Figure 2.

Overall structure and docking of paeonolide into BlArap42B. A, top view along the axis of the BlArap42B trimer with docked paeonolide shown as spheres in one of the three active sites. B, active site residues of BlArap42B shown with docked paeonolide. The Arap moiety binds at subsite −1 with distances of 3.3 Å between the catalytic nucleophile Glu³¹¹ and the anomeric carbon, and 2.9 Å between the catalytic acid/base Glu¹⁵¹ and the glycosidic oxygen. Glcp participates in an aromatic stacking interaction with the proposed subsite +1 platform Trp²⁵² and C4-OH hydrogen bonds to Asp²⁴⁹. Paeonolide in this conformation can form an intramolecular hydrogen bond between its acetyl oxygen and C2-OH of the Glcp. The neighboring monomer participates in determining the substrate specificity by Phe⁴²¹ engaged in aromatic stacking with the phenyl group of paeonolide at a possible subsite +2.