Sensitivity enhancement in solution NMR through dynamic nuclear polarization

描述（由申请人提供）：蛋白质的结构和动力学方面一直处于我们理解其功能基础的中心阶段。溶液中的核磁共振对这一进步做出了重大贡献，NMR现象中固有的信息提供了更多。然而，尽管在技术、实验设计和分析策略方面取得了巨大的进步，但由于其非凡的不敏感性，溶液NMR光谱仍然受到根本性的限制。无法研究远低于亚毫摩尔浓度的蛋白质和其他生物聚合物，并使用亚微摩尔量，对未来的应用提出了严重的限制。然而，溶液NMR提供了，原则上，访问信息是非常难以获得的其他手段。例子包括访问动态在一个巨大的时间尺度范围内，配体结合的细节，结构在不寻常的context等，因此，它似乎是重要的，以提高溶液NMR实验的灵敏度，以减少实验时间，降低所需的样品的绝对量，并打开一个较低的浓度制度，其中有限的溶解度的蛋白质可以访问。考虑到这一点，一个“古老”的现象--动态核极化（DNP）--又复活了。这个想法是利用磁场中自由基电子的极强极化，使氢等原子核的极化程度比原子核本身性质所决定的玻尔兹曼分布大得多。这一过程的物理基础可能是相当复杂的，特别是在固态，其中几种极化机制是有效的。在溶液中，通常认为这种DNP转移将主要通过Overhauser效应发生。可以想象，灵敏度可以提高几百倍。对于溶液NMR，基本策略是使稳定自由基的电子跃迁饱和，并将这种非平衡极化转移到水的氢自旋，水的氢自旋又将这种极化转移到溶解的大分子的氢。不幸的是，这种方法的技术方面似乎证明对目前形式的想法是致命的。主要原因是合适的自由基的电子跃迁的频率位于subTHz光谱中，水强烈吸收。因此，辐照导致样品的灾难性加热及其破坏。这里 我们将利用溶解在具有合适介电特性的低粘度溶剂中的包封蛋白质溶液的物理性质。这些样本在很大程度上是透明的， 所需的subTHz频率，从而避免电子跃迁饱和期间的显著加热。从小到大的可溶性蛋白质、酸性蛋白质到碱性蛋白质、整合和锚定膜蛋白质、边缘稳定性蛋白质和核酸的各种蛋白质可以以高结构保真度被封装。因此，反胶束技术与DNP的合并将提供蛋白质和核酸的溶液NMR光谱的灵敏度的显著增加。

DESCRIPTION (provided by applicant): The structural and dynamic aspects of proteins have been at center stage of our understanding of the basis of their function. Nuclear magnetic resonance in solution has contributed significantly to this advancement and the information inherent in the NMR phenomena offers much more. Yet, despite tremendous advances in technology, experimental design and analytical strategies, solution NMR spectroscopy remains fundamentally restricted due to its extraordinary insensitivity. The inability to investigate protens and other biopolymers at well below sub-millimolar concentrations and using sub-micromole amounts presents severe limitations on future applications. Nevertheless, solution NMR offers, in principle, access to information that is very difficult to obtain by other means. Examples include access to dynamics over an enormous range of time scales, to details of ligand binding, to structures in unusual contexts and so on. Thus, it seems important to improve the sensitivity of the solution NMR experiment in order to reduce experiment time, lower the absolute quantities of sample required and open a lower concentration regime where proteins of limited solubility can be accessed. With this in mind there has been a revival of an "old" phenomenon - dynamic nuclear polarization (DNP). The idea is to use the enormously greater polarization of a radical electron in a magnetic field to polarize nuclei such as hydrogen to a much greater degree than the Boltzmann distribution dictated by the properties of the nuclei themselves. The physics underlying this process can be quite complicated, particularly in the solid state where several mechanisms for polarization are operative. In solution, it is generally thought that such DNP transfer will occur primarily through the Overhauser effect. One can imagine that increases in sensitivity of several hundred folds are accessible. For solution NMR, the basic strategy is to saturate the electronic transition of a stable free radical and transfer this non-equilibrium polarization to the hydrogen spins of water, which will in turn transfer this polarization to the hydrogens of the dissolved macromolecule. Unfortunately, technical aspects of this approach seem to prove fatal to the idea in its current form. The primary reason is that the frequency of the electron transition of suitable radicals lies in the subTHz spectrum where water absorbs strongly. Thus, irradiation results in catastrophic heating of the sample and its destruction. Here we will take advantage of the physical properties of solutions of encapsulated proteins dissolved in low viscosity solvents of suitable dielectric character. Such samples are largely transparent to the subTHz frequencies required and thereby avoid significant heating during saturation of the electronic transition. A variety of proteins ranging from small to large soluble proteins; acidic t basic proteins; integral and anchored membrane proteins; proteins of marginal stability and nucleic acids can be encapsulated with high structural fidelity. Thus the merging of the reverse micelle technology with DNP will provide a significant increase in the sensitivity of the solution NMR spectroscopy of proteins and nucleic acids.