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PDBsum entry 1v8x
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Oxidoreductase
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PDB id
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1v8x
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Crystal structure of the dioxygen-Bound heme oxygenase from corynebacterium diphtheriae: implications for heme oxygenase function.
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Authors
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M.Unno,
T.Matsui,
G.C.Chu,
M.Couture,
T.Yoshida,
D.L.Rousseau,
J.S.Olson,
M.Ikeda-Saito.
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Ref.
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J Biol Chem, 2004,
279,
21055-21061.
[DOI no: ]
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PubMed id
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Abstract
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HmuO, a heme oxygenase of Corynebacterium diphtheriae, catalyzes degradation of
heme using the same mechanism as the mammalian enzyme. The oxy form of HmuO, the
precursor of the catalytically active ferric hydroperoxo species, has been
characterized by ligand binding kinetics, resonance Raman spectroscopy, and
x-ray crystallography. The oxygen association and dissociation rate constants
are 5 microm(-1) s(-1) and 0.22 s(-1), respectively, yielding an O(2) affinity
of 21 microm(-1), which is approximately 20 times greater than that of mammalian
myoglobins. However, the affinity of HmuO for CO is only 3-4-fold greater than
that for mammalian myoglobins, implying the presence of strong hydrogen bonding
interactions in the distal pocket of HmuO that preferentially favor O(2)
binding. Resonance Raman spectra show that the Fe-O(2) vibrations are tightly
coupled to porphyrin vibrations, indicating the highly bent Fe-O-O geometry that
is characteristic of the oxy forms of heme oxygenases. In the crystal structure
of the oxy form the Fe-O-O angle is 110 degrees, the O-O bond is pointed toward
the heme alpha-meso-carbon by direct steric interactions with Gly-135 and
Gly-139, and hydrogen bonds occur between the bound O(2) and the amide nitrogen
of Gly-139 and a distal pocket water molecule, which is a part of an extended
hydrogen bonding network that provides the solvent protons required for oxygen
activation. In addition, the O-O bond is orthogonal to the plane of the proximal
imidazole side chain, which facilitates hydroxylation of the porphyrin
alpha-meso-carbon by preventing premature O-O bond cleavage.
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Figure 1.
FIG. 1. Schematics of heme oxygenase catalytic
intermediates.
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Figure 3.
FIG. 3. Structure of the oxygen binding site. The final
 [A]-weighted 2F[o] -
F[c] map (blue) at the 1.8 level and the simulated
annealing omit F[o] - F[c] map (red) at the 4.2 level.
Water molecules are represented by W plus a number, and D, G,
and Q are standard single letter amino acid abbreviations with
position numbers.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
21055-21061)
copyright 2004.
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