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PDBsum entry 2a1m
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Oxidoreductase
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PDB id
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2a1m
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References listed in PDB file
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Key reference
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Title
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Crystallographic study on the dioxygen complex of wild-Type and mutant cytochrome p450cam. Implications for the dioxygen activation mechanism.
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Authors
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S.Nagano,
T.L.Poulos.
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Ref.
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J Biol Chem, 2005,
280,
31659-31663.
[DOI no: ]
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PubMed id
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Abstract
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Two key amino acids, Thr252 and Asp251, are known to be important for dioxygen
activation by cytochrome P450cam. We have solved crystal structures of a
critical intermediate, the ferrous dioxygen complex (Fe(II)-O2), of the
wild-type P450cam and its mutants, D251N and T252A. The wild-type dioxygen
complex structure is very much the same as reported previously (Schlichting, I.,
Berendzen, J., Chu, K., Stock, A. M., Maves, S. A., Benson, D. E., Sweet, R. M.,
Ringe, D., Petsko, G. A., and Sligar, S. G. (2000) Science 287, 1615-1622) with
the exception of higher occupancy and a more ordered structure of the
iron-linked dioxygen and two "catalytic" water molecules that form
part of a proton relay system to the iron-linked dioxygen. Due to of the altered
conformation of the I helix groove these two waters are missing in the D251N
dioxygen complex which explains its lower catalytic activity and slower proton
transfer to the dioxygen ligand. Similarly, the T252A mutation was expected to
disrupt the active site solvent structure leading to hydrogen peroxide formation
rather than substrate hydroxylation. Unexpectedly, however, the two
"catalytic" waters are retained in the T252A mutant. Based on these
findings, we propose that the Thr(252) accepts a hydrogen bond from the
hydroperoxy (Fe(III)-OOH) intermediate that promotes the second protonation on
the distal oxygen atom, leading to O-O bond cleavage and compound I formation.
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Figure 1.
FIG. 1. A, the structure of P450cam highlighting the I
helix and the catalytically important residues, Thr252 and
Asp251. B, the P450 oxygen activation mechanism. Electron and
proton transfer to the ferrous dioxygen complex gives the
Fe(III)-OOH hydroperoxy intermediate. A second protonation of
the distal oxygen atom leads to heterolysis of the dioxygen O-O
bond and formation of Fe(IV)=O, the active hydroxylating species.
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Figure 4.
FIG. 4. Possible hydrogen bond network for the P450cam
hydroperoxy intermediate. The distances between heteroatoms are
taken from molecule B of our WT dioxygen complex structure.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2005,
280,
31659-31663)
copyright 2005.
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Secondary reference #1
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Title
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Crystal structures of the ferrous dioxygen complex of wild-Type cytochrome p450eryf and its mutants, A245s and a245t: investigation of the proton transfer system in p450eryf.
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Authors
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S.Nagano,
J.R.Cupp-Vickery,
T.L.Poulos.
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Ref.
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J Biol Chem, 2005,
280,
22102-22107.
[DOI no: ]
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PubMed id
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Figure 1.
FIG. 1. Active site structure and electron density maps of
the WT O ·P450eryF. Active site residues, substrate, and
heme are shown as a stick model (green, carbon; blue, nitrogen;
red, oxygen; orange, sulfur; purple 2, iron). Water molecules 53
and 63 are shown as red spheres. Yellow broken lines show the
presumed proton transfer pathway. The substrate C-5 and C-6
atoms are labeled. The simulated-annealing omit maps of F[o] -
F[c] contoured at 5  (A) and of the 2F[o] -
F[c] contoured at 1.5 (B). The dioxygen
ligand and waters 53 and 63 are omitted from the map calculation.
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Figure 3.
FIG. 3. Superimposed structures of O[2]·P450eryF and
O[2]-P450cam. The red and green stick models show the
O[2]-P450cam (Protein Data Bank code 1DZ8 [PDB]
(15)) and O[2]·P450eryF, respectively.
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The above figures are
reproduced from the cited reference
with permission from the ASBMB
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