title: Asymmetric electron transfer in cyanobacterial Photosystem I: charge separation and secondary electron transfer dynamics of mutations near the primary electron acceptor A0.
abstract: Point mutations were introduced near the primary electron acceptor sites assigned to A0 in both the PsaA and PsaB branches of Photosystem I in the cyanobacterium Synechocystis sp. PCC 6803. The residues Met688PsaA and Met668PsaB, which provide the axial ligands to the Mg2+ of the eC-A3 and eC-B3 chlorophylls, were changed to leucine and asparagine (chlorophyll notation follows Jordan et al., 2001). The removal of the ligand is expected to alter the midpoint potential of the A0/A0- redox pair and result in a change in the intrinsic charge separation rate and secondary electron transfer kinetics from A0- to A1. The dynamics of primary charge separation and secondary electron transfer were studied at 690 nm and 390 nm in these mutants by ultrafast optical pump-probe spectroscopy. The data reveal that mutations in the PsaB branch do not alter electron transfer dynamics, whereas mutations in the PsaA branch have a distinct effect on electron transfer, slowing down both the primary charge separation and the secondary electron transfer step (the latter by a factor of 3-10). These results suggest that electron transfer in cyanobacterial Photosystem I is asymmetric and occurs primarily along the PsaA branch of cofactors.
authors.affiliation: Department of Physics, Purdue University, West Lafayette, Indiana.
authors.forename: Naranbaatar
authors.initials: N
authors.lastname: Dashdorj
authors.forename: Wu
authors.initials: W
authors.lastname: Xu
authors.forename: Rachel O
authors.initials: RO
authors.lastname: Cohen
authors.forename: John H
authors.initials: JH
authors.lastname: Golbeck
authors.forename: Sergei
authors.initials: S
authors.lastname: Savikhin
mesh_terms: D019943:Amino Acid Substitution; D004579:Electron Transport / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D016297:Mutagenesis, Site-Directed; D045331:Photosystem I Protein Complex / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects*; D013056:Spectrophotometry, Ultraviolet; D055672:Static Electricity; D013329:Structure-Activity Relationship
chemical_list: D045331:Photosystem I Protein Complex