A novel vicinal lesion obtained from the oxidative photosensitization of TpdG: characterization and mechanistic aspects.
A new type of vicinal base lesion was isolated from the photosensitization of TpdG in aerated aqueous solution. One- and two-dimensional NMR measurements were used together with mass spectrometry to accurately characterize the new adduct. Chemical detection of guanidine provided additional structural information on the base moiety at the 3'-OH terminal end. Altogether the experiments results were indicative of the occurrence of a covalent bonding between the pyrimidine ring on the 5'-OH terminal end and the imidazole ring on the 3'-OH terminal end through a methylene bridge. Photosensitization studies of TpdG, thymidine, and 2'-deoxyguanosine in the presence of either benzophenone, menadione, or riboflavin associated with isotopic labeling experiments using enriched oxygen and water provided relevant information on the mechanism of formation of the adduct. The results of these experiments clearly demonstrated that the initial event leading to the formation of the lesion is the abstraction of a hydrogen atom from the methyl group of the thymine base moiety of TpdG. This is followed by the addition of the methyl-centered radical to the C-4 atom of the guanine ring which gives rise to the vicinal lesion after reaction with molecular oxygen and subsequent rearrangement.
Département de Recherche Fondamentale sur la Matière Condensée, SCIB/Laboratoire des Lésions des Acides Nucléiques, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France.
T
T
Delatour
T
T
Douki
D
D
Gasparutto
M C
MC
Brochier
J
J
Cadet
D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000378:metabolism / Q000528:radiation effects; D018736:DNA Adducts / Q000737:chemistry; D004249:DNA Damage; D003849:Deoxyguanosine / Q000737:chemistry*; D015226:Dinucleoside Phosphates / Q000737:chemistry* / Q000528:radiation effects*; D006147:Guanine / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D010777:Photochemistry; D013936:Thymidine / Q000737:chemistry*; D014466:Ultraviolet Rays
D018736:DNA Adducts; D015226:Dinucleoside Phosphates; C077117:thymidylyl-(3',5')-2'-deoxyguanosine; D006147:Guanine; D004247:DNA; D003849:Deoxyguanosine; D013936:Thymidine