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Thermal unfolding of staphylococcal nuclease and several mutant forms thereof studied by differential scanning calorimetry
Author(s) -
Tanaka Akiyoshi,
Sturtevant Julian M.,
Flanagan John
Publication year - 1993
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560020408
Subject(s) - differential scanning calorimetry , chemistry , calorimetry , crystallography , thermodynamics , nuclease , protein folding , atmospheric temperature range , biochemistry , physics , enzyme
Abstract The effects of eight mutations on the thermodynamics of the reversible thermal unfolding of staphylococcal nuclease have been determined over a range of pH and protein concentration by means of differential scanning calorimetry. Variation of the protein concentration was included in our study because we found a significant dependence of the thermodynamics of protein unfolding on concentration. Values for the change in the standard free energy of unfolding, ΔΔ G d 0 , produced by the mutations in the pH range 5.0–7.0 varied from 1.9 kcal mol −1 (apparent stabilization) for H124L to ‐2.8 kcal mol −1 (apparent destabilization) for L25A. As has been observed in numerous other cases, there is no correlation in magnitude or sign between ΔΔ G d 0 and the corresponding values for ΔΔ H d and T ΔΔ S d 0 , the latter quantities being in most cases much larger in magnitude than ΔΔ G d 0 . This fact emphasizes the difficulty in attempting to correlate the thermodynamic changes with structural changes observed by X‐ray crystallography.