Li Siyu, Yang Hanming, Hofstetter Heike, Tonelli Marco, Cavagnero Silvia
Department of Chemistry, University of Wisconsin - Madison, 1101 University Ave., Madison, Wisconsin, 53706, USA.
Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, Wisconsin, 53706, USA.
Appl Magn Reson. 2023 Jan;54(1):59-75. doi: 10.1007/s00723-022-01506-7. Epub 2022 Oct 15.
NMR spectroscopy is well known for its superb resolution, especially at high applied magnetic field. However, the sensitivity of this technique is very low. Liquid-state low-concentration photo-chemically-induced dynamic nuclear polarization (LC-photo-CIDNP) is a promising emerging methodology capable of enhancing NMR sensitivity in solution. LC-photo-CIDNP works well on solvent-exposed Trp and Tyr residues, either in isolation or within proteins. This study explores the magnetic-field dependence of the LC-photo-CIDNP experienced by two tryptophan isotopologs in solution upon LED-mediated optical irradiation. Out of the two uniformly C,N-labeled Trp (Trp-U-C,N) and Trp-α-C-β,β,2,4,5,6,7-d species employed here, only the latter bears a quasi-isolated H-C spin pair. Computer simulations of the predicted polarization due to geminate recombination of both species display a roughly bell-shaped field dependence. However, while Trp-U-C,N is predicted to show a maximum at ca. 500 MHz (11.7 T) and a fairly weak field dependence, Trp-α-C-β,β,2,4,5,6,7-d is expected to display a much sharper field dependence accompanied by a dramatic polarization increase at lower field (ca. 200 MHz, 4.7 T). Experimental LC-photo-CIDNP studies on both Trp isotopologs at 1μM concentration, performed at selected fields, are consistent with the theoretical predictions. In summary, this study highlights the prominent field-dependence of LC-photo-CIDNP enhancements () experienced by Trp isotopologs bearing a quasi-isolated spin pair.
核磁共振光谱以其卓越的分辨率而闻名，尤其是在高外加磁场下。然而，该技术的灵敏度非常低。液态低浓度光化学诱导动态核极化（LC-光CIDNP）是一种有前途的新兴方法，能够提高溶液中的核磁共振灵敏度。LC-光CIDNP在暴露于溶剂的色氨酸（Trp）和酪氨酸（Tyr）残基上效果良好，无论是孤立的还是在蛋白质内部。本研究探讨了溶液中两种色氨酸同位素异构体在LED介导的光照射下所经历的LC-光CIDNP的磁场依赖性。在这里使用的两种均匀C、N标记的Trp（Trp-U-C,N）和Trp-α-C-β,β,2,4,5,6,7-d物种中，只有后者带有准孤立的H-C自旋对。对这两种物种由于双分子复合而产生的预测极化的计算机模拟显示出大致呈钟形的磁场依赖性。然而，虽然预计Trp-U-C,N在约500 MHz（11.7 T）处显示最大值且磁场依赖性相当弱，但Trp-α-C-β,β,2,4,5,6,7-d预计将显示出更尖锐的磁场依赖性，并在较低场（约200 MHz，4.7 T）下伴随着极化的急剧增加。在选定磁场下对两种1μM浓度的Trp同位素异构体进行的实验LC-光CIDNP研究与理论预测一致。总之，本研究突出了带有准孤立自旋对的Trp同位素异构体所经历的LC-光CIDNP增强的显著磁场依赖性。
