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PDBsum entry 4d4x
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Electron transport
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PDB id
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4d4x
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References listed in PDB file
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Key reference
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Title
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Hydrogen bonding of the dissociated histidine ligand is not required for formation of a proximal no adduct in cytochrome c'.
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Authors
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D.D.Ghafoor,
D.Kekilli,
G.H.Abdullah,
F.S.Dworkowski,
H.G.Hassan,
M.T.Wilson,
R.W.Strange,
M.A.Hough.
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Ref.
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J Biol Inorg Chem, 2015,
20,
949-956.
[DOI no: ]
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PubMed id
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Abstract
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Cytochromes c', that occur in methanotrophic, denitrifying and photosynthetic
bacteria, form unusual proximal penta-coordinate NO complexes via a
hexa-coordinate distal NO intermediate. Their NO binding properties are similar
to those of the eukaryotic NO sensor, soluble guanylate cyclase, for which they
provide a valuable structural model. Previous studies suggested that hydrogen
bonding between the displaced proximal histidine (His120) ligand (following its
dissociation from heme due to trans effects from the distally bound NO) and a
conserved aspartate residue (Asp121) could play a key role in allowing proximal
NO binding to occur. We have characterized three variants of Alcaligenes
xylosoxidans cytochrome c' (AXCP) where Asp121 has been replaced by Ala, Ile and
Gln, respectively. In all variants, hydrogen bonding between residue 121 and
His120 is abolished yet 5-coordinate proximal NO species are still formed. Our
data therefore demonstrate that the His120-Asp121 bond is not essential for
proximal NO binding although it likely provides an energy minimum for the
displaced His ligand. All variants have altered proximal pocket structure
relative to native AXCP.
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