On urea and temperature dependences of m-values

Area of Science:

• Biochemistry
• Chemical Physics
• Protein Science

Background:

• Protein structure stability is influenced by cosolvents through excluded volume and direct interactions.
• Urea is a common denaturant, and its effect on protein stability is well-studied.
• The m-value quantifies the change in denaturation free energy per unit change in denaturant concentration.

Purpose of the Study:

• To investigate the molecular origins of the weak temperature and urea dependence of globular protein m-values.
• To understand the compensatory effects governing protein-urea interactions.
• To assess the suitability of cosolvents for linear extrapolation model-based protein stability studies.

Main Methods:

• Combined experimental and computational approaches.
• Analysis of protein-cosolvent interactions.
• Characterization of solvent-accessible surface area changes.

Main Results:

• Protein m-values exhibit relative independence from urea concentration due to compensatory effects.
• The unfolded state shows increased solvent-accessible surface area and higher urea binding constants compared to the folded state.
• Increasing temperature reduces protein-urea binding constants, consistent with negative binding enthalpy.

Conclusions:

• Fortuitous compensation between unfolded state properties and urea binding explains the weak m-value dependence on urea concentration.
• Cosolvents lacking this compensation are unsuitable for linear extrapolation model-based stability studies.
• Temperature-dependent changes in binding constants contribute to the observed diminution of m-values with increasing temperature.