title: Photoreactivation of DNA by an archaeal nucleoprotein Sso7d.
abstract: Sso7d is a chromosomal protein of hyperthermophilic Archaea. The crystal structure of Sso7d-d(GTAAT(I)UAC)(2) has been clarified at high resolution, showing that the protein binds in the minor groove of DNA, causing a sharp kink of approximately 60 degrees. Recently, we found that photoirradiation of Sso7d and 5-iodouracil-((I)U)-containing 5'-d(GTAAT(I)UAC)-3' efficiently induced the abstraction of hydrogen from the methyl group of T(5) at the kink. In the present study, we found that the photoreactivity of 5-bromouracil ((Br)U)-containing 5'-d(GTAAT(Br)UAC)-3' was enhanced in the presence of Sso7d. Using hypoxanthine (I)-containing 5'-d(ITAAT(Br)UAC)-3', we demonstrated that electron transfer occurs efficiently from Sso7d to DNA. Product analysis showed that Trp-24 of Sso7d, located at the surface of the DNA, is consumed to produce N'-formylkynurenine during photoirradiation, indicating that Trp-24 acts as an electron source. To explore the possibility of electron transfer between Sso7d and other DNA substrates, we examined the photochemical repair of the thymine dimer 5'-d(GTAAT<>TAC)-3' by Sso7d. Sso7d effectively repaired 5'-d(GTAAT<>TAC)-3' to 5'-d(GTAATTAC)-3' under irradiation conditions. During this reaction, Trp-24 was not oxidized significantly, indicating that the anion radical of the repaired TT sequence is oxidized by the cation radical of Trp-24, and that a so-called "circular electron transfer" mechanism is operating in this system.
authors.affiliation: Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
authors.forename: Ryu
authors.initials: R
authors.lastname: Tashiro
authors.forename: Andrew H-J
authors.initials: AH
authors.lastname: Wang
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sugiyama
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D001976:Bromouracil / Q000737:chemistry; D018360:Crystallography, X-Ray; D019641:DNA, Archaeal / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D004579:Electron Transport; D046911:Macromolecular Substances; D008954:Models, Biological; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009698:Nucleoproteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D018462:Photobiology; D011487:Protein Conformation; D011740:Pyrimidine Dimers / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D048229:Sulfolobus solfataricus / Q000378:metabolism; D014364:Tryptophan / Q000737:chemistry
chemical_list: D019843:Archaeal Proteins; D019641:DNA, Archaeal; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D009698:Nucleoproteins; D009838:Oligodeoxyribonucleotides; D011740:Pyrimidine Dimers; C093228:Sso7d protein, Sulfolobus; D001976:Bromouracil; D014364:Tryptophan