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The reversible thermal unfolding of the archaeal histone-like protein Ssh10b from the extremophile Sulfolobus shibatae was studied using differential scanning calorimetry and circular dichroism spectroscopy. Analytical ultracentrifugation and gel filtration showed that Ssh10b is a stable dimer in the pH range 2.5-7.0. Thermal denaturation data fit into a two-state unfolding model, suggesting that the Ssh10 dimer unfolds as a single cooperative unit with a maximal melting temperature of 99.9 degrees C and an enthalpy change of 134 kcal/mol at pH 7.0. The heat capacity change upon unfolding determined from linear fits of the temperature dependence of DeltaH(cal) is 2.55 kcal/(mol K). The low specific heat capacity change of 13 cal/(mol K residue) leads to a considerable flattening of the protein stability curve (DeltaG (T)) and results in a maximal DeltaG of only 9.5 kcal/mol at 320 K and a DeltaG of only 6.0 kcal/mol at the optimal growth temperature of Sulfolobus.

Original publication

DOI

10.1016/j.bbrc.2008.06.030

Type

Journal article

Journal

Biochemical and biophysical research communications

Publication Date

09/2008

Volume

373

Pages

482 - 487

Addresses

Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden.

Keywords

Sulfolobus, Archaeal Proteins, RNA-Binding Proteins, DNA-Binding Proteins, Histones, Calorimetry, Differential Scanning, Circular Dichroism, Amino Acid Sequence, Protein Denaturation, Protein Folding, Hydrogen-Ion Concentration, Thermodynamics, Molecular Sequence Data, Hot Temperature