On the influence of pigment-protein interactions on the energy transfer processes in photosynthetic membrane structures

Low-temperature heterogeneous absorption and circular dichroism spectra of the Prosthecochloris aestuarii FMO complex were calculated within the framework of the mini-exciton theory including both the inhomogeneous distribution of exciton line frequencies and static random disorder of the pure electronic transitions of Bchl molecules. The frequencies of the Qy pure electronic transitions of Bchl molecules immobilized by the FMO complex polypeptides were found by minimization of a functional which links the parameters of the theoretical and experimental optical spectra. The interactions of Bchl molecules with surrounding amino acid residues was shown to change both the exciton delocalization index and exciton distribution between the pigment molecules in each exciton energetic state. As a consequence, the interlevel exciton relaxation processes, being accompanied by essential changes in the exciton distribution between pigment molecules, lead to the energy transfer within the FMO complex. The model spectra calculations within the framework of the static random disorder approach were shown to give unacceptable results.