The low-temperature heat capacity of solid proteins.

Area of Science:

• Biophysics
• Thermodynamics
• Protein Dynamics

Background:

• Protein heat capacity is crucial for understanding molecular behavior.
• Harmonic models are commonly used to approximate protein dynamics and thermodynamic properties.

Purpose of the Study:

• To evaluate different harmonic models for calculating protein heat capacity.
• To investigate the influence of temperature, hydration, and conformational transitions on protein heat capacity.

Main Methods:

• Utilized inelastic neutron scattering, normal mode calculations, and the Debye model to obtain spectral densities.
• Analyzed heat capacity data across a wide temperature range (below 30 K to above 200 K).
• Compared theoretical predictions from various models with experimental data.

Main Results:

• All models showed reasonable agreement with experimental data, particularly above 100 K.
• Discrepancies below 30 K were observed, potentially due to discrete conformational transitions.
• Hydration significantly increased heat capacity above 200 K, linked to higher-energy conformational transitions.
• Cold denaturation was predicted to occur only with varying hydration levels.

Conclusions:

• Harmonic models provide a useful framework for understanding protein heat capacity.
• Conformational transitions and hydration are key factors influencing protein thermodynamic behavior.
• The study offers insights into phenomena like cold denaturation and the role of hydration in protein stability.