Protein Electron Transfer in Solution, Protein Powders, and Electrode Confinement

Area of Science:

• Biophysics
• Electrochemistry
• Computational Biology

Background:

• Biological electron transport chains involve interfaces and confinement.
• Protein electron transfer rates are typically measured in solution, limiting understanding of confined environments.

Purpose of the Study:

• To compare electron transfer activation parameters of the azurin protein in solution versus confinement.
• To model electrochemical experimental conditions using protein powders and gold slab confinement.

Main Methods:

• Molecular dynamics simulations of the azurin protein.
• Inclusion of active site polarizability in calculations.
• Modeling confinement between two gold slabs and in protein powders.

Main Results:

• Protein active site polarizability is key in lowering the electron transfer activation barrier.
• Strong electric fields in confinement lead to a reorganization energy of ~0.1-0.2 eV.
• Low activation barriers (~2kBT) result in a weak temperature dependence of the reaction rate.

Conclusions:

• Confinement and active site polarizability modulate protein electron transfer.
• Calculations show no dynamical medium control of protein half-reactions.
• Electron transfer rates decay exponentially with distance to the electrode.