Thermal unfolding of the archaeal DNA and RNA binding protein Ssh10.
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.
Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
Xiaoqiu
X
Wu
Madalina
M
Oppermann
Kurt D
KD
Berndt
Tomas
T
Bergman
Hans
H
Jörnvall
Stefan
S
Knapp
Udo
U
Oppermann
D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D011489:Protein Denaturation; D017510:Protein Folding; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D016944:Sulfolobus / Q000378:metabolism*; D013816:Thermodynamics
D019843:Archaeal Proteins; D004268:DNA-Binding Proteins; D006657:Histones; D016601:RNA-Binding Proteins