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PDBsum entry 2a9c
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Oxidoreductase
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PDB id
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2a9c
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References listed in PDB file
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Key reference
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Title
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Structural insights into sulfite oxidase deficiency.
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Authors
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E.Karakas,
H.L.Wilson,
T.N.Graf,
S.Xiang,
S.Jaramillo-Busquets,
K.V.Rajagopalan,
C.Kisker.
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Ref.
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J Biol Chem, 2005,
280,
33506-33515.
[DOI no: ]
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PubMed id
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Abstract
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Sulfite oxidase deficiency is a lethal genetic disease that results from defects
either in the genes encoding proteins involved in molybdenum cofactor
biosynthesis or in the sulfite oxidase gene itself. Several point mutations in
the sulfite oxidase gene have been identified from patients suffering from this
disease worldwide. Although detailed biochemical analyses have been carried out
on these mutations, no structural data could be obtained because of problems in
crystallizing recombinant human and rat sulfite oxidases and the failure to
clone the chicken sulfite oxidase gene. We synthesized the gene for chicken
sulfite oxidase de novo, working backward from the amino acid sequence of the
native chicken liver enzyme by PCR amplification of a series of 72 overlapping
primers. The recombinant protein displayed the characteristic absorption
spectrum of sulfite oxidase and exhibited steady state and rapid kinetic
parameters comparable with those of the tissue-derived enzyme. We solved the
crystal structures of the wild type and the sulfite oxidase deficiency-causing
R138Q (R160Q in humans) variant of recombinant chicken sulfite oxidase in the
resting and sulfate-bound forms. Significant alterations in the
substrate-binding pocket were detected in the structure of the mutant, and a
comparison between the wild type and mutant protein revealed that the active
site residue Arg-450 adopts different conformations in the presence and absence
of bound sulfate. The size of the binding pocket is thereby considerably
reduced, and its position relative to the cofactor is shifted, causing an
increase in the distance of the sulfur atom of the bound sulfate to the
molybdenum.
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Figure 4.
FIGURE 4. Superposition of the active sites of the sulfate
bound (yellow) and unbound rCSO (gray). Only the Moco of the
sulfate free structure is shown. The molybdenum is shown in
green, and the water/hydroxo ligand is shown as a red sphere.
Hydrogen bonds between the sulfate and Arg-450 are shown with
dashed lines.
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Figure 8.
FIGURE 8. Proposed reaction mechanism for sulfite oxidase.
Schematic presentation of the reaction mechanism for the
oxidation of sulfite to sulfate. A, oxidized Mo center. B, the
Mo(IV)-sulfate adduct formed after an attack of sulfite on the
equatorial oxo group. C, the free reduced Mo(IV) center after
release of sulfate.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2005,
280,
33506-33515)
copyright 2005.
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