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PDBsum entry 2evk
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Oxygen storage/transport
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PDB id
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2evk
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References listed in PDB file
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Key reference
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Title
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Structures of thiolate- And carboxylate-Ligated ferric h93g myoglobin: models for cytochrome p450 and for oxyanion-Bound heme proteins.
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Authors
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J.Qin,
R.Perera,
L.L.Lovelace,
J.H.Dawson,
L.Lebioda.
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Ref.
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Biochemistry, 2006,
45,
3170-3177.
[DOI no: ]
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PubMed id
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Abstract
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Crystal structures of the ferric H93G myoglobin (Mb) cavity mutant containing
either an anionic proximal thiolate sulfur donor or a carboxylate oxygen donor
ligand are reported at 1.7 and 1.4 A resolution, respectively. The crystal
structure and magnetic circular dichroism spectra of the H93G Mb
beta-mercaptoethanol (BME) thiolate adduct reveal a high-spin, five-coordinate
complex. Furthermore, the bound BME appears to have an intramolecular hydrogen
bond involving the alcohol proton and the ligated thiolate sulfur, mimicking one
of the three proximal N-H...S hydrogen bonds in cytochrome P450. The Fe is
displaced from the porphyrin plane by 0.5 A and forms a 2.41 A Fe-S bond. The
Fe(3+)-S-C angle is 111 degrees , indicative of a covalent Fe-S bond with
sp(3)-hybridized sulfur. Therefore, the H93G Mb.BME complex provides an
excellent protein-derived structural model for high-spin ferric P450. In
particular, the Fe-S bond in high-spin ferric P450-CAM has essentially the same
geometry despite the constraints imposed by covalent linkage of the cysteine to
the protein backbone. This suggests that evolution led to the geometric
optimization of the proximal Fe-S(cysteinate) bond in P450. The crystal
structure and spectral properties of the H93G Mb acetate adduct reveal a
high-spin, six-coordinate complex with proximal acetate and distal water axial
ligands. The distal His-64 forms a hydrogen bond with the bound water. The
Fe-acetate bonding geometry is inconsistent with an electron pair along the Fe-O
bond as the Fe-O-C angle is 152 degrees and the Fe is far from the plane of the
acetate. Thus, the Fe-O bonding is ionic. The H93G Mb cavity mutant has already
been shown to be a versatile model system for the study of ligand binding to
heme proteins; this investigation affords the first structural evidence that
nonimidazole exogenous ligands bind in the proximal ligation site.
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