Figure 2: The Zn2+ ion binding site. (A) |Fo| - |Fc| omit map (contoured at 4.5σ) for Zn2+-chelating residues, including Glu338, Cys340, Cys417 and Cys418, and L-Araf (product) and anomalous difference Fourier map (contoured at 12σ) for identifying the location of the Zn2+ ion are shown as green and red color, respectively. (B) The superimposition of the native (colored in green), apo (colored in cyan) and complex structure (colored in magenta) shows that the two Zn2+ ion-binding residues (Cys417 and Cys418) in the apo structure are flipped over in the absence of Zn2+ ion. (C) The superimposition of the apo (colored in cyan) and complex structure (colored in magenta) reveals that the Cys417- and Cys418-containing loop is broken because of lack of Zn2+ion interaction.