Hustedt Eric J, Stein Richard A, Sethaphong Latsavongsakda, Brandon Suzanne, Zhou Zheng, Desensi Susan C
Department of Molecular Physiology and Biophysics, and Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37232, USA.
Biophys J. 2006 Jan 1;90(1):340-56. doi: 10.1529/biophysj.105.068544. Epub 2005 Oct 7.
A tether-in-a-cone model is developed for the simulation of electron paramagnetic resonance spectra of dipolar coupled nitroxide spin labels attached to tethers statically disordered within cones of variable halfwidth. In this model, the nitroxides adopt a range of interprobe distances and orientations. The aim is to develop tools for determining both the distance distribution and the relative orientation of the labels from experimental spectra. Simulations demonstrate the sensitivity of electron paramagnetic resonance spectra to the orientation of the cones as a function of cone halfwidth and other parameters. For small cone halfwidths (< approximately 40 degrees ), simulated spectra are strongly dependent on the relative orientation of the cones. For larger cone halfwidths, spectra become independent of cone orientation. Tether-in-a-cone model simulations are analyzed using a convolution approach based on Fourier transforms. Spectra obtained by the Fourier convolution method more closely fit the tether-in-a-cone simulations as the halfwidth of the cone increases. The Fourier convolution method gives a reasonable estimate of the correct average distance, though the distance distribution obtained can be significantly distorted. Finally, the tether-in-a-cone model is successfully used to analyze experimental spectra from T4 lysozyme. These results demonstrate the utility of the model and highlight directions for further development.
开发了一种圆锥内系链模型，用于模拟偶极耦合的硝基氧自旋标记的电子顺磁共振光谱，这些自旋标记附着在半宽度可变的圆锥内静态无序的系链上。在该模型中，硝基氧采用一系列探针间距离和取向。目的是开发工具，以便从实验光谱确定标记的距离分布和相对取向。模拟表明电子顺磁共振光谱对圆锥取向的敏感性，该敏感性是圆锥半宽度和其他参数的函数。对于小的圆锥半宽度（<约40度），模拟光谱强烈依赖于圆锥的相对取向。对于较大的圆锥半宽度，光谱变得与圆锥取向无关。使用基于傅里叶变换的卷积方法分析圆锥内系链模型模拟。随着圆锥半宽度增加，通过傅里叶卷积方法获得的光谱更紧密地拟合圆锥内系链模拟。傅里叶卷积方法给出了正确平均距离的合理估计，尽管获得的距离分布可能会严重失真。最后，圆锥内系链模型成功用于分析来自T4溶菌酶的实验光谱。这些结果证明了该模型的实用性，并突出了进一步发展的方向。
