Calculation of pigment transition energies in the FMO protein

Abstract

The Fenna-Matthews-Olson (FMO) protein of green sulfur bacteria represents an important model protein for the study of elementary pigment-protein couplings. We have previously used a simple approach [Adolphs and Renger (2006) Biophys J 91:2778-2797] to study the shift in local transition energies (site energies) of the FMO protein of Prosthecochloris aestuarii by charged amino acid residues, assuming a standard protonation pattern of the titratable groups. Recently, we have found strong evidence that besides the charged amino acids also the neutral charge density of the protein is important, by applying a combined quantum chemical/electrostatic approach [Müh et al. (2007) Proc Natl Acad Sci USA, in press]. Here, we extract the essential parts from this sophisticated method to obtain a relatively simple method again. It is shown that the main contribution to the site energy shifts is due to charge density coupling (CDC) between the pigments and their pigment, protein and water surroundings and that polarization effects for qualitative considerations can be approximated by screening the Coulomb coupling by an effective dielectric constant.

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

“…[124] The results in this study stressed the effect of the electric field induced by a helices. [124] The smaller effect in LHC-II was rationalized by antipodal dipole moments of the a helices.…”

“…[124] The results in this study stressed the effect of the electric field induced by a helices. [124] The smaller effect in LHC-II was rationalized by antipodal dipole moments of the a helices. [91] This interpretation is contradictory to the suggestion that only the first one or two turns of helices in a protein have a significant effect on the electrostatics.…”

“…[98-100, 121, 122]) and theoretically (see, e.g., ref. [104,[123][124][125]). System-specific aspects of these studies will be discussed in more detail in Section 6, while some general issues are addressed in the following.…”

Robustness, efficiency, and optimality in the Fenna-Matthews-Olson photosynthetic pigment-protein complex

“…For the eight-site FMO network considered here (i.e., n = 8 in Eq. (1)), the experimental site energies are known from fluorescence studies, 42,44 while the off-diagonal couplings have been determined by the transition dipole-dipole cube method. 6 In our treatment of the quantum dynamics of FMO-like systems, the electronic Hamiltonian of Eq.…”

Effect of complex inter-site couplings on the excitation energy transfer in the FMO complex

“…E j is the on-site energy of site j, and J ij denotes the inter-site coupling between sites i and j. The intersite couplings J ij given by J ij = d rΦ i ( r)ρ j ( r) represent the Coulomb couplings between the transition densities of the BChls [20], where Φ i ( r) is the electrostatic potential of the transition density of BChl i and ρ j ( r) is the transition density of BChl j. It is easy to find that this calculation can only give real inter-site couplings J ij .…”