NMR study of stacking interactions and conformational adjustment in the dinucleotide-carcinogen adduct 2'-deoxycytidylyl-(3. -->. 5)-2'deoxy-8-(N-flouren-2-ylacetamido)guanosine

Journal Article · Tue Apr 19 00:00:00 EDT 1988 · Biochemistry; (United States)

OSTI ID:7225145

Evans, F E; Levine, R A

The conformation and dynamics of the dinucleotide d-CpG modified at the C(8) position of the guanine ring by the carcinogen 2-(acetylamino)fluorene has been investigated by high-field /sup 1/H NMR spectroscopy. A two-state analysis of chemical shift data has enabled estimation of the extent of intramolecular stacking in aqueous solution as a function of temperature. The stacking, which is mostly fluorene-cytosine, is virtually complete in the low-temperature range. The 500-MHz /sup 1/H NMR spectrum consists of two subspectra near ambient temperatures due to a 14.3 +/- 0.3 kcal/mol barrier to internal rotation about the amide bond in the stacked form. Problems of self-association and chemical exchange were identified and overcome to enable analysis of the sugar-phosphate backbone conformation utilizing coupling constants. For the exocyclic C(4')-C(5') bond of the deoxyguanosine moiety, there is a high gauche/sup +/ conformer population, which is uncommon for a purine nucleotide with a syn orientation about the glycosyl bond. The gauche/sup -/ conformation, which is normally present in syn purine nucleotides in solution, was not detected. The exocyclic C(5')-O(5') torsion of the deoxyguanosine moiety remains near the classical energy minimum in the major stacked conformations. The sugar ring of the deoxycytidine moiety is predominantly in the C2'-endo conformation, while the deoxyguanosine ring is a mixture of conformations, one of which appears to be unusually puckered. The results support intercalation models of modified DNA and suggest a looped-out structure, with the modified guanine being the first base in the loop. Such structures could explain the relatively rapid rate of repair and the frame-shift mutations of this type of adduct.

• Research Organization: National Center for Toxicological Research, Jefferson, AR (USA)
• OSTI ID: 7225145
• Journal Information: Biochemistry; (United States), Vol. 27:8
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
59 BASIC BIOLOGICAL SCIENCES
FLUORENE
DNA ADDUCTS
NUCLEAR MAGNETIC RESONANCE
OLIGONUCLEOTIDES
CONFORMATIONAL CHANGES
AQUEOUS SOLUTIONS
CHEMICAL SHIFT
CONDENSED AROMATICS
DNA REPAIR
GENE MUTATIONS
HYDROCARBONS
PROTONS
TEMPERATURE EFFECTS
ADDUCTS
AROMATICS
BARYONS
BIOLOGICAL RECOVERY
BIOLOGICAL REPAIR
DISPERSIONS
ELEMENTARY PARTICLES
FERMIONS
HADRONS
MAGNETIC RESONANCE
MIXTURES
MUTATIONS
NUCLEIC ACIDS
NUCLEONS
ORGANIC COMPOUNDS
RECOVERY
REPAIR
RESONANCE
SOLUTIONS
560300* - Chemicals Metabolism & Toxicology
550501 - Metabolism- Tracer Techniques