Abstract
BackgroundHyperthermophiles 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.ResultsIn 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.ConclusionThese 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.
Highlights
Hyperthermophiles constitute a group of microorganisms with an optimum growth temperature of between 80°C and 100°C
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 proteins from hyperthermophiles are still controversial [5]
A comparison of 13 structural parameters calculated from the tertiary structures of 64 proteins from mesophiles and 29 proteins from thermophiles and hyperthermophiles indicated that increases in the numbers of charged residues and ion pairs with increasing growth temperature and other parameters show just such a trend [6]
Summary
Hyperthermophiles constitute a group of microorganisms with an optimum growth temperature of between 80°C and 100°C. 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. BMC Biochemistry 2007, 8:28 http://www.biomedcentral.com/1471-2091/8/28 mostability of proteins from hyperthermophiles, electrostatic interactions have been proposed to be a universally important factor. A comparison of 13 structural parameters calculated from the tertiary structures of 64 proteins from mesophiles and 29 proteins from thermophiles and hyperthermophiles indicated that increases in the numbers of charged residues and ion pairs with increasing growth temperature and other parameters show just such a trend [6]. A theoretical analysis of charge interactions calculated using the Tanford-Kirkwood model applied to the protein crystal structures demonstrated a correlation between electrostatic interactions and thermostability [7]. Estimates of the energy contribution of an ion pair to protein stability have led to conflicting conclusions, ranging from stabilizing, through insignificant, to destabilizing effects [8,9,10]
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