title: Femtosecond dynamics of short-range protein electron transfer in flavodoxin.
abstract: Intraprotein electron transfer (ET) in flavoproteins is important for understanding the correlation of their redox, configuration, and reactivity at the active site. Here, we used oxidized flavodoxin as a model system and report our complete characterization of a photoinduced redox cycle from the initial charge separation in 135-340 fs to subsequent charge recombination in 0.95-1.6 ps and to the final cooling relaxation of the product(s) in 2.5-4.3 ps. With 11 mutations at the active site, we observed that these ultrafast ET dynamics, much faster than active-site relaxation, mainly depend on the reduction potentials of the electron donors with minor changes caused by mutations, reflecting a highly localized ET reaction between the stacked donor and acceptor at a van der Waals distance and leading to a gas-phase type of bimolecular ET reaction confined in the active-site nanospace. Significantly, these ultrafast ET reactions ensure our direct observation of vibrationally excited reaction product(s), suggesting that the back ET barrier is effectively reduced because of the decrease in the total free energy in the Marcus inverted region, leading to the accelerated charge recombination. Such vibrationally coupled charge recombination should be a general feature of flavoproteins with similar configurations and interactions between the cofactor flavin and neighboring aromatic residues.
authors.affiliation: Department of Physics, Department of Chemistry and Biochemistry, and Programs of Biophysics, Chemical Physics, and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Ting-Fang
authors.initials: TF
authors.lastname: He
authors.forename: Lijun
authors.initials: L
authors.lastname: Guo
authors.forename: Xunmin
authors.initials: X
authors.lastname: Guo
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Chang
authors.forename: Lijuan
authors.initials: L
authors.lastname: Wang
authors.forename: Dongping
authors.initials: D
authors.lastname: Zhong
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D016969:Desulfovibrio vulgaris / Q000378:metabolism; D004583:Electrons; D005486:Flavin Mononucleotide / Q000737:chemistry / Q000378:metabolism*; D005418:Flavodoxin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction / Q000528:radiation effects; D055668:Photochemical Processes; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism*; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D005418:Flavodoxin; D050505:Mutant Proteins; D014443:Tyrosine; D005486:Flavin Mononucleotide; D014364:Tryptophan