3NRZ

Crystal Structure of Bovine Xanthine Oxidase in Complex with Hypoxanthine

Summary for 3NRZ

• Entry DOI: 10.2210/pdb3nrz/pdb
• Related: 3b9j 3etr 3eub
• Descriptor: Xanthine dehydrogenase/oxidase, FE2/S2 (INORGANIC) CLUSTER, FLAVIN-ADENINE DINUCLEOTIDE, ... (9 entities in total)
• Functional Keywords: xanthine oxidase, hypoxanthine, substrate orientation, hydroxylase, oxidoreductase
• Biological source: Bos taurus (bovine,cow,domestic cattle,domestic cow); More
• Cellular location: Cytoplasm (By similarity): P80457 P80457 P80457
• Total number of polymer chains: 6
• Total formula weight: 273905.04

Authors

Cao, H.,Pauff, J.M.,Hille, R. (deposition date: 2010-07-01, release date: 2010-07-14, Last modification date: 2023-12-27)

Primary citation

Cao, H.,Pauff, J.M.,Hille, R.
Substrate orientation and catalytic specificity in the action of xanthine oxidase: the sequential hydroxylation of hypoxanthine to uric acid.
J.Biol.Chem., 285:28044-28053, 2010

PubMed Abstract: Xanthine oxidase is a molybdenum-containing enzyme catalyzing the hydroxylation of a sp(2)-hybridized carbon in a broad range of aromatic heterocycles and aldehydes. Crystal structures of the bovine enzyme in complex with the physiological substrate hypoxanthine at 1.8 A resolution and the chemotherapeutic agent 6-mercaptopurine at 2.6 A resolution have been determined, showing in each case two alternate orientations of substrate in the two active sites of the crystallographic asymmetric unit. One orientation is such that it is expected to yield hydroxylation at C-2 of substrate, yielding xanthine. The other suggests hydroxylation at C-8 to give 6,8-dihydroxypurine, a putative product not previously thought to be generated by the enzyme. Kinetic experiments demonstrate that >98% of hypoxanthine is hydroxylated at C-2 rather than C-8, indicating that the second crystallographically observed orientation is significantly less catalytically effective than the former. Theoretical calculations suggest that enzyme selectivity for the C-2 over C-8 of hypoxanthine is largely due to differences in the intrinsic reactivity of the two sites. For the orientation of hypoxanthine with C-2 proximal to the molybdenum center, the disposition of substrate in the active site is such that Arg(880) and Glu(802), previous shown to be catalytically important for the conversion of xanthine to uric acid, play similar roles in hydroxylation at C-2 as at C-8. Contrary to the literature, we find that 6,8-dihydroxypurine is effectively converted to uric acid by xanthine oxidase.

PubMed: 20615869
DOI: 10.1074/jbc.M110.128561

Experimental method

X-RAY DIFFRACTION (1.8 Å)