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Title
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High-resolution crystal structure of magnesium (MgII)-iron (FeII) hybrid hemoglobin with liganded beta subunits.
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Authors
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S.Y.Park,
A.Nakagawa,
H.Morimoto.
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Ref.
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J Mol Biol, 1996,
255,
726-734.
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PubMed id
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Abstract
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The structures of deoxy (alpha(Mg(II))2 beta(Fe(II))2) and CO-liganded
(alpha(Mg(II)2(Fe(II)-CO)2) forms of human hemoglobin were determined by X-ray
crystallography to a resolution of 1.7 A and 1.9 A, respectively. The deoxy
hybrid has virtually the same structure as that of the native deoxy HbA. Both
the deoxy and CO-liganded hybrids assumed a T quaternary structure
characteristic of native deoxy HbA. No significant structural difference was
found between the alpha subunits of the CO-liganded hybrid and deoxy HbA, while
in the beta subunit, significant tertiary structural changes were confined to
the heme pocket. Baldwin showed by a comparison of COHbA and deoxy HbA that
there is a 1.5 A shift of the beta subunit heme into its pocket. This shift was
much reduced in alpha(Mg(II))2 beta(Fe(II)-CO)2. On the other hand, when the two
structures are compared with superposition of hemes, the nearest neighbors of CO
(Fe, E11 Val and E7 His) have shifted nearly to the same positions as those in
COHbA. Thus the tertiary structure of the beta subunit of alpha(Mg(II))2
beta(Fe(II)-CO)2 is such that the CO molecule and the neighboring atoms assume
nearly the same conformation as those of COHbA, while the block shift of these
groups is impeded with respect to the structural invariant portions of the
molecule.
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