title: Molecular basis for methoxyamine initiated mutagenesis. 1H nuclear magnetic resonance studies of base-modified oligodeoxynucleotides.
abstract: In order to reach a more detailed understanding of the mechanism of the mutagenic action of methoxyamine and of N4-methoxycytidine and its 2'-deoxyribo-analogue, the solution structures of the self-complementary octanucleotide, d(CGAATTCG) and its analogues, d(CGAATCCG), d(CGAATMCG) and d(CGAATPCG) (designated 8mer-AT, 8mer-AC, 8mer-AM, and 8mer-AP, respectively), were investigated by 1H nuclear magnetic resonance spectroscopy; M is N4-methoxycytosine (mo4C) and P is an analogue, the bicyclic dihydropyrimido[4,5-c][1,2]oxazin-7-one, in which the N-O bond is held in the anti configuration with respect to N3 of the cytosine ring. Correlated spectroscopy and nuclear Overhauser spectroscopy allowed assignment of the base, anomeric and H2'/H2" protons in 8mers-AT, -AM and -AP, and showed that all three had features consistent with a regular B-DNA duplex structure. Duplex-to-coil transition temperatures were determined to be 52(+/- 2) degrees C (8mer-AT), 51(+/- 2) degrees C (8mer-AP), 32(+/- 2) degrees C (8mer-AM); on the chemical shift timescale, the melting transition was fast for 8mer-AT and 8mer-AP, but slow for 8mer-AM. Imino proton spectra were indicative of Watson-Crick base-pairing in 8mers-AT, -AP and -AM. The 8mer-AP duplex had a structure and melting characteristics virtually identical with those of the 8mer-AT duplex. The preferred syn configuration of the methoxyl group in M had a destabilising effect on the 8mer-AM duplex. At low temperatures, the A.M base-pair was in fast equilibrium between Watson-Crick and wobble configurations, with the methoxyl function anti-oriented, but the melting transition was accompanied by isomerization of the methoxyl group to the syn conformation. This syn-anti isomerization was the rate-determining step in the duplex-to-coil transition. The 8mer-AC oligomer did not form a stable duplex.
authors.affiliation: University Chemical Laboratory Cambridge, U.K.
authors.forename: M J
authors.initials: MJ
authors.lastname: Stone
authors.forename: A N
authors.initials: AN
authors.lastname: Nedderman
authors.forename: D H
authors.initials: DH
authors.lastname: Williams
authors.forename: P K
authors.initials: PK
authors.lastname: Lin
authors.forename: D M
authors.initials: DM
authors.lastname: Brown
mesh_terms: D003562:Cytidine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D003903:Deuterium; D006358:Hot Temperature; D006898:Hydroxylamines / Q000737:chemistry* / Q000378:metabolism; D007097:Imines; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D016296:Mutagenesis; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry* / Q000378:metabolism; D011522:Protons
chemical_list: D006898:Hydroxylamines; D007097:Imines; D009838:Oligodeoxyribonucleotides; D011522:Protons; D003562:Cytidine; C017496:N(4)-methoxycytidine; C005214:methoxyamine; D003903:Deuterium