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Title
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Mutation of tyrosine-67 to phenylalanine in cytochrome c significantly alters the local heme environment.
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Authors
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A.M.Berghuis,
J.G.Guillemette,
M.Smith,
G.D.Brayer.
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Ref.
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J Mol Biol, 1994,
235,
1326-1341.
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PubMed id
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Abstract
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The high resolution three-dimensional atomic structures of the reduced and
oxidized states of the Y67F variant of yeast iso-1-cytochrome c have been
completed. The conformational differences observed are localized directly in the
mutation site and in the region about the pyrrole A propionate. Shifts in atomic
positions are largely restricted to nearby amino acid side-chains, whereas
little perturbation of the polypeptide chain backbone is observed. One prominent
difference between the variant and wild-type structures involves a substantial
increase in the size of an already existing internal cavity adjacent to residue
67. This same cavity contains an internally bound water molecule (Wat166), which
is found in all eukaryotic cytochromes c for which structures are available. In
the reduced Y67F mutant protein a second water molecule (Wat300) is observed to
reside in this enlarged internal cavity, assuming a position approximately
equivalent to that of the hydroxyl group of Tyr67 in the wild-type protein. A
further consequence of this mutation is the alteration of the hydrogen bond
network between Tyr67, Wat166 and other nearby residues. This appears to be
responsible for the absence of oxidation state dependent changes in polypeptide
chain flexibility observed in the wild-type protein. Furthermore, loss of the
normally resident Tyr67 OH to Met80 SD hydrogen bond leads to a significantly
lower midpoint reduction potential. These results reaffirm proposals that both
Tyr67 and Wat166 play a central role in stabilizing the alternative oxidation
states of cytochrome c.
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