Direct Measurement of 8OG Syn-Anti Flips in Mutagenic 8OG·A and Long-Range Damage-Dependent Hoogsteen Breathing Dynamics Using 1 H CEST NMR.

Elucidating how damage impacts DNA dynamics is essential for understanding the mechanisms of damage recognition and repair. Many DNA lesions alter their propensities to form low-populated and short-lived conformational states. However, NMR methods to measure these dynamics require isotopic enrichment, which is difficult for damaged nucleotides. Here, we demonstrate the utility of the 1 H chemical exchange saturation transfer (CEST) NMR experiment in measuring the dynamics of oxidatively damaged 8-oxoguanine (8OG) in the mutagenic 8OG syn ·A anti mismatch. Using 8OG-H7 as an NMR probe of the damaged base, we directly measured 8OG syn-anti flips to form a lowly populated (pop. ∼ 5%) and short-lived (lifetime ∼50 ms) nonmutagenic 8OG anti ·A anti . These exchange parameters were in quantitative agreement with values from 13 C off-resonance R 1ρ and CEST on the labeled partner adenine. The Watson-Crick-like 8OG syn ·A anti mismatch also rescued the kinetics of Hoogsteen motions at distant A-T base pairs, which the G·A mismatch had slowed down. The results lend further support for 8OG anti ·A anti as a minor conformational state of 8OG·A, reveal that 8OG damage can impact Hoogsteen dynamics at a distance, and demonstrate the utility of 1 H CEST for measuring damage-dependent dynamics in unlabeled DNA.