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PDBsum entry 1wzf
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Oxidoreductase
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PDB id
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1wzf
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References listed in PDB file
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Key reference
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Title
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Design of metal cofactors activated by a protein-Protein electron transfer system.
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Authors
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T.Ueno,
N.Yokoi,
M.Unno,
T.Matsui,
Y.Tokita,
M.Yamada,
M.Ikeda-Saito,
H.Nakajima,
Y.Watanabe.
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Ref.
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Proc Natl Acad Sci U S A, 2006,
103,
9416-9421.
[DOI no: ]
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PubMed id
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Abstract
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Protein-to-protein electron transfer (ET) is a critical process in biological
chemistry for which fundamental understanding is expected to provide a wealth of
applications in biotechnology. Investigations of protein-protein ET systems in
reductive activation of artificial cofactors introduced into proteins remains
particularly challenging because of the complexity of interactions between the
cofactor and the system contributing to ET. In this work, we construct an
artificial protein-protein ET system, using heme oxygenase (HO), which is known
to catalyze the conversion of heme to biliverdin. HO uses electrons provided
from NADPH/cytochrome P450 reductase (CPR) through protein-protein complex
formation during the enzymatic reaction. We report that a Fe(III)(Schiff-base),
in the place of the active-site heme prosthetic group of HO, can be reduced by
NADPH/CPR. The crystal structure of the Fe(10-CH(2)CH(2)COOH-Schiff-base).HO
composite indicates the presence of a hydrogen bond between the propionic acid
carboxyl group and Arg-177 of HO. Furthermore, the ET rate from NADPH/CPR to the
composite is 3.5-fold faster than that of Fe(Schiff-base).HO, although the redox
potential of Fe(10-CH(2)CH(2)COOH-Schiff-base).HO (-79 mV vs. NHE) is lower than
that of Fe(Schiff-base).HO (+15 mV vs. NHE), where NHE is normal hydrogen
electrode. This work describes a synthetic metal complex activated by means of a
protein-protein ET system, which has not previously been reported. Moreover, the
result suggests the importance of the hydrogen bond for the ET reaction of HO.
Our Fe(Schiff-base).HO composite model system may provide insights with regard
to design of ET biosystems for sensors, catalysts, and electronics devices.
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Figure 1.
Fig. 1. Catalytic reaction of HO. (A) Enzymatic cycle of
heme metabolism to biliverdin catalyzed by HO. The reactions
shaded in blue indicate the ET step from CPR to heme to be used
for the reduction of Fe^III(Schiff-base) complexes. (B) Chemical
structures of heme (Left) and Fe^III(Schiff-base) (Right).
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Figure 2.
Fig. 2. Close-up views of coordination geometries of the
metal cofactors in the HO active-site region. Refined model
coordinates for the active site region are superimposed on 2F[o]
– F[c] maps contoured at 1.0  , except for
heme·HO, with elements of the protein and cofactors in
ball-and-stick models for top (Left) and side (Right) views.
Green is carbon, and purple, red, and pink are nitrogen, oxygen,
and iron, respectively. (A) Heme·HO. (B) 1·HO
refined to 1.35 Å. (C) 2·HO refined to 1.85
Å. (D) 3·HO refined to 1.75 Å.
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