Fig. 6.

Common pharmacophores of colchicine and PAB, based on docking studies. A. Docked pose of PAB in the colchicine site, superimposed onto that of colchicine derived from the 1SA0 crystal structure [5]. Tubulin is rendered in ribbon, with amino acids within 4 Å shown as thin sticks. Hydrogen bonding amino acids are depicted as thick sticks, with carbon atoms from the α- and β-subunits colored purple and grey, respectively. Hydrogen bonds are highlighted by yellow dashed lines. PAB and colchicine are shown in stick with carbon atoms colored green and brown for PAB and colchicine, respectively. The α-tubulin backbone is tinted light purple, while the β-tubulin backbone is grey. Helices are shown as thick ribbons, and β-sheets as thin strands. Nitrogen atoms are blue, oxygen red, and sulfur yellow. Tubulin hydrogen atoms are white, while those of colchicine and PAB are not shown. B. Binding conformations of colchicine and PAB extracted from the models. Colors as in Panel A. Corresponding pharmacophoric features, as discussed in the text, are indicated. Hydrogen bond acceptors and hydrophobic features are shown as red and blue dashed circles, respectively.