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PDBsum entry 1oaf
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Oxidoreductase
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PDB id
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1oaf
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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 ascorbate peroxidase-Ascorbate complex.
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Authors
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K.H.Sharp,
M.Mewies,
P.C.Moody,
E.L.Raven.
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Ref.
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Nat Struct Biol, 2003,
10,
303-307.
[DOI no: ]
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PubMed id
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Abstract
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Heme peroxidases catalyze the H2O2-dependent oxidation of a variety of
substrates, most of which are organic. Mechanistically, these enzymes are well
characterized: they share a common catalytic cycle that involves formation of a
two-electron, oxidized Compound I intermediate followed by two single-electron
reduction steps by substrate. The substrate specificity is more diverse--most
peroxidases oxidize small organic substrates, but there are prominent
exceptions--and there is a notable absence of structural information for a
representative peroxidase-substrate complex. Thus, the features that control
substrate specificity remain undefined. We present the structure of the complex
of ascorbate peroxidase-ascorbate. The structure defines the ascorbate-binding
interaction for the first time and provides new rationalization of the unusual
functional features of the related cytochrome c peroxidase enzyme, which has
been a benchmark for peroxidase catalysis for more than 20 years. A new
mechanism for electron transfer is proposed that challenges existing views of
substrate oxidation in other peroxidases.
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Figure 1.
Figure 1. The active site of rsAPX32, 33. The key residues
are labeled, and water molecules are shown as red spheres.
Hydrogen bonds are indicated by green dotted lines.
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Figure 2.
Figure 2. The ascorbate-binding site. a, Stereo
representation of the overall structure of the rsAPX -ascorbate
complex34, showing the heme, the proximal and distal histidine
residues, the coordinated water molecule and the bound
ascorbate. The regions 20 -35 and 179 -181 (shown in Fig. 3) are
highlighted in magenta. b, The structure of L-ascorbic acid,
showing the L configuration at C^5. The pK[a]s of the 2-OH and
3-OH groups are 11.3 and 4.0, respectively35. c, The structure
of rsAPX showing the  -meso
and  -meso
positions of the heme and bound solvent in the ascorbate-binding
site. d, Stereo view of the rsAPX -ascorbate complex, showing
refined electron density (green) and the binding of the
ascorbate. Hydrogen bonds are indicated (dotted lines)32, 33.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nat Struct Biol
(2003,
10,
303-307)
copyright 2003.
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