Chiang Yun-Wei, Borbat Peter P, Freed Jack H
Baker Laboratory of Chemistry and Chemical Biology, National Biomedical ACERT Center for Advanced ESR Technology, Cornell University, Ithaca, NY 14853-1301, USA.
J Magn Reson. 2005 Feb;172(2):279-95. doi: 10.1016/j.jmr.2004.10.012.
Pulsed ESR techniques with the aid of site-directed spin labeling have proven useful in providing unique structural information about proteins. The determination of distance distributions in electron spin pairs directly from the dipolar time evolution of the pulsed ESR signals by means of the Tikhonov regularization method is reported. The difficulties connected with numerically inverting this ill-posed mathematical problem are clearly illustrated. The Tikhonov regularization with the regularization parameter determined by the L-curve criterion is then described and tested to confirm its accuracy and reliability. The method is applied to recent experimental results on doubly labeled proteins that have been studied using two pulsed ESR techniques, double quantum coherence (DQC) ESR and double electron-electron resonance (DEER). The extracted distance distributions are able to provide valuable information about the conformational constraints in various partially folded states of proteins. This study supplies a mathematically reliable method for extracting pair distributions from pulsed ESR experimental data and has extended the use of pulsed ESR to provide results of greater value for structural biology.
借助定点自旋标记的脉冲电子自旋共振（ESR）技术已被证明有助于提供有关蛋白质的独特结构信息。本文报道了通过蒂霍诺夫正则化方法直接从脉冲ESR信号的偶极时间演化确定电子自旋对中的距离分布。文中清晰地阐述了数值求解这个不适定数学问题所面临的困难。接着描述并测试了通过L曲线准则确定正则化参数的蒂霍诺夫正则化方法，以确认其准确性和可靠性。该方法应用于近期使用双量子相干（DQC）ESR和双电子 - 电子共振（DEER）这两种脉冲ESR技术研究的双标记蛋白质的实验结果。提取的距离分布能够提供有关蛋白质各种部分折叠状态下构象限制的有价值信息。这项研究提供了一种从脉冲ESR实验数据中提取对分布的数学可靠方法，并扩展了脉冲ESR的应用，为结构生物学提供了更有价值的结果。
