Composition dependent multiple structural transformations of myoglobin in aqueous ethanol solution: a combined...

Area of Science:

• Biophysics
• Protein structural dynamics
• Solution chemistry

Background:

• Proteins exhibit complex conformational behavior in mixed solvent systems.
• Understanding protein structure in non-native environments is crucial for biochemistry.
• Aqueous ethanol mixtures are known to induce structural transformations.

Purpose of the Study:

• To investigate the structural transformations of myoglobin in aqueous ethanol mixtures.
• To identify specific ethanol concentrations that induce significant conformational changes.
• To characterize the intermediate states formed during these transformations.

Main Methods:

• Combined experimental techniques: circular dichroism and UV-Vis absorption spectroscopy.
• Large-scale atomistic molecular dynamics simulations.
• Order parameter analyses including radius of gyration and contact order.

Main Results:

• Identified two distinct structural regimes at xEtOH ~ 0.05 and xEtOH ~ 0.25, with a partially unfolded intermediate at xEtOH ~ 0.15.
• Observed non-monotonic composition dependence for radius of gyration, contact order, solvent accessible surface area, and spectral properties.
• Characterized the intermediate state at xEtOH ~ 0.15 as a molten globule based on minimum contact order parameter.

Conclusions:

• Ethanol-water mixtures induce remarkable and unforeseen structural transformations in myoglobin.
• The protein's conformation and dynamics are strongly affected by the binary mixture composition.
• Comparison with water-dimethyl sulfoxide mixtures suggests general principles for co-solvent effects on protein structure.