Metal binding by the 3mPHP mutant. (A) Detail of the 3mPHP active site showing two peaks on the anomalous difference map contoured at 3.5 sigma shown in green. The two modelled Zn2+ ions are shown as spheres. Yellow dashed lines represent the distance (2.0 to 2.1 Å) between the side chains of the metal-binding residues and the centre of the two peaks. The (B) X-ray fluorescence scan of a zinc standard solution (grey) and of a 3mPHP protein sample (purple).