Charge transfer through a cytochrome multiheme chain: theory and simulation.
We study sequential charge transfer within a chain of four heme cofactors located in the c-type cytochrome subunit of the photoreaction center of Rhodopseudomonas viridis from a theoretical perspective. Molecular dynamics simulations of the thermodynamic integration type are used to compute two key energies of Marcus' theory of charge transfer, the driving force ∆G and the reorganization energy λ. Due to the small exposure of the cofactors to the solvent and to charged amino acids, the outer sphere contribution to the reorganization energy almost vanishes. Interheme effective electronic couplings are estimated using ab initio wave functions and a well-parameterized semiempirical scheme for long-range interactions. From the resulting charge transfer rates, we conclude that at most the two heme molecules closest to the membrane participate in a fast recharging of the photoreaction center, whereas the remaining hemes are likely to have a different function, such as intermediate electron storage. Finally, we suggest means to verify or falsify this hypothesis.
Institut für Physikalische Chemie, Universität Freiburg, Albertstraße 23a, D-79104 Freiburg im Breisgau, Germany; Institut für Technische Thermodynamik, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Pfaffenwaldring 38-40, D-70569 Stuttgart, Germany.
Fabian
F
Burggraf
Thorsten
T
Koslowski
D000596:Amino Acids / Q000737:chemistry; D045304:Cytochromes c / Q000737:chemistry*; D004579:Electron Transport; D004583:Electrons; D004734:Energy Metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D012241:Rhodopseudomonas / Q000737:chemistry; D013816:Thermodynamics
D000596:Amino Acids; D006418:Heme; D045304:Cytochromes c
Charge transfer; Marcus theory; Molecular dynamics; Photoreaction center; Rps. viridis; Simulations