Complexed and ligand-free high-resolution structures of urate oxidase (Uox) from Aspergillus flavus: a reassignment of the active-site binding mode.

High-resolution X-ray structures of the complexes of Aspergillus flavus urate oxidase (Uox) with three inhibitors, 8-azaxanthin (AZA), 9-methyl uric acid (MUA) and oxonic acid (OXC), were determined in an orthorhombic space group (I222). In addition, the ligand-free enzyme was also crystallized in a monoclinic form (P2(1)) and its structure determined. Higher accuracy in the three new enzyme-inhibitor complex structures (Uox-AZA, Uox-MUA and Uox-OXC) with respect to the previously determined structure of Uox-AZA (PDB code 1uox) leads to a reversed position of the inhibitor in the active site of the enzyme. The corrected anchoring of the substrate (uric acid) allows an improvement in the understanding of the enzymatic mechanism of urate oxidase.