title: Probing the conformational heterogeneity of the acetylaminofluorene-modified 2'-deoxyguanosine and DNA by 19F NMR spectroscopy.
abstract: 19F NMR spectroscopy was used to probe the conformation of a DNA adduct derived from the carcinogen 7-fluoro-N-acetyl-2-aminofluorene (FAAF) in three structural contexts: as a monomer and incorporated into single- and double-stranded DNA. The 19F NMR spectrum of dG-C8-FAAF [N-(deoxyguanosin-8-yl)-N-acetyl-7-fluoro-2-aminofluorene] in methanol at -30 degrees C exhibited four interconvertible signals in a 11:52:26:11 ratio. Dynamic NMR analysis indicated that the four torsional isomers arise from restricted rotation about the amide (gamma) (14.4 kcal/mol) and the guanyl-nitrogen (alpha) bonds. The conformational heterogeneity persisted in a single strand FAAF-12-mer, d(CTTCTTG[FAAF]ACCTC), whose 19F NMR spectrum at 22 degrees C and pH 7.0 gave only two signals in a 40:60 ratio, instead of four. The two 19F signals followed a two-site exchange with the rotation barrier of 14.7 kcal/mol about the amide (gamma') bond. A similar conformational theme was observed in the FAAF-12-mer duplex, d(CTTCTTG[FAAF]ACCTC).d(GAGGTCAAGAAG), which revealed two 19F resonances in a 41:59 ratio at 22 degrees C and pH 7.0. According to solvent-induced isotope and magnetic anisotropy effects, the two duplex conformers adopt exclusively a base displacement structure, being different only in their relative acetyl group orientations, cis (gamma' approximately 180 degrees) or trans (gamma' approximately 0 degrees ). Dynamic NMR data indicated that the two conformers do not exchange over a wide range of temperatures. This contrasts with the nonacetylated counterpart, which exhibits an equilibrium between the "B-type" and "stacked" conformers [Zhou, L., et al. (1997) J. Am. Chem. Soc. 119, 5384-5389]. The exclusive stacked nature of the AAF adducts may provide insight into why AAF adducts are more mutagenic and prone to repair than the nonacetylated AF adducts.
authors.affiliation: Department of Biomedical Sciences, College of Pharmacy, University of Rhode Island, Kingston 02881, USA. bcho@uri.edu
authors.forename: B P
authors.initials: BP
authors.lastname: Cho
authors.forename: L
authors.initials: L
authors.lastname: Zhou
mesh_terms: D015073:2-Acetylaminofluorene / Q000031:analogs & derivatives / Q000737:chemistry*; D002273:Carcinogens / Q000737:chemistry; D018736:DNA Adducts / Q000138:chemical synthesis / Q000737:chemistry*; D004277:DNA, Single-Stranded / Q000737:chemistry; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000737:chemistry*; D005449:Fluorenes / Q000737:chemistry; D005461:Fluorine; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D009690:Nucleic Acid Conformation; D012997:Solvents; D013816:Thermodynamics
chemical_list: D002273:Carcinogens; D018736:DNA Adducts; D004277:DNA, Single-Stranded; D005449:Fluorenes; D012997:Solvents; C031838:N-(deoxyguanosin-8-yl)-2-aminofluorene; D005461:Fluorine; C018776:N-(deoxyguanosin-8-yl)acetylaminofluorene; D015073:2-Acetylaminofluorene; D003849:Deoxyguanosine