A structure-based catalytic mechanism for the xanthine oxidase family of molybdenum enzymes

Robert Huber, Peter Hof, Rui O. Duarte, Jose J. G. Moura, Isabel Moura, Ming Yih Liu, Jean LeGall, Russ Hille, Margarida Archer, Maria J. Romão

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The crystal structure of the xanthine oxidase-related molybdenum-iron protein aldehyde oxidoreductase from the sulfate reducing anaerobic Gram- negative bacterium Desulfovibrio gigas (Mop) was analyzed in its desulfo-, sulfo-, oxidized, reduced, and alcohol-bound forms at 1.8-Å resolution. In the sulfo-form the molybdenum molybdopterin cytosine dinucleotide cofactor has a dithiolenebound fac-[Mo, =O, =S, ···(OH2)] substructure. Bound inhibitory isopropanol in the inner compartment of the substrate binding tunnel is a model for the Michaelis complex of the reaction with aldehydes (H-C=O, -R). The reaction is proposed to proceed by transfer of the molybdenum-bound water molecule as OH- after proton transfer to Glu-869 to the carbonyl carbon of the substrate in concert with hydride transfer to the sulfido group to generate [MoIV, =O, -SH, ···(O-C=O, -R)). Dissociation of the carboxylic acid product may be facilitated by transient binding of Glu- 869 to the molybdenum. The metal-bound water is replenished from a chain of internal water molecules. A second alcohol binding site in the spacious outer compartment may cause the strong substrate inhibition observed. This compartment is the putative binding site of large inhibitors of xanthine oxidase.

Original languageEnglish
Pages (from-to)8846-8851
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number17
Publication statusPublished - 20 Aug 1996


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