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Molecular distances from dipolar coupled spin-labels: the global analysis of multifrequency continuous wave electron paramagnetic resonance data.

机译:距偶极耦合自旋标记的分子距离:多频连续波电子顺磁共振数据的全局分析。

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摘要

For immobilized nitroxide spin-labels with a well-defined interprobe geometry, resolved dipolar splittings can be observed in continuous wave electron paramagnetic resonance (CW-EPR) spectra for interelectron distances as large as 30 A using perdeuterated probes. In this work, algorithms are developed for calculating CW-EPR spectra of immobilized, dipolar coupled nitroxides, and then used to define the limits of sensitivity to the interelectron distance as a function of geometry and microwave frequency. Secondly, the CW-EPR spectra of N epsilon-spin-labeled coenzyme NAD+ bound to microcrystalline, tetrameric glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have been collected at 9.8, 34, and 94 GHz. These data have been analyzed, using a combination of simulated annealing and global analysis, to obtain a unique fit to the data. The values of the intermitroxide distance and the five angles defining the relative orientation of the two nitroxides are in reasonable agreement with a molecular model built from the known crystal structure. Finally, the effect of rigid body isotropic rotational diffusion on the CW-EPR spectra of dipolar coupled nitroxides has been investigated using an algorithm based on Brownian dynamics trajectories. These calculations demonstrate the sensitivity of CW-EPR spectra to dipolar coupling in the presence of rigid body rotational diffusion.
机译:对于具有明确定义的探针几何结构的固定式一氧化氮自旋标记物,使用氘代探针可在连续波电子顺磁共振(CW-EPR)光谱中观察到最大30 A的电子间距离分辨出的偶极分裂。在这项工作中,开发了用于计算固定的,偶极耦合的氮氧化物的CW-EPR光谱的算法,然后将其定义为对电子间距离的敏感度极限,该极限是几何形状和微波频率的函数。其次,已在9.8、34和94 GHz处收集了与微晶四聚甘油醛-3-磷酸脱氢酶(GAPDH)结合的Nε旋转标记的辅酶NAD +的CW-EPR光谱。使用模拟退火和全局分析的组合对这些数据进行了分析,以获得与数据的唯一拟合。间氧化物距离和定义两个氮氧化物的相对取向的五个角度的值与由已知晶体结构建立的分子模型合理地吻合。最后,使用基于布朗动力学轨迹的算法研究了刚体各向同性旋转扩散对偶极耦合氮氧化物的CW-EPR谱的影响。这些计算证明了在刚性旋转扩散的情况下,CW-EPR谱对偶极耦合的敏感性。

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