Thermal unfolding of staphylococcal nuclease and several mutant forms thereof studied by differential scanning calorimetry

✍ Scribed by Akiyoshi Tanaka; Julian M. Sturtevant; John Flanagan

• Book ID: 105356119
• Publisher: Cold Spring Harbor Laboratory Press
• Year: 2008
• Tongue: English
• Weight: 829 KB
• Volume: 2
• Category: Article
• ISSN: 0961-8368
• DOI: 10.1002/pro.5560020408

✦ Synopsis

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.