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PDBsum entry 1pm2
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Oxidoreductase
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PDB id
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1pm2
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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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Variable coordination geometries at the diiron(ii) active site of ribonucleotide reductase r2.
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Authors
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W.C.Voegtli,
M.Sommerhalter,
L.Saleh,
J.Baldwin,
J.M.Bollinger,
A.C.Rosenzweig.
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Ref.
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J Am Chem Soc, 2003,
125,
15822-15830.
[DOI no: ]
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PubMed id
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Abstract
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The R2 subunit of Escherichia coli ribonucleotide reductase contains a dinuclear
iron center that generates a catalytically essential stable tyrosyl radical by
one electron oxidation of a nearby tyrosine residue. After acquisition of Fe(II)
ions by the apo protein, the resulting diiron(II) center reacts with O(2) to
initiate formation of the radical. Knowledge of the structure of the reactant
diiron(II) form of R2 is a prerequisite for a detailed understanding of the O(2)
activation mechanism. Whereas kinetic and spectroscopic studies of the reaction
have generally been conducted at pH 7.6 with reactant produced by the addition
of Fe(II) ions to the apo protein, the available crystal structures of diferrous
R2 have been obtained by chemical or photoreduction of the oxidized diiron(III)
protein at pH 5-6. To address this discrepancy, we have generated the diiron(II)
states of wildtype R2 (R2-wt), R2-D84E, and R2-D84E/W48F by infusion of Fe(II)
ions into crystals of the apo proteins at neutral pH. The structures of
diferrous R2-wt and R2-D48E determined from these crystals reveal diiron(II)
centers with active site geometries that differ significantly from those
observed in either chemically or photoreduced crystals. Structures of R2-wt and
R2-D48E/W48F determined at both neutral and low pH are very similar, suggesting
that the differences are not due solely to pH effects. The structures of these
"ferrous soaked" forms are more consistent with circular dichroism (CD) and
magnetic circular dichroism (MCD) spectroscopic data and provide alternate
starting points for consideration of possible O(2) activation mechanisms.
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