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PDBsum entry 2hz3
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Oxygen storage/transport
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PDB id
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2hz3
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References listed in PDB file
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Key reference
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Title
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Covalent heme attachment in synechocystis hemoglobin is required to prevent ferrous heme dissociation.
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Authors
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J.A.Hoy,
B.J.Smagghe,
P.Halder,
M.S.Hargrove.
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Ref.
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Protein Sci, 2007,
16,
250-260.
[DOI no: ]
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PubMed id
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Abstract
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Synechocystis hemoglobin contains an unprecedented covalent bond between a
nonaxial histidine side chain (H117) and the heme 2-vinyl. This bond has been
previously shown to stabilize the ferric protein against denaturation, and also
to affect the kinetics of cyanide association. However, it is unclear why
Synechocystis hemoglobin would require the additional degree of stabilization
accompanying the His117-heme 2-vinyl bond because it also displays endogenous
bis-histidyl axial heme coordination, which should greatly assist heme
retention. Furthermore, the mechanism by which the His117-heme 2-vinyl bond
affects ligand binding has not been reported, nor has any investigation of the
role of this bond on the structure and function of the protein in the ferrous
oxidation state. Here we report an investigation of the role of the
Synechocystis hemoglobin His117-heme 2-vinyl bond on structure, heme
coordination, exogenous ligand binding, and stability in both the ferrous and
ferric oxidation states. Our results reveal that hexacoordinate Synechocystis
hemoglobin lacking this bond is less stable in the ferrous oxidation state than
the ferric, which is surprising in light of our understanding of pentacoordinate
Hb stability, in which the ferric protein is always less stable. It is also
demonstrated that removal of the His117-heme 2-vinyl bond increases the affinity
constant for intramolecular histidine coordination in the ferric oxidation
state, thus presenting greater competition for the ligand binding site and
lowering the observed rate and affinity constants for exogenous ligands.
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Figure 1.
Figure 1. SynHb (gray) versus SynH117A (colored by RMSD from SynHb,
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Figure 2.
Figure 2. Rapid mixing kinetic measurement of CO binding. (A) Change
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The above figures are
reprinted
by permission from the Protein Society:
Protein Sci
(2007,
16,
250-260)
copyright 2007.
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