title: Contribution of protein-surface ion pairs of a hyperthermophilic protein on thermal and thermodynamic stability.
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 degrees C and 77.4 kJ mol(-1) at 39.7 degrees 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 degrees C and 90.1 degrees C, respectively. The results suggest that the protein-surface ion pairs contribute to thermal stability (Tm), rather than thermodynamic stability (DeltaG).
authors.affiliation: School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Tatsunokuchi, Ishikawa 923-1292, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Shiraki
authors.forename: Shingo
authors.initials: S
authors.lastname: Nishikori
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Fujiwara
authors.forename: Tadayuki
authors.initials: T
authors.lastname: Imanaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Takagi