Department of Chemistry , Yale University , 225 Prospect Street , New Haven , Connecticut 06520 , United States.
J Phys Chem B. 2019 Jan 17;123(2):439-447. doi: 10.1021/acs.jpcb.8b10973. Epub 2019 Jan 3.
Photoreceptor proteins control vital cellular responses to light. The photocycle of the Slr1694 blue light using flavin photoreceptor is initiated by photoexcitation to a locally excited state within the flavin, followed by electron transfer from Tyr8 to the flavin and a proton relay from Tyr8 to the flavin via an intervening glutamine. Herein, the two-dimensional excited state potential energy surfaces associated with this double proton-transfer reaction are computed using the complete active space self-consistent-field method and multiconfigurational perturbation theory, including the protein and solvent environment with electrostatic embedding. The double proton-transfer reaction was found to be energetically unfavorable in the ground state and locally excited state but energetically favorable in the charge-transfer state corresponding to electron transfer from Tyr8 to the flavin. These results indicate that the proton-coupled electron transfer process is sequential, with electron transfer preceding double proton transfer, and that the double proton-transfer reaction is also sequential, with proton transfer from Tyr8 to Gln50 followed by proton transfer from Gln50 to the flavin. The barrier is lower for the first proton-transfer reaction, and both barriers are significantly influenced by geometrical changes within the active site, particularly the proton donor-acceptor distance as well as the protein environment. These calculations provide insight into the impact of protein reorganization and electrostatics on the excited electronic states prior to and during the double proton-transfer reaction. This interplay between excited states and the environment has implications for other photoreceptor proteins.
感光蛋白控制着细胞对光的重要反应。Slr1694 蓝光利用黄素光受体的光循环是由黄素内的局部激发态引发的，随后是 Tyr8 向黄素的电子转移和 Tyr8 通过 intervening Gln 向黄素的质子传递。在此，使用完全活性空间自洽场方法和多组态微扰理论，包括静电嵌入的蛋白质和溶剂环境，计算了与该双质子转移反应相关的二维激发态势能面。发现双质子转移反应在基态和局部激发态下能量不利，但在 Tyr8 向黄素的电子转移对应的电荷转移态下能量有利。这些结果表明质子耦合电子转移过程是顺序的，电子转移先于双质子转移，双质子转移反应也是顺序的，质子从 Tyr8 转移到 Gln50 然后从 Gln50 转移到黄素。第一个质子转移反应的势垒较低，两个势垒都受到活性位点内的几何变化的显著影响，特别是质子供体-受体距离以及蛋白质环境。这些计算深入了解了在双质子转移反应之前和期间，蛋白质重组和静电对激发电子态的影响。这种激发态与环境之间的相互作用对其他感光蛋白有影响。
