tailieunhanh - Báo cáo khoa học: The conformational stability of the Streptomyces coelicolor histidine-phosphocarrier protein Characterization of cold denaturation and urea–protein interactions

Thermodynamic parameters describing the conformational stability of the histidine-containing phosphocarrier protein fromStreptomyces coelicolor, scHPr, have been determined by steady-state fluorescence measurements of isothermal urea-denaturations, differential scanning calorimetry at different guanidinium hydrochloride concentrations and, independently, by far-UV circular dichroism measurements of isothermal urea-denaturations, and thermal denatura-tions at fixed urea concentrations. | Eur. J. Biochem. 271 2165-2181 2004 FEBS 2004 doi The conformational stability of the Streptomyces coelicolor histidine-phosphocarrier protein Characterization of cold denaturation and urea-protein interactions Jose L. Neira1 2 and Javier Gomez1 1Instituto de Biologia Molecular y Celular Universidad Miguel Hernandez Elche Alicante 2Instituto de Biocomputacion y Fisica de los Sistemas complejos Zaragoza Spain Thermodynamic parameters describing the conformational stability of the histidine-containing phosphocarrier protein from Streptomyces coelicolor scHPr have been determined by steady-state fluorescence measurements of isothermal urea-denaturations differential scanning calorimetry at different guanidinium hydrochloride concentrations and independently by far-UV circular dichroism measurements of isothermal urea-denaturations and thermal denaturations at fixed urea concentrations. The equilibrium unfolding transitions are described adequately by the two-state model and they validate the linear free-energy extrapolation model over the large temperature range explored and the urea concentrations used. At moderate urea concentrations from 2 to 3 m scHPr undergoes both high- and low-temperature unfolding. The free-energy stability curves have been obtained for the whole temperature range and values of the thermodynamic parameters governing the heat- and cold-denaturation processes have been obtained. Colddenaturation of the protein is the result of the combination of an unusually high heat capacity change kcal-mol-1-K-1 at 0 M urea being the average of the fluorescence circular dichroism and differential scanning calorimetry measurements and a fairly low enthalpy change upon unfolding at the midpoint temperature of heat-denaturation 59 4 kcal-mol-1 the average of the fluorescence circular dichroism and differential scanning calorimetry measurements . The changes in enthalpy mDHj entropy mASi and heat capacity mACpi which occur