Solvent effects on horse apomyoglobin dynamics.

This study investigates how different solvent conditions impact the protein dynamics of horse apomyoglobin, monitored through tryptophan fluorescence. The research unveils that changes in pH and added substances like ethanol or formamide result in structural changes and can influence the hydration state of the protein, potentially affecting the protein’s overall dynamics.

Research Context and Methodology

• The researchers studied the protein dynamics of horse apomyoglobin under various solvent conditions, including different pH levels (7, 8, and 9) and the addition of other substances like 3.2% ethanol or 6.2% formamide.
• Tryptophan fluorescence quenching, spectra, and decay properties were used as methodologies to monitor the changes in the protein.

Key Findings

• Increasing the pH encourages structural fluctuations within the hydrophobic core of the A, G, and H helix in the protein, a process facilitated by discontinuous protein conformation changes.
• Solutions containing 3.2% ethanol or 6.2% formamide generate alterations in the protein dynamics around the two tryptophan (Trp) residues. However, these substances do not induce specific constraints on these residues.
• Formamide boosts the polarity and flexibility of the protein, whereas ethanol reduces both. This suggests that these substances impact the distribution of water molecules on the protein surface, causing subsequent changes in protein dynamics.

Observations on Trp Residues and Hydrogen-Tritium Exchange

• The study revealed that regardless of the external solvent used, the two Trp residues (W7 and W14), situated within the A, G, H helix core, are uniformly and statistically reached by smaller molecules diffusing into the protein matrix.
• Hydrogen-tritium exchange measurements show that the dynamics of the A, G, and H helix cluster, and of the B and E helices, are significantly influenced by the nature of the external solution. In other words, the presence of certain substances, even in minor quantities, can induce notable effects on the protein dynamics.
• Presence of formamide in the buffer augments protein fluctuations, while an ethanol-water mixture reduces them.

Implications

• The research indicates that the hydration state of the protein surface might be a critical factor in determining the protein dynamics. This finding might have broader implications and contribute to a more nuanced understanding of how solvent conditions affect proteins.