Electrostatic interaction between redox cofactors in photosynthetic reaction centers.
Intramolecular electron transfer within proteins is an essential process in bioenergetics. Redox cofactors are embedded in proteins, and this matrix strongly influences their redox potential. Several cofactors are usually found in these complexes, and they are structurally organized in a chain with distances between the electron donor and acceptor short enough to allow rapid electron tunneling. Among the different interactions that contribute to the determination of the redox potential of these cofactors, electrostatic interactions are important but restive to direct experimental characterization. The influence of interaction between cofactors is evidenced here experimentally by means of redox titrations and time-resolved spectroscopy in a chimeric bacterial reaction center (Maki, H., Matsuura, K., Shimada, K., and Nagashima, K. V. P. (2003) J. Biol. Chem. 278, 3921-3928) composed of the core subunits of Rubrivivax gelatinosus and the tetraheme cytochrome of Blastochloris viridis. The absorption spectra and orientations of the various cofactors of this chimeric reaction center are similar to those found in their respective native protein, indicating that their local environment is conserved. However, the redox potentials of both the primary electron donor and its closest heme are changed. The redox potential of the primary electron donor is downshifted in the chimeric reaction center when compared with the wild type, whereas, conversely, that of its closet heme is upshifted. We propose a model in which these reciprocal shifts in the midpoint potentials of two electron transfer partners are explained by an electrostatic interaction between them.
Alric
Jean
J
Laboratoire de Génétique et Biophysique des Plantes, UMR 6191 CNRS-CEA-Aix-Marseille II, 163 avenue de Luminy, Marseille 13288, France.
Cuni
Aude
A
Maki
Hideaki
H
Nagashima
Kenji V P
KV
Verméglio
André
A
Rappaport
Fabrice
F
D003067:Coenzymes / Q000737:chemistry* / Q000378:metabolism; D004563:Electrochemistry; D004579:Electron Transport / Q000502:physiology*; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012241:Rhodopseudomonas / Q000378:metabolism; D055672:Static Electricity
D003067:Coenzymes; D045322:Photosynthetic Reaction Center Complex Proteins; D011993:Recombinant Fusion Proteins