Collapse and Protein Folding: Should We Be Surprised That Biothermodynamics Works So Well?

Area of Science:

• Protein Thermodynamics
• Biophysics
• Structural Biology

Background:

• Understanding protein function necessitates characterizing all thermodynamic states, including the denatured state ensemble (DSE).
• Residual structure in partially folded states and the DSE influences protein thermodynamics and biological contexts.
• Investigating chain collapse and potential DSE property variations under different conditions is essential.

Purpose of the Study:

• To examine how DSE structure impacts protein thermodynamics.
• To analyze chain collapse in the context of DSE properties.
• To assess the consistency and robustness of DSE stability measurements.

Main Methods:

• Calorimetry
• Chemical denaturation
• Hydrogen-deuterium exchange

Main Results:

• Stability measurements using calorimetry and chemical denaturation are consistent with hydrogen-deuterium exchange.
• DSEs obtained via different perturbations are thermodynamically equivalent, serving as a common reference state.
• The DSE is characterized as a highly expanded ensemble with minimal stable hydrogen-bonded structure.

Conclusions:

• The robustness of stability measurements highlights the thermodynamic equivalence of DSEs.
• The expanded nature and minimal stable structure of the DSE are critical for applying thermodynamics to protein folding.
• These findings impact the understanding of protein folding mechanisms and pathways.