Conformational and thermodynamic impact of bulky aminofluorene adduction on simulated translesion DNA synthesis

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We report a systematic spectroscopic investigation on the conformational evolution during primer extension of a bulky fluoroaminoflurene-modfied dG adduct (FAF-dG) in chemically simulated translesion synthesis. FAF-dG was paired either with dC or dA (dC-match and dA-mismatch series, respectively). Dynamic 19F NMR/CD results showed that the FAF-adduct exists in a syn/anti equilibrium and that its conformational characteristics are modulated by the identity of an inserted nucleotide at the lesion site and the extent of primer elongation. At the preinsertion site, the adduct adopted preferentially a syn conformation where FAF stacked with preceding bases. Insertion of the correct nucleotide dC at the lesion site and subsequent elongation resulted in a gradual transition to the anti conformation. By contrast, the syn conformer was persistent along with primer extension in the dA-mismatch series. In the dC-match series, FAF-induced thermal (Tm) and thermodynamic (-ΔG°37 °C) stabilities were significantly reduced relative to those of the controls. However, the corresponding Tm and -ΔG°37 °C values were increased in the FAF-modified mismatched dA series. The lesion impact persisted up to three 5′-nucleotides from the lesion. Occupation of the minor groove of the W-conformer with the bulky carcinogenic fluorene moiety not only would limit the DNA mobility but also would impose a serious difficulty for the active site of a polymerase throughout the replication process. Our spectroscopic results are consistent with reported data on AF, which showed dramatic (∼10 4-fold) differences in the nucleotide insertion rates between the dC-match and dA-mismatch series. The results emphasize the importance of adduct-induced steric constraints for determining the replication fidelity of a polymerase. © 2011 American Chemical Society.

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Chemical Research in Toxicology