Measuring Nanometer Scale Distances by high-field Pulse Electron Paramagnetic Resonance Using Mn(II) Spin-Labels

测量纳米尺度距离的技术已经成为生物学中的宝贵工具，大分子构象动力学和相互作用如何决定细胞过程已经成为一个新的范式。脉冲电子双共振（PELDOR）光谱已被证明在这方面是非常有用的。该提案的主题是使用Mn（II）离子作为自旋标记的高微波频率（35至180 GHz）高磁场（高达6特斯拉）PELDOR的开发和应用。高场PELDOR主要有两个优点：（1）更小的样品体积（2 μL）和（2.）实现更高分辨率角度测量的潜力。为了实现这些好处，将需要新的光谱和化学方法。稳定的氮氧自由基是传统的9 GHz（0.3 T）PELDOR测量的自旋标记的选择，但它们远远不是最佳的使用在更高的磁场。相比之下，Mn（II）离子具有磁场依赖性，这使得它们作为高磁场PELDOR自旋标记物更具吸引力。虽然自旋为5/2的Mn（II）离子的EPR谱与S=1/2自由基的EPR谱一样明确，但它比自由基的EPR谱更复杂。因此，该项目的主要目标是了解这如何影响PELDOR测量，并开发解决甚至利用这种复杂性的方法。为了实现更大的效用，本项目的第二个主要目标是开发Mn（II）自旋标记技术，使Mn（II）PELDOR可以推广。最初，强大的Mn（II）双三联吡啶复合物将连接到模型系统和生物复合物使用类似的化学用于自由基。随着该技术的逐步完善，将探索其他复合物和连接化学。Mn（II）PELDOR将在“天然标记”的模型和生物系统（即天然结合Mn（II）离子的金属酶）以及使用将开发的技术合成标记的模型和生物系统上进行测试和研究。

Techniques for measuring nanometer-scale distances have become invaluable tools in biology, how large conformational dynamics and macromolecular interactions determine cellular process has become a new paradigm. Pulse electron double resonance (PELDOR) spectroscopy has proven to be extremely useful in this regard. The subject of this proposal is the development and application of high microwave-frequency (35 to 180 GHz) high-magnetic fields (up to 6 Tesla) PELDOR using Mn(II) ions as spin-labels. High-field PELDOR has principally two advantages: (1.) much smaller samples volumes (2 μL) and (2.) the potential for achieving higher resolution angle measurements. To realize these benefits, new spectroscopic and chemical approaches will be required. Stable nitroxide radicals are the spin-labels of choice for conventional 9 GHz (0.3 T) PELDOR measurements, but they are far from optimal for use at higher magnetic-fields. By contrast, Mn(II) ions have a magnetic-field dependence that makes them far more attractive as high magnetic-field PELDOR spin-labels. Although the EPR spectroscopy of spin-5/2 Mn(II) ions is as well-defined as S=1/2 radicals, it is more complex than that of radicals. Therefore, a major goal of this project is to understand how this affects PELDOR measurements and to develop approaches to address and even exploit this complexity. To achieve greater utility, the second major goal of this project is to develop Mn(II) spin-label technology so that Mn(II) PELDOR can be generalized. Initially, robust Mn(II) bis-terpyridine complexes will be attached to model systems and biological complexes using chemistry similar to that used for radicals. Other complexes and linking chemistries will be explored as the technique is progressively refined. The Mn(II) PELDOR will be tested on and used to study both model and biological systems that are “naturally labeled”, that is metalloenzymes that naturally bind Mn(II) ions, and those labeled synthetically using technology that will be developed.