Preferential water exclusion in protein unfolding

Area of Science:

• Biochemistry
• Physical Chemistry
• Structural Biology

Background:

• Water-protein interactions are crucial for protein folding, stability, and function.
• Protein net charge, influenced by pH and side-chain ionization, significantly impacts these interactions.

Purpose of the Study:

• To investigate how varying net charges on cytochrome c affect its association with water.
• To quantify water exclusion during protein unfolding under different charge conditions.

Main Methods:

• Utilized equilibrium unfolding of cytochrome c in water-methanol mixtures.
• Varied protein charge by adjusting pH.
• Quantified preferential exclusion of water during unfolding.

Main Results:

• Water exclusion during unfolding correlated with net-charge-dependent molecular expansion.
• Water exclusion rate showed a linear relationship with protein unfolding rate when net charges were constant.
• Side-chain ionization and charge repulsion-induced expansion increase water-protein association.

Conclusions:

• Protein net charge and ionization state are key determinants of water association.
• Water exclusion is a significant factor influencing protein unfolding kinetics.
• Understanding these dynamics is vital for predicting protein behavior in biological systems.