Tahara Shinya, Kuramochi Hikaru, Takeuchi Satoshi, Tahara Tahei
Molecular Spectroscopy Laboratory , RIKEN , 2-1 Hirosawa , Wako 351-0198 , Japan.
Ultrafast Spectroscopy Research Team , RIKEN Center for Advanced Photonics (RAP) , 2-1 Hirosawa , Wako 351-0198 , Japan.
J Phys Chem Lett. 2019 Sep 19;10(18):5422-5427. doi: 10.1021/acs.jpclett.9b02283. Epub 2019 Aug 30.
Bacteriorhodopsin is a prototypical photoreceptor protein that functions as a light-driven proton pump. The retinal chromophore of bacteriorhodopsin undergoes C═C trans-to-cis isomerization upon photoexcitation, and it has been believed to be the first event that triggers the cascaded structural changes in bacteriorhodopsin. We investigated the protein dynamics of bacteriorhodopsin using deep-ultraviolet resonance femtosecond stimulated Raman spectroscopy. It was found that the stimulated Raman signals of tryptophan and tyrosine residues exhibit significant changes within 0.2 ps after photoexcitation while they do not noticeably change during the isomerization process. This result implies that the protein environment changes first, and its change is small during isomerization. The obtained femtosecond stimulated Raman data indicate that ultrafast change is induced in the protein part by the sudden creation of the large dipole of the excited-state chromophore, providing an environment that realizes efficient and selective isomerization.
细菌视紫红质是一种典型的光感受器蛋白，其功能是作为光驱动质子泵。细菌视紫红质的视黄醛发色团在光激发时会发生C═C反式到顺式的异构化，并且一直被认为是触发细菌视紫红质级联结构变化的首个事件。我们使用深紫外共振飞秒受激拉曼光谱研究了细菌视紫红质的蛋白质动力学。结果发现，色氨酸和酪氨酸残基的受激拉曼信号在光激发后0.2皮秒内呈现出显著变化，而在异构化过程中它们没有明显变化。这一结果表明蛋白质环境首先发生变化，并且在异构化过程中其变化很小。所获得的飞秒受激拉曼数据表明，激发态发色团的大偶极子的突然产生在蛋白质部分诱导了超快变化，从而提供了一个实现高效且选择性异构化的环境。
