title: Structure-dependent DNA damage and repair in a trinucleotide repeat sequence.
abstract: Triplet repeat sequences, such as CAG/CTG, expand in the human genome to cause several neurological disorders. As part of the expansion process the formation of non-B DNA conformations by the repeat sequence has previously been proposed. Furthermore, the base excision repair enzyme 7,8-dihydro-8-oxoguanine glycosylase (OGG1) has recently been implicated in the repeat expansion [Kovtun, I. V., Liu, Y., Bjoras, M., Klugland, A., Wilson, S. H., and McMurray, C. T. (2007) Nature 447, 447-452]. In this work we have found that the non-B conformation adopted by (CAG)(10), a hairpin, is hypersusceptible to DNA damage relative to the (CAG)(10)/(CTG)(10) duplex and, in particular, that a hot spot for DNA damage exists. Specifically, we find that a single guanine in the loop of the hairpin is susceptible to modification by peroxynitrite. Interestingly, we find that human OGG1 (hOGG1) is able to excise 7,8-dihydro-8-oxoguanine (8-oxoG) from the loop of a hairpin substrate, albeit with a marked decrease in efficiency relative to duplex substrates; the hOGG1 enzyme removes 8-oxoG from the loop of a hairpin with a rate that is approximately 700-fold slower than that observed for DNA duplex. Thus, while damage is preferentially generated in the loop of the hairpin, DNA repair is less efficient. These observed structure-dependent patterns of DNA damage and repair may contribute to the OGG1-dependent mechanism of trinucleotide repeat expansion.
authors.affiliation: Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Jarem
authors.forename: Nicole R
authors.initials: NR
authors.lastname: Wilson
authors.forename: Sarah
authors.initials: S
authors.lastname: Delaney
mesh_terms: D001483:Base Sequence; D004249:DNA Damage; D045647:DNA Glycosylases / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation / Q000187:drug effects; D030421:Peroxynitrous Acid / Q000494:pharmacology; D013379:Substrate Specificity / Q000187:drug effects; D013997:Time Factors; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*
chemical_list: C453560:7,8-dihydro-8-oxoguanine; D030421:Peroxynitrous Acid; D006147:Guanine; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human