Review
Contribution of protein-surface ion pairs of a hyperthermophilic protein on thermal and thermodynamic stability

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Abstract

Hyperthermophilic proteins possess many ion pairs on their surface. To reveal the role of the ion pairs, O6-methylguanine-DNA methyltransferase from Thermococcus kodakaraensis KOD1 (Tk-MGMT) was studied as a model protein. The maximum free-energy changes of the protein in 0.1 and 0.5 M NaCl at pH 7.0 were 61.7 kJ mol−1 at 31.5°C and 77.4 kJ mol−1 at 39.7°C, respectively. On the other hand, mid points of the thermal unfolding temperatures in 0.1 and 0.5 M NaCl at pH 7.0 were 94.8°C and 90.1°C, respectively. The results suggest that the protein-surface ion pairs contribute to thermal stability (Tm), rather than thermodynamic stability (ΔG).

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Acknowledgments

This work was undertaken with a partial support from Japan Science and Technology Corporation (JST) for Core Research for Evolutional Science and Technology (CREST).

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