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Figure 1
UOX catalysis. (a) Reaction scheme for UOX catalysis highlighting the separate oxidation and hydration steps. UOX catalyses the transformation of UA to 5-HIU. The latter is then converted to allantoin either enzymatically or non-enzymatically. (b) Chemical structure of the inhibitor 8-azaxanthine (8AZA) used in this study. (c) Cartoon representation of the ∼137 kDa UOX tetramer with the four protomers highlighted by different colours. Bound ligands are shown as orange sticks with their active site location marked by black rectangles. UOX binds four ligands at independent active sites each contributed by two UOX protomers. Only three are visible in the current view. (d) Stick representation of UA (orange) bound in the active site at the interface between two different UOX protomers, shown in yellow and magenta, respectively. Nitro­gen and oxygen atoms are in blue and red, respectively. Water molecules (W1, W2, Wa) in close proximity to UA are represented by spheres. Hydrogen bonds are shown by cyan broken lines. Residues labelled with an asterisk indicate that they belong to a different UOX protomer. Panels (c) and (d) were generated using coordinates from the anaerobic UOX–UA complex (PDB entry 4d12; Bui et al., 2014BB11). Chemical and molecular graphics representations in this work were produced with CHEMDRAW (Perkin Elmer) and PyMOL (Schrödinger, LLC) (DeLano, 2002BB18), respectively, and assembled using Adobe Illustrator (Adobe).

IUCrJ
Volume 8| Part 1| January 2021| Pages 46-59
ISSN: 2052-2525
https://doi.org/10.1107/S2052252520013615