Gast P, Herbonnet R T L, Klare J, Nalepa A, Rickert C, Stellinga D, Urban L, Möbius K, Savitsky A, Steinhoff H-J, Groenen E J J
Huygens-Kamerlingh Onnes Laboratory, Department of Physics, Leiden University, P.O. Box 9504, NL-2300 RA Leiden, The Netherlands.
Phys Chem Chem Phys. 2014 Aug 14;16(30):15910-6. doi: 10.1039/c4cp01741b.
On the basis of experiments at 275 GHz, we reconsider the dependence of the continuous-wave EPR spectra of nitroxide spin-labeled protein sites in sensory- and bacteriorhodopsin on the micro-environment. The high magnetic field provides the resolution necessary to disentangle the effects of hydrogen bonding and polarity. In the gxx region of the 275 GHz EPR spectrum, bands are resolved that derive from spin-label populations carrying no, one or two hydrogen bonds. The gxx value of each population varies hardly from site to site, significantly less than deduced previously from studies at lower microwave frequencies. The fractions of the populations vary strongly, which provides a consistent description of the variation of the average gxx and the average nitrogen-hyperfine interaction Azz from site to site. These variations reflect the difference in the proticity of the micro-environment, and differences in polarity contribute marginally. Concomitant W-band ELDOR-detected NMR experiments on the corresponding nitroxide in perdeuterated water resolve population-specific nitrogen-hyperfine bands, which underlies the interpretation for the proteins.
基于在275吉赫兹的实验，我们重新审视了感官视紫红质和细菌视紫红质中氮氧自旋标记蛋白位点的连续波电子顺磁共振（EPR）光谱对微环境的依赖性。高磁场提供了分辨氢键和极性效应所需的分辨率。在275吉赫兹EPR光谱的gxx区域，分辨出了来自不带氢键、带一个或两个氢键的自旋标记群体的谱带。每个群体的gxx值在不同位点之间变化很小，明显小于先前在较低微波频率研究中推断的值。群体的比例变化很大，这为不同位点之间平均gxx和平均氮超精细相互作用Azz的变化提供了一致的描述。这些变化反映了微环境质子性的差异，而极性差异的贡献很小。在重水对相应氮氧进行的伴随W波段电子双共振检测核磁共振实验分辨出了群体特异性的氮超精细谱带，这是对蛋白质进行解释的基础。
