Thermal denaturation of staphylococcal nuclease

Area of Science:

• Biochemistry
• Protein Chemistry
• Biophysical Chemistry

Background:

• Staphylococcal nuclease is a model enzyme for studying protein folding and stability.
• Understanding protein-ligand interactions is crucial for protein function and drug design.

Purpose of the Study:

• To investigate the thermal denaturation of staphylococcal nuclease.
• To determine the effects of calcium (Ca2+) and thymidine 3',5'-diphosphate (pdTp) on protein stability.
• To quantify the binding constants and enthalpies of these ligands.

Main Methods:

• High-sensitivity differential scanning calorimetry (DSC) was employed.
• Thermal denaturation was studied across a pH range of 4 to 8.
• The effects of Ca2+ and pdTp, alone and in combination, were analyzed.

Main Results:

• Unliganded staphylococcal nuclease denaturation showed typical values for small globular proteins.
• Both Ca2+ and pdTp individually stabilized the protein, with synergistic effects when both were present.
• Ligand binding increased denaturational enthalpy and melting temperature (tm) by up to 11°C.
• Binding constants at 53°C were estimated as 950 M-1 for Ca2+ and 1.4 x 10(4) M-1 for pdTp.
• Binding enthalpies at 53°C were -15.0 kcal mol-1 for Ca2+ and -19.3 kcal mol-1 for pdTp.

Conclusions:

• Ca2+ and pdTp significantly stabilize staphylococcal nuclease against thermal denaturation.
• The study provides quantitative data on the binding thermodynamics of these ligands.
• Findings contribute to the understanding of ligand-induced protein stabilization.