NMR sensitivity-enhancement methods involving hyperpolarized water could be of importance for solution-state biophysical investigations. Hyperpolarized water (HyperW) can enhance the 1H NMR signals of exchangeable sites by orders of magnitude over their thermal counterparts, while providing insight into chemical exchange and solvent accessibility at a site-resolved level. As HyperW's enhancements are achieved by exploiting fast solvent exchanges associated with minimal interscan delays, possibilities for the rapid monitoring of chemical reactions and biomolecular (re)folding are opened. HyperW NMR can also accommodate heteronuclear transfers, facilitating the rapid acquisition of 2-dimensional (2D) 15N-1H NMR correlations, and thereby combining an enhanced spectral resolution with speed and sensitivity. This work demonstrates how these qualities can come together for the study of nucleic acids. HyperW injections were used to target the guanine-sensing riboswitch aptamer domain (GSRapt) of the xpt-pbuX operon in Bacillus subtilis Unlike what had been observed in proteins, where residues benefited of HyperW NMR only if/when sufficiently exposed to water, these enhancements applied to every imino resonance throughout the RNA. The >300-fold enhancements observed in the resulting 1H NMR spectra allowed us to monitor in real time the changes that GSRapt undergoes upon binding hypoxanthine, a high-affinity interaction leading to conformational refolding on a ∼1-s timescale at 36 °C. Structural responses could be identified for several nucleotides by 1-dimensional (1D) imino 1H NMR as well as by 2D HyperW NMR spectra acquired upon simultaneous injection of hyperpolarized water and hypoxanthine. The folding landscape revealed by this HyperW strategy for GSRapt, is briefly discussed.

中文翻译：

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超极化水使亚氨基核酸共振增强300倍，为通过1D和2D NMR探测RNA重折叠提供了新的窗口。

涉及超极化水的NMR灵敏度增强方法对于溶液状态生物物理研究可能非常重要。超极化水（HyperW）可以将可交换位点的1H NMR信号增强到比其热对应物高几个数量级，同时在位点分辨的水平上洞悉化学交换和溶剂的可及性。随着HyperW的增强通过利用与最小扫描间延迟相关的快速溶剂交换来实现，因此打开了快速监控化学反应和生物分子（重新）折叠的可能性。HyperW NMR还可以适应异核转移，有助于快速获取二维（2D）15N-1H NMR相关性，从而将增强的光谱分辨率与速度和灵敏度结合在一起。这项工作演示了如何将这些质量结合起来用于核酸研究。HyperW注射用于靶向枯草芽孢杆菌中xpt-pbuX操纵子的鸟嘌呤敏感核糖开关适体结构域（GSRapt），与蛋白质中观察到的不同，只有当/充分暴露于水时，残留物才能从HyperW NMR中受益。应用于整个RNA的每个亚氨基共振。在所得1H NMR谱图中观察到的> 300倍的增强使我们能够实时监测GSRapt在结合次黄嘌呤后经历的变化，这种高亲和力相互作用导致构象在36°C时重新折叠。通过一维（1D）亚氨基1H NMR以及通过同时注射超极化水和次黄嘌呤获得的2D HyperW NMR光谱，可以鉴定出几个核苷酸的结构响应。简要讨论了此HyperW GSRapt策略所揭示的折叠格局。