Probing static disorder in Arrhenius kinetics by single-molecule force spectroscopy

Area of Science:

• Chemical Kinetics
• Biophysics
• Statistical Mechanics

Background:

• The Arrhenius equation traditionally models simple two-state reactions with a single transition state and activation energy barrier.
• Real-world reactions often exhibit nonexponential kinetics due to ensembles of conformations at the transition state, challenging the classical model.
• Understanding these complex kinetics is crucial for interpreting single-molecule experimental data.

Purpose of the Study:

• To generalize the Arrhenius equation to incorporate static disorder from conformational ensembles.
• To develop a theoretical framework for understanding nonexponential kinetics under external perturbations.
• To validate the theory using single-molecule experiments on protein unfolding.

Main Methods:

• Development of a generalized Arrhenius equation theory accounting for static disorder and external perturbations.
• Utilizing force-clamp spectroscopy to probe single ubiquitin protein unfolding kinetics.
• Analyzing the force-dependent and independent components of the activation energy barrier variance.

Main Results:

• The generalized theory accurately predicts nonexponential kinetics arising from conformational disorder.
• Force-clamp spectroscopy data for ubiquitin unfolding showed variance in activation energy (DeltaE) with force-dependent and independent contributions.
• The force-dependent component of DeltaE variance scaled with F(2), matching theoretical predictions.

Conclusions:

• The study presents a novel adaptation of the Arrhenius equation that explains nonexponential kinetics at the microscopic level.
• The findings highlight the importance of considering static disorder and conformational ensembles in reaction kinetics.
• The developed theory provides a robust framework for analyzing single-molecule data in biophysics and chemistry.