Accessibility of nitroxide side chains: Absolute Heisenberg exchange rates from power saturation EPR
Accessibility of nitroxide side chains: Absolute Heisenberg exchange rates from power saturation EPR
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DOI：
10.1529/biophysj.105.059063
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发表时间：
2005-09-01
影响因子：
3.4
通讯作者：
Hubbell, WL
中科院分区：
文献类型：
--
作者：
Altenbach, C;Froncisz, W;Hubbell, WL
在定点自旋标记中，自旋标记侧链的相对溶剂可及性与溶液中氮氧化合物与顺磁试剂的海森堡交换速率（W-ex）成比例。反过来，W-ex的相对值由连续波功率饱和方法确定，并表示为比例和无量纲参数Pi。在这里提出的实验中，NiEDDA的特点是作为一种顺磁性试剂的溶剂可及性的研究，它表明，W-ex的绝对值可以确定从Pi，与它们相关的比例常数是独立的顺磁性试剂和流动性的氮氧化物。基于绝对交换率，定义可及性因子（0 < rho < 1），其用作侧链溶剂可及性的定量量度。T4溶菌酶中14个不同位点处氮氧侧链的可及性因子与源自蛋白质晶体结构的基于结构的可及性参数相关。这些结果提供了一个有用的手段，有关晶体学和定点自旋标记数据，从而比较晶体和溶液结构。
In site-directed spin labeling, the relative solvent accessibility of spin-labeled side chains is taken to be proportional to the Heisenberg exchange rate (W-ex) of the nitroxide with a paramagnetic reagent in solution. In turn, relative values of W-ex are determined by continuous wave power saturation methods and expressed as a proportional and dimensionless parameter Pi. In the experiments presented here, NiEDDA is characterized as a paramagnetic reagent for solvent accessibility studies, and it is shown that absolute values of W-ex can be determined from Pi, and that the proportionality constant relating them is independent of the paramagnetic reagent and mobility of the nitroxide. Based on absolute exchange rates, an accessibility factor is defined (0 < rho < 1) that serves as a quantitative measure of side-chain solvent accessibility. The accessibility factors for a nitroxide side chain at 14 different sites in T4 lysozyme are shown to correlate with a structure-based accessibility parameter derived from the crystal structure of the protein. These results provide a useful means for relating crystallographic and site-directed spin labeling data, and hence comparing crystal and solution structures.