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

We report a systematic spectroscopic investigation on the conformational evolution during primer extension of a bulky fluoroaminofluorene-modified 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 (19)F 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 pre-insertion 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 (T(m)) and thermodynamic (-ΔG°(37 °C)) stabilities were significantly reduced relative to those of the controls. However, the corresponding T(m) 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.