Mizuno Misao, Nakajima Ayumi, Kandori Hideki, Mizutani Yasuhisa
Department of Chemistry, Graduate School of Science , Osaka University , 1-1 Machikaneyama , Toyonaka , Osaka 560-0043 , Japan , and.
Department of Frontier Materials , Nagoya Institute of Technology , Showa-ku, Nagoya , Aichi 466-8555 , Japan.
J Phys Chem A. 2018 Mar 8;122(9):2411-2423. doi: 10.1021/acs.jpca.7b12332. Epub 2018 Feb 26.
We revealed the chloride ion pumping mechanism in halorhodopsin from Natronobacterium pharaonis ( pHR) by exploring sequential structural changes in the retinal chromophore during its photocycle using time-resolved resonance Raman (RR) spectroscopy on the nanosecond to millisecond time scales. A series of RR spectra of the retinal chromophore in the unphotolyzed state and of the three intermediates of pHR were obtained. Using singular value decomposition analysis of the C═C and C-C stretch bands in the time-resolved RR spectra, we identified the spectra of the K, L, and N intermediates. We focused on structural markers of the RR bands to explore the structure of the retinal chromophore. In the unphotolyzed state, the retinal chromophore is in the planar all- trans, 15- anti geometry. The bound ion affects the polyene chain but does not interact with the protonated Schiff base. In the observed intermediates, the chromophore is in the 13- cis configuration. The chromophore in the K intermediate is distorted due to the photoisomerization of retinal. The hydrogen bond is weak in the unphotolyzed state and in the K intermediate, resulting in exchange of the hydrogen-bond acceptor to a water molecule in the K-to-L transition, relaxation of the polyene chain distortion, and generation of an alternative distortion near the Schiff base. The bound halide ion interacts with the protonated Schiff base through the water molecule bound to the protonated Schiff base. In the L-to-N transition, the hydrogen acceptor of the protonated Schiff base switches from the water molecule to another species, although the strong hydrogen bond of the protonated Schiff base remains. This paper reports the first observation of sequential changes in the RR spectra in the pHR photocycle, provides information on the structural evolution of the retinal chromophore, and proposes a model for chloride ion translocation in pHR.
我们通过在纳秒至毫秒时间尺度上使用时间分辨共振拉曼（RR）光谱探索视黄醛发色团在光循环过程中的连续结构变化，揭示了嗜盐菌视紫红质（pHR）中的氯离子泵浦机制。获得了未光解状态下视黄醛发色团以及pHR的三种中间体的一系列RR光谱。通过对时间分辨RR光谱中C═C和C-C伸缩带进行奇异值分解分析，我们确定了K、L和N中间体的光谱。我们专注于RR谱带的结构标记以探索视黄醛发色团的结构。在未光解状态下，视黄醛发色团处于平面全反式、15-反式几何构型。结合的离子影响多烯链，但不与质子化席夫碱相互作用。在观察到的中间体中，发色团处于13-顺式构型。K中间体中的发色团由于视黄醛的光异构化而发生扭曲。在未光解状态和K中间体中氢键较弱，导致在从K到L的转变中氢键受体与水分子交换，多烯链扭曲松弛，并在席夫碱附近产生另一种扭曲。结合的卤离子通过与质子化席夫碱结合的水分子与质子化席夫碱相互作用。在从L到N的转变中，质子化席夫碱的氢受体从水分子切换到另一种物质，尽管质子化席夫碱的强氢键仍然存在。本文首次报道了pHR光循环中RR光谱的连续变化，提供了视黄醛发色团结构演变的信息，并提出了pHR中氯离子转运的模型。
