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PDBsum entry 1v4u
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Oxygen storage/transport
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PDB id
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1v4u
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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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Novel mechanisms of ph sensitivity in tuna hemoglobin: a structural explanation of the root effect.
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Authors
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T.Yokoyama,
K.T.Chong,
G.Miyazaki,
H.Morimoto,
D.T.Shih,
S.Unzai,
J.R.Tame,
S.Y.Park.
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Ref.
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J Biol Chem, 2004,
279,
28632-28640.
[DOI no: ]
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PubMed id
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Abstract
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The crystal structure of hemoglobin has been known for several decades, yet
various features of the molecule remain unexplained or controversial. Several
animal hemoglobins have properties that cannot be readily explained in terms of
their amino acid sequence and known atomic models of hemoglobin. Among these,
fish hemoglobins are well known for their widely varying interactions with
heterotropic effector molecules and pH sensitivity. Some fish hemoglobins are
almost completely insensitive to pH (within physiological limits), whereas
others show extremely low oxygen affinity under acid conditions, a phenomenon
called the Root effect. X-ray crystal structures of Root effect hemoglobins have
not, to date, provided convincing explanations of this effect. Sequence
alignments have signally failed to pinpoint the residues involved, and
site-directed mutagenesis has not yielded a human hemoglobin variant with this
property. We have solved the crystal structure of tuna hemoglobin in the deoxy
form at low and moderate pH and in the presence of carbon monoxide at high pH. A
comparison of these models shows clear evidence for novel mechanisms of
pH-dependent control of ligand affinity.
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Figure 3.
FIG. 3. Stereo overlay of the  heme pocket of tuna Hb
and HbA. The deoxy form (pH 7.5) (a) and the CO form (b) are
shown. HbA is shown in blue, and the residue numbers of the
human protein are shown in brackets. The atoms and bonds of tuna
Hb are colored by atom type as follows: yellow, carbon; red,
oxygen; blue, nitrogen.
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Figure 7.
FIG. 7. The C-terminal histidine of the  chains in the deoxy
form. The position of this residue is almost identical in the
structures at pH 5 and 7.5. Ser-93 hydrogen bonds to Asp-94
through its side chain
hydroxyl group (shown as a red dotted line), but the imidazole
group of His-146 is too far (>3.5
Å) from the Asp for a strong bonding interaction.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
28632-28640)
copyright 2004.
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