title: Determining complete electron flow in the cofactor photoreduction of oxidized photolyase.
abstract: The flavin cofactor in photoenzyme photolyase and photoreceptor cryptochrome may exist in an oxidized state and should be converted into reduced state(s) for biological functions. Such redox changes can be efficiently achieved by photoinduced electron transfer (ET) through a series of aromatic residues in the enzyme. Here, we report our complete characterization of photoreduction dynamics of photolyase with femtosecond resolution. With various site-directed mutations, we identified all possible electron donors in the enzyme and determined their ET timescales. The excited cofactor behaves as an electron sink to draw electron flow from a series of encircling aromatic molecules in three distinct layers from the active site in the center to the protein surface. The dominant electron flow follows the conserved tryptophan triad in a hopping pathway across the layers with multiple tunneling steps. These ET dynamics occur ultrafast in less than 150 ps and are strongly coupled with local protein and solvent relaxations. The reverse electron flow from the flavin is slow and in the nanosecond range to ensure high reduction efficiency. With 12 experimentally determined elementary ET steps and 6 ET reaction pairs, the enzyme exhibits a distinct reduction-potential gradient along the same aromatic residues with favorable reorganization energies to drive a highly unidirectional electron flow toward the active-site center from the protein surface.
authors.affiliation: Department of Physics, Ohio State University, Columbus, OH 43210, USA.
authors.forename: Zheyun
authors.initials: Z
authors.lastname: Liu
authors.forename: Chuang
authors.initials: C
authors.lastname: Tan
authors.forename: Xunmin
authors.initials: X
authors.lastname: Guo
authors.forename: Jiang
authors.initials: J
authors.lastname: Li
authors.forename: Lijuan
authors.initials: L
authors.lastname: Wang
authors.forename: Aziz
authors.initials: A
authors.lastname: Sancar
authors.forename: Dongping
authors.initials: D
authors.lastname: Zhong
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D020134:Catalytic Domain; D056931:Cryptochromes / Q000737:chemistry / Q000378:metabolism; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004579:Electron Transport / Q000528:radiation effects; D004735:Energy Transfer; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry* / Q000378:metabolism; D005415:Flavins / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D009154:Mutation; D010084:Oxidation-Reduction / Q000528:radiation effects; D055668:Photochemical Processes; D013053:Spectrophotometry; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D056931:Cryptochromes; D029968:Escherichia coli Proteins; D005415:Flavins; D005182:Flavin-Adenine Dinucleotide; D014364:Tryptophan; D004255:Deoxyribodipyrimidine Photo-Lyase
keywords: electron flow directionality; femtosecond dynamics; flavin photoreduction; protein electron transfer; reduction potential funnel