Entropic stabilization of a mutant human lysozyme induced by calcium binding

  • Kuroki R
  • Kawakita S
  • Nakamura H
 et al. 
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The stabilization mechanism of the mutant human lysozyme with a calcium
binding site (D86/92) was investigated by using calorimetric approaches.
By differential scanning calorimetry, the enthalpy change (delta
H) in the unfolding of holo-D86/92 was found to be 6.8 kcal/mol smaller
than that of the wild-type and apo-D86/92 lysozymes at 85 degrees
C. However, the unfolding Gibbs energy change (delta G) of the holo
mutant was 3.3 kcal/mol greater than the apo type at 85 degrees C,
indicating a significant decrease of entropy (T delta S = 10.1 kcal/mol)
in the presence of Ca2+. Subsequently, the Ca2+ binding process in
the folded state of the mutant was analyzed by using titration isothermal
calorimetry. The binding enthalpy change was estimated to be 4.5
kcal/mol, and delta G was -8.1 kcal/mol at 85 degrees C, which indicates
that the binding was caused by a large increase in entropy (T delta
S = 12.6 kcal/mol). From these analyses, the unfolded holo mutant
was determined to bind Ca2+ with a binding delta G of -4.8 kcal/mol
(delta H = -2.6 kcal/mol, T delta S = 2.2 kcal/mol) at 85 degrees
C. Therefore, the major cause of stabilization of holo-D86/92 is
the decrease in entropy of the peptide chain due to Ca2+ binding
to the unfolded protein.

Author-supplied keywords

  • Amino Acid Sequence Binding Sites Calcium/*metabol
  • Differential Scanning Enzyme Stability Human Kine
  • Non-U.S. Gov't
  • Site-Directed Protein Conformation Protein Denatu

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  • PMID: 1495968


  • R Kuroki

  • S Kawakita

  • H Nakamura

  • K Yutani

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