Structural features of DNA polymerases β and λ in complex with benzo[a]pyrene-adducted DNA cause a difference in lesion tolerance.

DNA polymerases β (Pol β) and λ (Pol λ) belong to one structural family (X family) and possess the same enzymatic activities. Nonetheless, these enzymes have differences in their catalytic efficiency and specificity. We have previously reported that these enzymes can bypass bulky benzo[a]pyrene-DNA adducts via translesion synthesis during gap-filling reactions, although efficiency and specificity are dependent on the reaction conditions and adduct conformation. In the present study, we analyzed structural features of Pols β and λ complexed with a gapped DNA duplex containing either cis- or trans-benzo[a]pyrene-diol epoxide-N-dG (BP-dG) using molecular dynamics simulations. It was found that the most pronounced structural difference lies in the positioning of the trans-BP-dG residue relative to secondary structures of the protein; this dissimilarity may explain the differences between Pols β and λ in gap-filling/translesion synthesis. In the case of Pol β, trans-BP-dG turned out to be positioned parallel to the α-helix and β-sheet. In the Pol λ complex, trans-BP-dG is perpendicular to the α-helix. This difference persisted throughout the molecular dynamics trajectory. Selectivity for the BP-dG isomers remained after a deletion of noncatalytic domains of Pol λ. Modeling of Pol λ or β complexes with cis-BP-dG-containing DNA in the presence of Mn either at both metal-binding sites or at the catalytic site only revealed that for both enzymes, the model of the complex containing both Mg and Mn is stabler than that containing two Mn ions. This observation may reflect a shared property of these enzymes: the preference for Mn in terms of catalysis and for Mg regarding triphosphate coordination during the translesion reaction.