Structure and pharmacophoric conformation of 21-BD.

(A) Chemical structure of ouabain, digoxin, and 21-BD. (B) Left: whole structure of Na,K-ATPase (PDB: 4HYT) showed in solid ribbon representation, where the alpha-helix, beta-sheets and turns are in red, blue and gray, respectively; right: highlight of the binding site with ouabain shown in tube representation. Dashed red lines indicate hydrogen bonds. Only polar hydrogen atoms were showed for a better visualization. Pharmacophoric conformation of, (C) digoxin and (D) 21-BD; polar and nonpolar interactions are depicted by magenta and green colors, respectively. Dashed lines indicate hydrogen bonds. Residue interactions are color coded as indicated in the inserted scale.