Crystal Structures of the Active and Alloxanthine-Inhibited Forms of Xanthine Dehydrogenase from Rhodobacter capsulatus

• DOI: 10.1016/s0969-2126(01)00697-9
• Publication Date: 2003-01-21T19:54:09Z
• Authors: James J Truglio; Karsten Theis; Silke Leimkühler; Roberto Rappa; K.V Rajagopalan; Caroline Kisker
• Keywords: Xanthine dehydrogenase; Rhodobacter; Hypoxanthine; Xanthine; Allopurinol

Xanthine dehydrogenase (XDH), a complex molybdo/iron-sulfur/flavoprotein, catalyzes the oxidation of hypoxanthine to xanthine followed by oxidation of xanthine to uric acid with concomitant reduction of NAD+. The 2.7 A resolution structure of Rhodobacter capsulatus XDH reveals that the bacterial and bovine XDH have highly similar folds despite differences in subunit composition. The NAD+ binding pocket of the bacterial XDH resembles that of the dehydrogenase form of the bovine enzyme rather than that of the oxidase form, which reduces O(2) instead of NAD+. The drug allopurinol is used to treat XDH-catalyzed uric acid build-up occurring in gout or during cancer chemotherapy. As a hypoxanthine analog, it is oxidized to alloxanthine, which cannot be further oxidized but acts as a tight binding inhibitor of XDH. The 3.0 A resolution structure of the XDH-alloxanthine complex shows direct coordination of alloxanthine to the molybdenum via a nitrogen atom. These results provide a starting point for the rational design of new XDH inhibitors.