Molecular Dynamics Simulations of Mismatched DNA Duplexes Associated with the Major C8-Linked 2'-Deoxyguanosine Adduct of the Food Mutagen Ochratoxin A: Influence of Opposing Base, Adduct Ionization State, and Sequence on the Structure of Damaged DNA.

Abstract

Exposure to ochratoxin A (OTA) is associated with chronic renal diseases and carcinogenesis. The deleterious effects of OTA have been linked to its covalent binding at the C8 position of guanine (G) to form a DNA adduct (OT-G), which causes various mutations. To contribute toward understanding the complex mutagenic profile of OTA, the present work uses a robust computational approach to characterize postreplication DNA structures containing OT-G mismatched with canonical nucleobases. Our MD simulations provide insight into the effects of the opposing base, adduct ionization state, and flanking base on duplex structural features for the competing (major groove (B-type), wedge (W), and stacked (S)) conformers. For the B-type duplexes, our data suggest that significantly more stable lesion-site hydrogen bonding may lead to preferential insertion of an opposing cytosine (C) if the OT moiety is directed toward the major groove at the replication fork. Although the W conformation is consistently predicted to be less stable than the B conformer, a G mismatch is likely the most stable and least distorted replication outcome when the bulky moiety is directed into the DNA minor groove. These findings directly correlate with the limited contribution of substitution mutations to the overall mutagenic profile of OTA and suggest that the dominant mutations are G → C transversions. In contrast, stable S conformers that are known precursors to small (one- or two-base) deletion mutations are found when the lesion is opposite cytosine, adenine, or thymine, which directly correlates with the large number of deletion mutations previously reported for animals exposed to OTA. Nevertheless, the predicted sequence and ionization-dependent distortion of the S conformer points toward the dependence of the repair propensity on the cellular environment, which rationalizes the reported tissue specific OTA-induced toxicity.