This research program seeks to delineate structure-activity relationships of DNA adducts that modulate frameshift vs. base substitution mutations, using NMR spectroscopy. Potential contributing factors include the covalent structure of adducts, their sequence context, and their ability to facilitate formation of transiently slipped structures during error-prone replication of the damaged DNA template. Effort focuses on three mutagens. Malondialdehyde (MDA), an endogenous mutagen arising from lipid peroxidation, induces both frameshifts and base pair substitutions, in a sequence-dependent manner. The principal adduct formed in human liver DNA by MDA is the pyrimidopurinone M1G, but in duplex DNA this rearranges to N2-(3-oxo-propenyl)-dG (OPG). The respective contributions of M1G and OPG to MDA mutagenesis are of considerable interest. M1G may be associated with base pair substitutions, while OPG may be responsible for frameshifts, perhaps by promoting transient strand slippage. OPG may also induce interstrand crosslinks. Aflatoxin B1 (AFB1), a mycotoxin, is a contaminant of human food. Epidemiological evidence suggests that it acts synergistically with the hepatitis B virus to promote hepatic tumors. AFB1 is an intercalating agent and thus might be presumed to be a frameshift mutagen, but this appears not to be the case. It is oxidized by cytochrome P450 to an epoxide, which reacts with DNA to form the cationic N7-dG alkylation product. Rearrangement of the cationic adduct forms the highly mutagenic formamidopyrimidine AFB1-FAPY. Its chemistry and structural biology in DNA remain poorly understood. New tandem LC-NMR methods may help elucidate its chemistry, which may differ in single-stand vs. duplex DNA. It stabilizes duplex DNA, and this may account for its mutagenicity, perhaps by decreasing repair efficiency, and perhaps by facilitating incorrect dNTP insertion during error-prone replication. It may also reduce transient strand slippage and hence frameshift mutagenesis. The heterocyclic arylamine IQ is formed during cooking. It induces both frameshifts and base pair substitutions; little is known about its structural biology in DNA. It forms both N2-dG and C8-dG adducts. The N2-dG adduct may induce less structural perturbation into DNA, be less efficiently repaired, and be responsible for base pair substitutions, whereas the C8-dG adduct may be associated with frameshifts.
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