Shingae Takahito, Kubota Kensuke, Kumauchi Masato, Tokunaga Fumio, Unno Masashi
†Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan.
‡Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, Oklahoma 74078, United States.
J Phys Chem Lett. 2013 Apr 18;4(8):1322-7. doi: 10.1021/jz400454j. Epub 2013 Apr 8.
Many biological cofactors, such as light-absorbing chromophores in photoreceptors, contain a π-electron system and are planar molecules. These cofactors are, however, usually nonplanar within a protein environment, and such structural distortions have been shown to be functionally important. Because the nonplanar structure makes the molecule chiral, Raman optical activity (ROA) provides a wealth of stereochemical information about the structural and conformational details of cofactors. The present study applied a near-infrared excited ROA to photoactive yellow protein, a blue light receptor. We successfully obtained the ROA spectra of the 4-hydroxycinnamyl chromophore embedded in a protein environment. Furthermore, calculations of the ROA spectra utilizing density functional theory provide detailed structural information, such as data on out-of-plane distortions of the chromophore. The structural information obtained from the ROA spectra includes the positions of hydrogen atoms, which are usually not detected in the crystal structures of biological samples.
许多生物辅因子，如光感受器中吸收光的发色团，都含有一个π电子系统，并且是平面分子。然而，这些辅因子在蛋白质环境中通常是非平面的，并且这种结构扭曲已被证明具有重要的功能。由于非平面结构使分子具有手性，拉曼光学活性（ROA）提供了大量有关辅因子结构和构象细节的立体化学信息。本研究将近红外激发的ROA应用于蓝光受体——光活性黄色蛋白。我们成功获得了嵌入蛋白质环境中的4-羟基肉桂基发色团的ROA光谱。此外，利用密度泛函理论对ROA光谱进行计算可提供详细的结构信息，如发色团平面外扭曲的数据。从ROA光谱获得的结构信息包括氢原子的位置，而这些位置在生物样品的晶体结构中通常是检测不到的。
