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Lipid-gramicidin interactions using two-dimensional Fourier-transform electron spin resonance.

机译:使用二维傅立叶变换电子自旋共振的脂质-大蒜素相互作用。

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摘要

The application of two-dimensional Fourier-transform electron-spin-resonance (2D-FT-ESR) to the study of lipid/gramicidin A (GA) interactions is reported. It is shown that 2D-FT-ESR spectra provide substantially enhanced spectral resolution to changes in the dynamics and ordering of the bulk lipids (as compared with cw-ESR spectra), that result from addition of GA to membrane vesicles of dipalmitoylphosphatidylcholine (DPPC) in excess water containing 16-PC as the lipid spin label. The agreement between the theory of Lee, Budil, and Freed and experimental results is very good in the liquid crystalline phase. Both the rotational and translational diffusion rates of the bulk lipid are substantially decreased by addition of GA, whereas the ordering is only slightly increased, for a 1:5 ratio of GA to lipid. The slowing effect on the diffusive rates of adding GA in the gel phase is less pronounced. It is suggested that the spectral fits in this phase would be improved with a more detailed dynamic model. No significant evidence is found in the 2D-FT-ESR spectra for a second immobilized component upon addition of GA, which is in contrast to cw-ESR. It is shown from simulations of the observed 2D-FT-ESR spectra that the additional component seen in cw-ESR spectra, and usually attributed to "immobilized" lipid, is inconsistent with its being characterized by increased ordering, according to a model proposed by Ge and Freed, but it would be consistent with the more conventional model of a significantly reduced diffusional rate. This is because the 2D-FT-ESR spectra exhibit a selectivity, favoring components with longer homogeneous relaxation times, T2. The homogeneous linewidths of the 2D-FT-ESR autopeaks appear to broaden as a function of mixing time. This apparent broadening is very likely due to the process of cooperative order director fluctuations (ODF) of the lipids in the vesicle. This real-time observation of ODF is distinct from, but appears in reasonable agreement with, NMR results. It is found that addition of GA to give the 1:5 ratio has only a small effect on the ODF, but there is a significant temperature dependence.
机译:报道了二维傅里叶变换电子自旋共振(2D-FT-ESR)在脂质/大蒜素A(GA)相互作用研究中的应用。结果表明2D-FT-ESR光谱提供了显着增强的光谱分辨率,以改变脂质的动力学和有序性(与cw-ESR光谱相比),这是由于将GA添加到二棕榈酰磷脂酰胆碱(DPPC)的膜囊泡中所致在含有16-PC作为脂质旋转标记的过量水中。 Lee,Budil和Freed的理论与实验结果在液晶相中的一致性很好。通过添加GA,大量脂质的旋转扩散和翻译扩散速率均显着降低,而对于GA与脂质的比例为1:5,顺序仅略有增加。在凝胶相中添加GA的扩散速率的减慢效果不太明显。建议使用更详细的动态模型来改善此阶段的光谱拟合。在2D-FT-ESR光谱中未发现添加GA后第二种固定化组分的明显证据,这与cw-ESR相反。根据观察到的2D-FT-ESR光谱的模拟显示,在cw-ESR光谱中看到的通常归因于“固定化”脂质的其他成分与以增加的有序性为特征的不一致,根据由Ge和Freed,但与扩散速率显着降低的更常规模型相一致。这是因为2D-FT-ESR光谱表现出选择性,有利于具有更长的均匀弛豫时间T2的组分。 2D-FT-ESR自动峰的均匀线宽似乎随着混合时间而变宽。这种明显的增宽很可能归因于囊泡中脂质的合作顺序指导者起伏(ODF)。 ODF的这种实时观测不同于NMR结果,但与NMR结果有合理的一致性。发现以1:5的比例添加GA对ODF仅具有很小的影响,但是具有显着的温度依赖性。

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