Dec 1, 1994

Thermodynamic characterization of an equilibrium folding intermediate of staphylococcal nuclease

Protein Science : a Publication of the Protein Society
D XieE Freire


High-sensitivity differential scanning calorimetry and CD spectroscopy have been used to probe the structural stability and measure the folding/unfolding thermodynamics of a Pro117-->Gly variant of staphylococcal nuclease. It is shown that at neutral pH the thermal denaturation of this protein is well accounted for by a 2-state mechanism and that the thermally denatured state is a fully hydrated unfolded polypeptide. At pH 3.5, thermal denaturation results in a compact denatured state in which most, if not all, of the helical structure is missing and the beta subdomain apparently remains largely intact. At pH 3.0, no thermal transition is observed and the molecule exists in the compact denatured state within the 0-100 degrees C temperature interval. At high salt concentration and pH 3.5, the thermal unfolding transition exhibits 2 cooperative peaks in the heat capacity function, the first one corresponding to the transition from the native to the intermediate state and the second one to the transition from the intermediate to the unfolded state. As is the case with other proteins, the enthalpy of the intermediate is higher than that of the unfolded state at low temperatures, indicating that, under those conditions, its stabiliz...Continue Reading

Mentioned in this Paper

Micrococcal Nuclease
Hyrex Brand of Dimenhydrinate
Protein Conformation
Calorimetry, Differential Scanning
Circular Dichroism, Vibrational
Protein Folding, Globular
Spectrum Analysis

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