Thermodynamics of the unfolding of the cold-shock protein from Thermotoga maritima.
Proteins from (hyper-)thermophiles are known to exhibit high intrinsic stabilities. Commonly, their thermodynamic characterization is impeded by irreversible side reactions of the thermal analysis or calorimetrical problems. Small single-domain proteins are suitable candidates to overcome these obstacles. Here, the thermodynamics of the thermal denaturation of the recombinant cold-shock protein (Csp) from the hyperthermophilic bacterium Thermotoga maritima (Tm) was studied by differential scanning calorimetry. The unfolding transition can be described over a broad pH range (3.5-8.5) by a reversible two-state process. Maximum stability (DeltaG (25 degrees C)=6.5 kcal/mol) was observed at pH 5-6 where Tm Csp unfolds with a melting temperature at 95 degrees C. The heat capacity difference between the native and the denatured states is 1.1(+/-0.1) kcal/(mol K). At pH 7, thermal denaturation occurs at 82 degrees C. The corresponding free energy profile has its maximum at 30 degrees C with DeltaGN-->U=4.8(+/-0.5) kcal/mol. At the optimal growth temperature of T. maritima (80 degrees C), Tm Csp in the absence of ligands is only marginally stable, with a free energy of stabilization not far beyond the thermal energy. With the known stabilizing effect of nucleic acids in mind, this suggests a highly dynamical interaction of Tm Csp with its target molecules.
Wassenberg
D
D
Institut für Biophysik und Physikalische Biochemie, Universität Regensburg, Regensburg, D-93040, Germany.
Welker
C
C
Jaenicke
R
R
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002152:Calorimetry, Differential Scanning; D003001:Cloning, Molecular; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011489:Protein Denaturation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics; D020124:Thermotoga maritima / Q000378:metabolism*
D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; D011994:Recombinant Proteins