Static Disorder in Excitation Energies of the Fenna-Matthews-Olson Protein: Structure-Based Theory Meets Experiment.

Marten L Chaillet,Frank Müh,Thomas Renger,Florian Lengauer,Alex W Chin,Julian Adolphs,Alexander S Fokas,Daniel J Cole

doi:10.1021/acs.jpclett.0c03123

Abstract

Inhomogeneous broadening of optical lines of the Fenna–Matthews–Olson (FMO) light-harvesting protein is investigated by combining a Monte Carlo sampling of low-energy conformational substates of the protein with a quantum chemical/electrostatic calculation of local transition energies (site energies) of the pigments. The good agreement between the optical spectra calculated for the inhomogeneous ensemble and the experimental data demonstrates that electrostatics is the dominant contributor to static disorder in site energies. Rotamers of polar amino acid side chains are found to cause bimodal distribution functions of site energy shifts, which can be probed by hole burning and single-molecule spectroscopy. When summing over the large number of contributions, the resulting distribution functions of the site energies become Gaussians, and the correlations in site energy fluctuations at different sites practically average to zero. These results demonstrate that static disorder in the FMO protein is in the realm of the central limit theorem of statistics.

Highlights

Inhomogeneous broadening of optical lines of the Fenna− Matthews−Olson (FMO) light-harvesting protein is investigated by combining a Monte Carlo sampling of low-energy conformational substates of the protein with a quantum chemical/electrostatic calculation of local transition energies of the pigments
Major progress concerning the site energies was obtained by Aartsma and co-workers,[16] who recognized that using a smaller effective dipole strength of the pigments in the calculation of excitonic couplings allows one to find site energies that fit linear absorption, linear dichroism, and circular dichroism spectra
It was recognized that there is a gradient in local transition energies toward BChls 3 and 4, which are located on one side of the FMO protein

Summary

Introduction

Inhomogeneous broadening of optical lines of the Fenna− Matthews−Olson (FMO) light-harvesting protein is investigated by combining a Monte Carlo sampling of low-energy conformational substates of the protein with a quantum chemical/electrostatic calculation of local transition energies (site energies) of the pigments.

Results

Conclusion