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PDBsum entry 5cib
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Electron transport/oxidoreductase
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PDB id
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5cib
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References listed in PDB file
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Key reference
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Title
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Constraints on the radical cation center of cytochrome c peroxidase for electron transfer from cytochrome c.
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Authors
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T.M.Payne,
E.F.Yee,
B.Dzikovski,
B.R.Crane.
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Ref.
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Biochemistry, 2016,
55,
4807-4822.
[DOI no: ]
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PubMed id
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Note: In the PDB file this reference is
annotated as "TO BE PUBLISHED". The citation details given above have
been manually determined.
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Abstract
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The tryptophan 191 cation radical of cytochrome c peroxidase (CcP) compound I
(Cpd I) mediates long-range electron transfer (ET) to cytochrome c (Cc). Here we
test the effects of chemical substitution at position 191. CcP W191Y forms a
stable tyrosyl radical upon reaction with peroxide and produces spectral
properties similar to those of Cpd I but has low reactivity toward reduced Cc.
CcP W191G and W191F variants also have low activity, as do redox ligands that
bind within the W191G cavity. Crystal structures of complexes between Cc and CcP
W191X (X = Y, F, or G), as well as W191G with four bound ligands reveal similar
1:1 association modes and heme pocket conformations. The ligands display
structural disorder in the pocket and do not hydrogen bond to Asp235, as does
Trp191. Well-ordered Tyr191 directs its hydroxyl group toward the porphyrin
ring, with no basic residue in the range of interaction. CcP W191X (X = Y, F, or
G) variants substituted with zinc-porphyrin (ZnP) undergo photoinduced ET with
Cc(III). Their slow charge recombination kinetics that result from loss of the
radical center allow resolution of difference spectra for the charge-separated
state [ZnP(+), Cc(II)]. The change from a phenyl moiety at position 191 in W191F
to a water-filled cavity in W191G produces effects on ET rates much weaker than
the effects of the change from Trp to Phe. Low net reactivity of W191Y toward
Cc(II) derives either from the inability of ZnP(+) or the Fe-CcP ferryl to
oxidize Tyr or from the low potential of the resulting neutral Tyr radical.
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