Differing conformational pathways before and after chemistry for insertion of dATP vs. dCTP opposite 8-oxoG in DNA polymerase β

To elucidate how human DNA polymerase β (pol β) discriminates dATP from dCTP when processing 8-oxoguanine (8-oxoG), we analyze a series of dynamics simulations before and after the chemical step with dATP and dCTP opposite an 8-oxoG template started from partially open complexes of pol β. Analyses reveal that the thumb closing of pol β before chemistry is hampered when the incorrect nucleotide dATP is bound opposite 8-oxoG; the unfavorable interaction between active-site residue Tyr271 and dATP that causes an anti to syn change in the 8-oxoG (syn):dATP complex explains this slow motion, in contrast to the 8-oxoG (anti):dCTP system. Such differences in conformational pathways before chemistry for mismatched vs. matched complexes help explain the preference for correct insertion across 8-oxoG by pol β. Together with reference studies with an nonlesioned G template, we propose that 8-oxoG leads to lower efficiency in pol β’s incorporation of dCTP compared with G by affecting the requisite activesite geometry for the chemical reaction before chemistry. Furthermore, because the active site is far from ready for the chemical reaction following partial closing or even full thumb closing, we suggest that pol β is tightly controlled not only by the chemical step but also by a closely related requirement for subtle active-site rearrangements following thumb movement but prior to chemistry.