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PDBsum entry 1v07
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Oxygen transport
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PDB id
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1v07
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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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Thr-E11 regulates o2 affinity in cerebratulus lacteus mini-Hemoglobin.
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Authors
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A.Pesce,
M.Nardini,
P.Ascenzi,
E.Geuens,
S.Dewilde,
L.Moens,
M.Bolognesi,
A.F.Riggs,
A.Hale,
P.Deng,
G.U.Nienhaus,
J.S.Olson,
K.Nienhaus.
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Ref.
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J Biol Chem, 2004,
279,
33662-33672.
[DOI no: ]
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PubMed id
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Abstract
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The mini-hemoglobin from Cerebratulus lacteus (CerHb) belongs to a class of
globins containing the polar Tyr-B10/Gln-E7 amino acid pair that normally causes
low rates of O2 dissociation and ultra-high O2 affinity, which suggest O2
sensing or NO scavenging functions. CerHb, however, has high rates of O2
dissociation (kO2 = 200-600 s(-1)) and moderate O2 affinity (KO2) approximately
1 microm(-1)) as a result of a third polar amino acid in its active site,
Thr-E11. When Thr-E11 is replaced by Val, kO2 decreases 1000-fold and KO2
increases 130-fold at pH 7.0, 20 degrees C. The mutation also shifts the
stretching frequencies of both heme-bound and photodissociated CO, indicating
marked changes of the electrostatic field at the active site. The crystal
structure of Thr-E11 --> Val CerHbO2 at 1.70 A resolution is almost identical to
that of the wild-type protein (root mean square deviation of 0.12 A). The
dramatic functional and spectral effects of the Thr-E11 --> Val mutation are due
exclusively to changes in the hydrogen bonding network in the active site.
Replacing Thr-E11 with Val "frees" the Tyr-B10 hydroxyl group to
rotate toward and donate a strong hydrogen bond to the heme-bound ligand,
causing a selective increase in O2 affinity, a decrease of the rate coefficient
for O2 dissociation, a 40 cm(-1) decrease in nuCO of heme-bound CO, and an
increase in ligand migration toward more remote intermediate sites.
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Figure 1.
FIG. 1. a, O[2] rebinding to wild-type CerHb, Thr-E11  Val
CerHb, and wild-type sperm whale (sw) Mb at pH 7.0, 20 °C.
The concentration of O[2] was 1,250 µM (buffer
equilibrated with 1 atm pure O[2]). O[2] displacement from
wild-type CerHbO[2], Thr-E11 Val CerHbO[2], and
wild-type sperm whale MbO[2] at pH 7.0, 20 °C is shown on
short (b) and long (c) time scales.
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Figure 2.
FIG. 2. A stereo view of the CerHb heme distal (upper part
of the figure) and proximal sites (lower part, hosting His-F8).
Short fragments of the B- and E-helices are displayed as cyan
ribbons. The heme is shown in red. The relevant residues are
displayed with light gray bonds, using black labels for the
wild-type CerHb structure. Structural modifications observed in
the Thr-E11 Val CerHb mutant are
highlighted by displaying residues Tyr-B10 and Val E11
in orange. The dashed arrows indicate hydrogen bond donation in
the wild-type protein (blue arrows) and in the Thr-E11 Val
mutant (orange arrow). The O[2] molecule is displayed at the
sixth coordination site of the heme iron as a purple diatomic
species (partly covered by arrows). Lys-E10 is electrostatically
coupled to both heme propionates and contributes to the
shielding of the distal heme pocket.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
33662-33672)
copyright 2004.
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