Research article

The effects of NaCl concentration and pH on the stability of hyperthermophilic protein Ssh10b

Yong-Jin Mao^1,3 , Xiang-Rong Sheng² and Xian-Ming Pan^1,2

¹  National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China

²  Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, 100084, China

³  Graduate University of Chinese Academy of Sciences, Beijing, 100049, China

author email corresponding author email

BMC Biochemistry 2007, 8:28doi:10.1186/1471-2091-8-28

Published:	21 December 2007

Abstract

Background

Hyperthermophiles constitute a group of microorganisms with an optimum growth temperature of between 80°C and 100°C. Although the molecular underpinnings of protein thermostabilization have been the focus of many theoretical and experimental efforts, the properties leading to the higher denaturation temperature of hyperthermophilic proteins are still controversial. Among the large number of factors identified as responsible for the thermostability of hyperthermophilic proteins, the electrostatic interactions are thought to be a universally important factor.

Results

In this study, we report the effects of pH and salt concentration on the urea-induced denaturation of the protein Ssh10b from a hyperthermophile in low ionic strength buffer. In the absence of NaCl, the unfolding ΔG of the protein increased from about 33 kJ/mol at pH 3 to about 78 kJ/mol at pH 10. At all values of pH, the ΔG increased with increasing NaCl concentration, indicating that salt stabilizes the protein significantly.

Conclusion

These findings suggests that the increased number of charged residues and ion pairs in the protein Ssh10b from hyperthermophiles does not contribute to the stabilization of the folded protein, but may play a role in determining the denatured state ensemble and also in increasing the denaturation temperature.