Gd3+ spin labeling for distance measurements by pulse EPR spectroscopy
Gd3+ spin labeling for distance measurements by pulse EPR spectroscopy
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DOI：
10.1039/c3cp53822b
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发表时间：
2014-01-01
影响因子：
3.3
通讯作者：
Goldfarb, Daniella
中科院分区：
文献类型：
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作者：
Goldfarb, Daniella
测量生物分子（蛋白质和核酸）及其复合物中特定位点之间纳米尺度距离的方法对于描述和分析其结构和功能至关重要。在过去的十年中，脉冲EPR技术被证明是非常有效的测量两个自旋标记之间的距离连接到一个生物分子。用于这种测量的最常用的自旋标记是氮氧稳定自由基。最近，一个新的家庭的自旋标签，Gd 3+螯合物的基础上，已被引入，以克服使用氮氧化物的一些限制，特别是在高磁场，这是有吸引力的，由于增加的灵敏度，他们提供。这样的S = 7/2自旋标记物为30 GHz和更高的频率，特别是在95 GHz下提供的益处包括（1）高灵敏度，仅需要类似于0.15 nmol的双标记生物分子，（2）缺乏取向选择，这允许直接的数据分析。Gd ~（3+）-Gd ~（3+）DEER（双电子-电子共振）距离测量在标记的肽、蛋白质和DNA上已经被证明，结果表明它们在灵敏度方面非常有前途。在这篇文章中，我们回顾了这些新的发展。简要介绍了S = 1/2自旋对的DEER实验的特点，并对Gd ~（3+）离子的EPR光谱性质进行了表征。然后，我们介绍了一些用于将Gd 3+连接到生物分子上的标签，并提供了Gd 3 +-Gd 3 + DEER测量的一些实验示例。其次是讨论影响这种DEER测量灵敏度的参数。由于Gd 3+自旋汉密尔顿中的一个重要项是零场分裂（ZFS），因此必须考虑它对DEER调制频率的影响，这将在下面讨论。最后，另一个最近报道的方法使用Gd 3+在距离测量将被提出：使用Gd 3 +-氮氧对。
Methods for measuring nanometer scale distances between specific sites in biomolecules (proteins and nucleic acids) and their complexes are essential for describing and analyzing their structure and function. In the last decade pulse EPR techniques were proven very effective for measuring distances between two spin labels attached to a biomolecule. The most commonly used spin labels for such measurements are nitroxide stable radicals. Recently, a new family of spin labels, based on Gd3+ chelates, has been introduced to overcome some of the limitations of using nitroxides, particularly at high magnetic fields, which are attractive due to the increased sensitivity they offer. The benefits that such S = 7/2 spin labels offer for frequencies of 30 GHz and higher, particularly at 95 GHz, include (1) high sensitivity, only similar to 0.15 nmol of doubly labeled biomolecule is needed, (2) the lack of orientation selection, which allows straightforward data analysis. Gd3+-Gd3+ DEER (double electron-electron resonance) distance measurements on labeled peptides, proteins and DNA have already been demonstrated and the results show that they are very promising in terms of sensitivity. In this Perspective we review these new developments. We briefly introduce the characteristics of the DEER experiment on a pair of S = 1/2 spins and characterize the EPR spectroscopic properties of Gd3+ ions. We then introduce some of the tags employed to attach Gd3+ to biomolecules and provide a few experimental examples of Gd3+-Gd3+ DEER measurements. This is followed by a discussion of the parameters that affect the sensitivity of such DEER measurements. Since an important term in the spin Hamiltonian of Gd3+ is the zero-field splitting (ZFS), its effect on the DEER modulation frequencies must be considered and this is discussed next. Finally, another recently reported approach for using Gd3+ in distance measurements will be presented: the use of Gd3+-nitroxide pairs.