Configurationally-Coupled Protonation of Polyproline-7

Area of Science:

• Biochemistry
• Chemical Physics
• Thermodynamics

Background:

• Biomolecule-solvent interactions critically regulate protein structure and function.
• Thermodynamics of these interactions, particularly their influence on conformational entropy, remain poorly understood.

Purpose of the Study:

• To investigate the thermodynamics of biomolecule-solvent interactions.
• To elucidate the influence of these interactions on conformational entropy and proton transfer dynamics.

Main Methods:

• Kinetics and equilibrium measurements were performed at varying temperatures.
• Analysis of proton transfer reactions involving polyproline helices in a propanol:water solvent system.

Main Results:

• A slow proton transfer reaction coupled with a polyproline-I helix (PPI) to polyproline-II helix (PPII) conversion was observed.
• Thermodynamic parameters (ΔG, ΔH, ΔS) for both the overall and transition states of the proton transfer were determined.
• A minor non-protonating pathway was also characterized, yielding distinct thermodynamic values.

Conclusions:

• The study quantifies the thermochemistry of proton transfer and helix conversion in a mixed solvent system.
• Extraordinarily slow proton transfer is attributed to configurational coupling via a PPI-like transition state.
• Findings provide insight into the regulation of proton transfer influenced by solvent composition and biomolecular conformation.