Modeling Excluded Volume Effects for the Faithful Description of the Background Signal in Double Electron-Electron Resonance
Modeling Excluded Volume Effects for the Faithful Description of the Background Signal in Double Electron-Electron Resonance
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DOI：
10.1021/jp408338q
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发表时间：
2013-12-26
影响因子：
3.3
通讯作者：
Hinderberger, Dariush
中科院分区：
文献类型：
--
作者：
Kattnig, Daniel R.;Reichenwallner, Joerg;Hinderberger, Dariush
讨论了双电子-电子共振(DER)实验中背景信号的排除体积效应。假设漫射体是球对称的，基于壳因式分解方法，导出了背景信号的解析表达式。讨论了拥挤和偏心标签位置的影响。对于粒子中心的径向分布函数，使用Percus-Yevick近似来考虑拥挤。此外，还介绍了一种将粒子中心的对关联函数与偏心标记物的对关联函数联系起来的通用方法。导出了适用于短偶极演化时间和长偶极演化时间的极限表达式。此外，我们还指出了在什么情况下，具有显著排除量效应的背景类似于来自3到6个分维的背景。自旋探针人血清白蛋白(HSA)样品的鹿时域数据显示出排除量效应的强烈影响。排除的体积是通过同时分析在不同的蛋白质浓度下记录的光谱来确定的，但探针与蛋白质的比例是恒定的。使用自旋探针5-DOXYL-硬脂酸(5-DSA)和16-DOXYL-硬脂酸(16-DSA)，当它们被HSA捕获时，分别产生宽的和明确定义的距离分布。我们比较了分析这些数据的不同的、无模型的方法。最有希望的结果是所有光谱的同时Tikhonov正则化，当共同的背景模型被同时调整以使后验概率最大化时。对于HSA中的16-DSA样本，这是唯一允许抑制背景伪影的方法。我们认为，描述的同时分析过程可以普遍用于减少与从鹿谱中提取距离分布的病态提取相关的歧义。这种方法对于由宽距离分布产生的偶极信号特别有价值，因此，没有明显的偶极振荡。
We discuss excluded volume effects on the background signal of double electron-electron resonance (DEER) experiments. Assuming spherically symmetric pervaded volumes, an analytical expression of the background signal is derived based on the shell-factorization approach. The effects of crowding and off-center label positions are discussed. Crowding is taken into account using the Percus-Yevick approximation for the radial distribution function of the particle centers. In addition, a versatile approach relating the pair-correlation function of the particle centers with those of off-center labels is introduced. Limiting expressions applying to short and long dipolar evolution times are derived. Furthermore, we show under which conditions the background with significant excluded volume effects resembles that originating from a fractal dimensionality ranging from 3 to 6. DEER time domain data of spin-probed samples of human serum albumin (HSA) are shown to be strongly affected by excluded-volume effects. The excluded volume is determined from the simultaneous analysis of spectra recorded at various protein concentrations but a constant probe-to-protein ratio. The spin-probes 5-DOXYL-stearic acid (5-DSA) and 16-DOXYL-stearic acid (16-DSA) are used, which, when taken up by HSA, give rise to broad and well-defined distance distributions, respectively. We compare different, model-free approaches of analyzing these data. The most promising results are obtained by the concurrent Tikhonov regularization of all spectra when a common background model is simultaneously adjusted such that the a posteriori probability is maximized. For the samples of 16-DSA in HSA, this is the only approach that allows suppressing a background artifact. We suggest that the delineated simultaneous analysis procedure can be generally applied to reduce ambiguities related to the ill-posed extraction of distance distributions from DEER spectra. This approach is particularly valuable for dipolar signals resulting from broad distance distributions, which as a consequence, are devoid of explicit dipolar oscillations.