Protein electron transfer: is biology (thermo)dynamic?

Understanding energy flow in biological systems remains a central challenge. Energy enters cells via electrons in high-energy states, either from food or light. This energy is converted into proton-motive forces that power cellular processes. Despite this, the efficiency of electron transfer in proteins remains poorly understood. Synthetic systems have not matched the near-zero energy loss seen in biology. Current knowledge focuses on the role of proton gradients and electron transport chains. However, the physical mechanisms enabling this efficiency are unclear. The protein-water interface is a key but underexplored area. Fluctuations at this interface may influence electron transfer dynamics. This gap motivated a deeper investigation into the interplay between protein structure and electrostatic interactions. The role of electrostatic fluctuations in modulating chemical reactivity remains uncertain.

This review aims to clarify how proteins achieve efficient electron transfer. The specific problem is the lack of understanding about the physical mechanisms behind energy transfer in biological systems. The motivation comes from the need to explain how proteins maintain high efficiency without significant energy loss. The study focuses on the protein-water interface and its electrostatic properties. It seeks to determine if this interface produces unique electrostatic signatures. The goal is to link these signatures to the control of chemical reactivity. The study also investigates how ergodicity breaking affects reaction rates. By addressing these questions, the paper aims to provide a framework for understanding electron transfer in proteins.

The review synthesizes existing literature on protein dynamics and electrostatic interactions. It examines the physical mechanisms behind protein folding and energy landscapes. The study uses computational models to analyze protein-water interfaces. These models consider elastic flexibility and surface charge distributions. The focus is on how these factors polarize water dipoles into nanodomains. The review also incorporates experimental data on electrostatic fluctuations. It evaluates how these fluctuations influence chemical reactivity. The methods include statistical analysis of relaxation times and ergodicity breaking.

Proteins exhibit a rugged energy landscape with broad relaxation times. The protein-water interface is structurally and dynamically heterogeneous. Surface charges polarize water dipoles into nanodomains. Electrostatic fluctuations at this interface are critical to protein function. These fluctuations influence the activation free energy of reactions. Ergodicity is often broken in protein-driven reactions. Nonergodic activated kinetics extends transition-state theory. This formalism accounts for dynamically dispersive media. Reaction rates are optimized by the protein-water thermal bath dynamics. Free energy alone does not fully explain biological efficiency.

The study highlights the role of electrostatic fluctuations in protein function. It suggests that bath dynamics are as important as free energy in optimizing biological performance. The findings indicate that ergodicity breaking is a key factor in reaction control. Nonergodic activated kinetics provides a framework for understanding this. The protein-water interface plays a central role in modulating chemical reactivity. These conclusions align with the authors' emphasis on dynamic control mechanisms. The study does not propose new drug targets or future directions. Instead, it underscores the need for further investigation into protein-water electrostatic interactions.