A structure-based catalytic mechanism for the xanthine oxidase family of molybdenum enzymes.
The crystal structure of the xanthine oxidase-related molybdenum-iron protein aldehyde oxido-reductase 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-A resolution. In the sulfo-form the molybdenum molybdopterin cytosine dinucleotide cofactor has a dithiolene-bound 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.
Huber
R
R
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Hof
P
P
Duarte
R O
RO
Moura
J J
JJ
Moura
I
I
Liu
M Y
MY
LeGall
J
J
Hille
R
R
Archer
M
M
Romão
M J
MJ
D000445:Aldehyde Oxidoreductases / Q000737:chemistry / Q000145:classification / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D003597:Cytosine Nucleotides / Q000737:chemistry; D003901:Desulfovibrio / Q000201:enzymology*; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D011622:Pterins / Q000737:chemistry; D014969:Xanthine Oxidase / Q000737:chemistry* / Q000145:classification / Q000378:metabolism
D001426:Bacterial Proteins; D003597:Cytosine Nucleotides; D011622:Pterins; C066895:molybdopterin cytosine dinucleotide; D008982:Molybdenum; D014969:Xanthine Oxidase; D000445:Aldehyde Oxidoreductases; C101459:Mop protein, Desulfovibrio gigas