Effect of Spectral Density Shapes on the Excitonic Structure and Dynamics of the Fenna–Matthews–Olson Trimer from Chlorobaculum tepidum

Abstract

The Fenna-Matthews-Olson (FMO) trimer (composed of identical subunits) from the green sulfur bacterium Chlorobaculum tepidum is an important protein model system to study exciton dynamics and excitation energy transfer (EET) in photosynthetic complexes. In addition, FMO is a popular model for excitonic calculations, with many theoretical parameter sets reported describing different linear and nonlinear optical spectra. Due to fast exciton relaxation within each subunit, intermonomer EET results predominantly from the lowest energy exciton states (contributed to by BChl a 3 and 4). Using experimentally determined shapes for the spectral densities, simulated optical spectra are obtained for the entire FMO trimer. Simultaneous fits of low-temperature absorption, fluorescence, and hole-burned spectra place constraints on the determined pigment site energies, providing a new Hamiltonian that should be further tested to improve modeling of 2D electronic spectroscopy data and our understanding of coherent and dissipation effects in this important protein complex.

Excitation energy transfer pathways in light‐harvesting proteins: Modeling with PyFREC

“…The mean unsigned errors (MUE) and maximal unsigned errors (MAX) are given in Table . As compared to previous studies the MUE and MAX values follow the trend: (largest error) model I > model II > model III (smallest error) which indicates similarity of structural information (molecular geometries) and computational methodologies used in Refs. [16, 19, 20, 33].…”

“…The excitation energies of BChl‐a pigments have previously been reported in multiple studies . Despite some discrepancies in absolute values of Q y excitation energies of FMO pigments, there is an agreement that BCL403 has the lowest excitation energy, BCL401, 402, 406, and 407 have higher energies than other FMO pigments.…”

“…s = 0.8 and exponential screening [eq. ] A = 2.68, β = 0.27 Å −1 , s 0 = 0.54 to compare with previous studies . The computed electronic couplings are presented in Table and Supporting Information Table S3.…”

“…Found in green sulfur bacteria, FMO is commonly utilized as a model system to study pigment–protein interactions due to its relative stability compared to other structures . The molecular structure of FMO has been identified and thoroughly investigated using X‐ray crystallography, electronic spectroscopy, and computational techniques . The structure of the FMO protein complex is unique, such that a trimer of identical subunits containing seven or eight bacteriochlorophyll‐a ( BChl‐a ) molecules constitute a complex, located between a large peripheral antenna, and the reaction center, forming a bridge for efficient charge separation and energy use .…”

Two-dimensional electronic spectra of the photosynthetic apparatus of green sulfur bacteria

“…BChl 6 and BChl 1 have been considered before as entry channel for energy flow from the chlorosome4. The more recent discovery of an eight chlorophyll in proximity of the baseplate and BChl 1 also suggest that this pigment links the chlorosome to the FMO3237. Both, the baseplate and the eight pigment have not been observed in 2DES1.…”