Figure 4

Binding of pNP-TMP to D163A inactive CpsORN. (A) The active site of unliganded CpsORN contains magnesium ion. The residues located in the active site are presented as a green stick model and bound magnesium ion is presented as a light green sphere. (B) The active site of CpsORN has a negatively charged surface, created by Asp12, Glu14, Asp112, and Asp163. (C) Two molecules of pNP-TMP (lime green) bind to the active site of CpsORN. Notably, D163A inactive CpsORN mutant does not contain a divalent ion, which means that metal ion is not essential for ligand-binding. (D) Stereo view of the atomic interactions between bound pNP-TMP and CpsORN. (E) Conformation changes in the pNP-TMP binding residues are shown by structural superposition of unliganded (green) and pNP-TMP-bound CpsORN (orange) structures.