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PDBsum entry 2e7e
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Oxidoreductase
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PDB id
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2e7e
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References listed in PDB file
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Key reference
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Title
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Alternative cyanide-Binding modes to the haem iron in haem oxygenase.
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Authors
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M.Sugishima,
K.Oda,
T.Ogura,
H.Sakamoto,
M.Noguchi,
K.Fukuyama.
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Ref.
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Acta Crystallogr Sect F Struct Biol Cryst Commun, 2007,
63,
471-474.
[DOI no: ]
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PubMed id
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Abstract
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Cyanide is a well known potent inhibitor of haem proteins, including haem
oxygenase (HO). Generally, cyanide coordinates to the ferric haem iron with a
linear binding geometry; the Fe-C-N angle ranges from 160 to 180 degrees . The
Fe-C-N angle observed in the crystal structure of haem-HO bound to cyanide
prepared at alkaline pH was 166 degrees . Here, it is reported that cyanide can
bind to the haem iron in HO in a bent mode when the ternary complex is prepared
at neutral pH; a crystal structure showed that the Fe-C-N angle was bent by 47
degrees . Unlike the ternary complex prepared at alkaline pH, in which the haem
group, including the proximal ligand and the distal helix, was displaced upon
cyanide binding, the positions of the haem group and the distal helix in the
complex prepared at neutral pH were nearly identical to those in haem-HO.
Cyanide that was bound to haem-HO with a bent geometry was readily
photodissociated, whereas that bound with a linear geometry was not
photodissociated. Thus, alternative cyanide-binding modes with linear and bent
geometries exist in the crystalline state of haem-HO.
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Figure 2.
Superimposition of haem --HO (green; Sugishima et al.,
2003[triangle]), CN^[minus sign] --haem --HO (yellow, pH 6.8)
and CN^[minus sign] --haem --HO (blue, pH 9.7). Except for the
proximal histidine, only the C^[alpha] traces are shown for
clarity. The crystal structures of CN^[minus sign] --haem --HO
at pH 6.8 and pH 9.7 were superimposed on the structure of haem
--HO so as to minimize the r.m.s. deviations of C^[alpha] atoms.
Following the distal helix is the G-helix, which contains the
basic residues (Lys179 and Arg183) involved in the salt bridges
to haem propionates. Acta Crystallogr Sect F Struct Biol Cryst
Commun. 2007 June 1; 63(Pt 6): 471–474. Published online 2007
May 31. doi: 10.1107/S174430910702475X. Copyright [copyright]
International Union of Crystallography 2007
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Figure 3.
Photodissociation of cyanide. A difference Fourier map
calculated between data sets obtained in the dark and under
continuous illumination from a red laser is superimposed on the
ball-and-stick model around the haem group. Blue and red
indicate newly appeared and the diminished densities,
respectively (contoured at [plus minus]3[sigma]). (a) 5 mM KCN
pH 6.8. (b) 50 mM KCN pH 9.7. Acta Crystallogr Sect F Struct
Biol Cryst Commun. 2007 June 1; 63(Pt 6): 471–474. Published
online 2007 May 31. doi: 10.1107/S174430910702475X. Copyright
[copyright] International Union of Crystallography 2007
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The above figures are
reprinted
from an Open Access publication published by the IUCr:
Acta Crystallogr Sect F Struct Biol Cryst Commun
(2007,
63,
471-474)
copyright 2007.
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