Thermodynamic characterization of an equilibrium folding intermediate of staphylococcal nuclease.


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 stabilization must be of an entropic origin. The folding intermediate has been modeled by structural thermodynamic calculations. Structure-based thermodynamic calculations also predict that the most probable intermediate is one in which the beta subdomain is essentially intact and the rest of the molecule unfolded, in agreement with the experimental data. The structural features of the equilibrium intermediate are similar to those of a kinetic intermediate previously characterized by hydrogen exchange and NMR spectroscopy. Study holds ProTherm entries: 11306, 11307, 11308, 11309, 11310 Extra Details: additive : EDTA(1 mM), differential scanning calorimetry; protein folding,intermediates; structural thermodynamics

Submission Details

ID: hsyvsJiQ3

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:42 p.m.

Version: 1

Publication Details
Xie D;Fox R;Freire E,Protein Sci. (1994) Thermodynamic characterization of an equilibrium folding intermediate of staphylococcal nuclease. PMID:7756977
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Thermonuclease P00644 NUC_STAAU
99.3 Thermonuclease Q5HHM4 NUC_STAAC
99.1 Thermonuclease Q99VJ0 NUC_STAAM
99.1 Thermonuclease Q7A6P2 NUC_STAAN
99.3 Thermonuclease Q6GB41 NUC_STAAS
99.3 Thermonuclease Q8NXI6 NUC_STAAW
99.3 Thermonuclease Q6GIK1 NUC_STAAR