Department of Chemistry, Graduate School of Science , Osaka University , 1-1 Machikaneyama , Toyonaka , Osaka 560-0043 , Japan.
Department of Life Science and Applied Chemistry , Nagoya Institute of Technology , Showa-ku, Nagoya , Aichi 466-8555 , Japan.
J Phys Chem B. 2019 Apr 25;123(16):3430-3440. doi: 10.1021/acs.jpcb.9b00928. Epub 2019 Apr 16.
We conducted a comprehensive time-resolved resonance Raman spectroscopy study of the structures of the retinal chromophore during the photocycle of the sodium-ion pump Krokinobacter rhodopsin 2 (KR2). We succeeded in determining the structure of the chromophore in the unphotolyzed state and in the K, L, M, and O intermediates, by overcoming the problem that only a small fraction of the M intermediate is accumulated in the KR2 photocycle. The Schiff base in the retinal chromophore forms a strong hydrogen bond in the unphotolyzed state and in the K, L, and O intermediates and is deprotonated in the M intermediate. Formation of this strong hydrogen bond facilitates deprotonation of the Schiff base, which is necessary for the sodium ion to move past the Schiff base. The polyene chain in the chromophore of KR2 is twisted in all of the states of the photocycle: the portion near the Schiff base is largely twisted in the unphotolyzed state and in the K intermediate, whereas the middle portion of the polyene chain becomes largely twisted in the L, M, and O intermediates. During the photocycle, the twisted structure of the polyene chain and strong hydrogen bond at the Schiff base are advantageous for transient relocation of the Schiff base proton. The obtained resonance Raman data clarified the unique structural features of the KR2 chromophore, which are not accessible by other methods.
我们对钠离子泵视紫红质 2（KR2）的光循环过程中视黄醛发色团的结构进行了全面的时间分辨共振拉曼光谱研究。通过克服仅在 KR2 光循环中积累少量 M 中间态的问题，我们成功地确定了未光解态和 K、L、M 和 O 中间态中发色团的结构。视黄醛发色团中的席夫碱在未光解态和 K、L 和 O 中间态中形成强氢键，并在 M 中间态中去质子化。这种强氢键的形成促进了席夫碱的去质子化，这对于钠离子通过席夫碱移动是必要的。在光循环的所有状态下，KR2 发色团中的聚烯链都扭曲：在未光解态和 K 中间态中，靠近席夫碱的部分大部分扭曲，而聚烯链的中间部分在 L、M 和 O 中间态中变得大部分扭曲。在光循环过程中，聚烯链的扭曲结构和席夫碱上的强氢键有利于席夫碱质子的瞬时重定位。获得的共振拉曼数据阐明了 KR2 发色团的独特结构特征，这是其他方法无法获得的。
