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Title
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Contribution of hydrophobic residues to the stability of human lysozyme: calorimetric studies and X-ray structural analysis of the five isoleucine to valine mutants.
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Authors
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K.Takano,
K.Ogasahara,
H.Kaneda,
Y.Yamagata,
S.Fujii,
E.Kanaya,
M.Kikuchi,
M.Oobatake,
K.Yutani.
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Ref.
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J Mol Biol, 1995,
254,
62-76.
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PubMed id
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Abstract
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In order to understand the contribution of hydrophobic residues to the
conformational stability of human lysozyme, five Ile mutants (Ile --> Val) in
the interior of the protein were constructed. The thermodynamic parameters
characterizing the denaturation of these mutant proteins were determined by
scanning calorimetry, and the three-dimensional structure of each mutant protein
was solved at high resolution by X-ray crystallography. The thermodynamic
analyses at 64.9 degrees C and at pH 2.7 revealed the following. (1) The
stabilities of all the mutant proteins were decreased as compared with that of
the wild-type protein. (2) The changes in the calorimetric enthalpies were
larger than those in the Gibbs energies, and were compensated by entropy
changes. (3) The destabilization mechanism of the mutant proteins differs,
depending on the location of the mutation sites. X-ray analyses showed that the
overall structures of all the mutant human lysozymes examined were identical to
that of the wild-type protein, and only small structural rearrangements were
observed locally around some of the mutation sites. The most striking change
among the mutant proteins was found in the mutant protein, 159V, which contains
a new water molecule in the cavity created by the mutation. The thermodynamic
stabilities of the mutant proteins are discussed in light of the high-resolution
X-ray structures of the wild-type and five mutant human lysozymes examined.
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