NMR off-resonance R_1ρ relaxation dispersion measurements on base carbon and nitrogen nuclei have revealed that wobble G·T/U mismatches in DNA and RNA duplexes exist in dynamic equilibrium with short-lived, low-abundance, and mutagenic Watson–Crick-like conformations. As Watson–Crick-like G·T mismatches have base pairing geometries similar to Watson–Crick base pairs, we hypothesized that they would mimic Watson–Crick base pairs with respect to the sugar-backbone conformation as well. Using off-resonance R_1ρ measurements targeting the sugar C3′ and C4′ nuclei, a structure survey, and molecular dynamics simulations, we show that wobble G·T mismatches adopt sugar-backbone conformations that deviate from the canonical Watson–Crick conformation and that transitions toward tautomeric and anionic Watson–Crick-like G·T mismatches restore the canonical Watson–Crick sugar-backbone. These measurements also reveal kinetic isotope effects for tautomerization in D₂O versus H₂O, which provide experimental evidence in support of a transition state involving proton transfer. The results provide additional evidence in support of mutagenic Watson–Crick-like G·T mismatches, help rule out alternative inverted wobble conformations in the case of anionic G·T⁻, and also establish sugar carbons as new non-exchangeable probes of this exchange process.

对基础碳和氮核的NMR 偏共振R _1ρ弛豫色散测量表明，DNA 和 RNA 双链体中的摆动 G·T/U 错配存在于动态平衡中，具有短暂、低丰度和诱变的 Watson-Crick 样构象。由于 Watson-Crick 样 G·T 错配具有与 Watson-Crick 碱基对相似的碱基配对几何结构，我们假设它们在糖骨架构象方面也会模仿 Watson-Crick 碱基对。使用偏共振R _1ρ针对糖 C3' 和 C4' 核的测量、结构调查和分子动力学模拟，我们表明摆动 G·T 错配采用偏离典型 Watson-Crick 构象的糖骨架构象，并转变为互变异构和阴离子 Watson – 类似克里克的 G·T 不匹配恢复了典型的沃森–克里克糖主干。这些测量还揭示了 D ₂ O 与 H ₂ O 中互变异构化的动力学同位素效应，这为支持涉及质子转移的过渡态提供了实验证据。结果提供了额外的证据来支持诱变的 Watson-Crick 样 G·T 不匹配，有助于排除阴离子 G·T 情况下的替代倒摆动构象^-，并建立糖碳作为这种交换过程的新的不可交换的探针。