Predicted binding of coumestrol, curcumin and aristolochic acid I in the ATP binding site of CK2. The binding mode of coumestrol (A), curcumin (B), and aristolochic acid 1 (C) in the active site of CK2 was predicted by docking. The three compounds (carbon atoms colored in orange) and an ATP analog, phosphoaminophosphonic acid-adenylate ester (carbon atoms colored in yellow), were overlayed together. The docked pose indicated that hydrogen bonds were formed between coumestrol and CK2. Hydrogen bonds are labeled in green dotted lines. CK2 residues adjacent to coumestrol Glu114, Val116, Lys68, and a conserved water molecule, are shown in line representation along with coumestrol (in A), curcumin (in B), or aristolochic acid 1 (in C) (red represents oxygen, blue represents nitrogen and white represents hydrogen). The rest of the CK2 protein is shown in the flat ribbon. (D). Summary of interactions of coumestrol, curcumin and aristolochic acid I with CK2. Residues that make H-bonds, LibDockScore and IC50 values of the three inhibitors were listed.