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Title
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Contribution of the hydrophobic effect to the stability of human lysozyme: calorimetric studies and X-ray structural analyses of the nine valine to alanine mutants.
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Authors
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K.Takano,
Y.Yamagata,
S.Fujii,
K.Yutani.
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Ref.
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Biochemistry, 1997,
36,
688-698.
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PubMed id
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Abstract
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To clarify the contribution of the hydrophobic effect to the conformational
stability of human lysozyme, a series of Val to Ala mutants were constructed.
The thermodynamic parameters for the denaturation of these nine mutant proteins
were determined using differential scanning calorimetry (DSC), and the crystal
structures were solved at high resolution. The denaturation Gibbs energy (delta
delta G) and enthalpy (delta delta H) values of the mutant proteins ranged from
+2.2 to- 6.3 kJ/mol and from +7 to -17 kJ/mol, respectively. The structural
analyses showed that the mutation site and/or the residues around it in some
proteins shifted toward the created cavity, and the substitutions affected not
only the mutations site but also other parts far from the site, although the
structural changes were not as great. Correlation between the changes in the
thermodynamic parameters and the structural features of mutant proteins was
examined, including the five Ile to Val mutant human lysozymes [Takano et al.
(1995) J. Mol. Biol. 254, 62-76]. There was no simple general correlation
between delta delta G and the changes in hydrophobic surface area exposed upon
denaturation (delta delta ASAHP). We found only a new correlation between the
delta delta G and delta delta ASAHP of all of the hydrophobic residues if the
effect of the secondary structure propensity was taken into account.
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