3 and the restriction loop coloured in red and green, respectively. Cavities are represented as grey surfaces to illustrate the pathway connecting the peripheral-binding site to the buried high-affinity site. Residues contributing to the high-affinity zinc-binding site are labelled with red broken arrows, and residues from the peripheral cadmium-binding site are labelled using grey arrows.