Zhang Teng-Shuo, Fang Ye-Guang, Song Xiu-Fang, Fang Wei-Hai, Cui Ganglong
Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, Chemistry College, Beijing Normal University, Beijing 100875, P.R. China.
J Phys Chem Lett. 2020 Apr 2;11(7):2470-2476. doi: 10.1021/acs.jpclett.0c00294. Epub 2020 Mar 13.
We have employed the QM(CASPT2//CASSCF)/MM method to explore the excited-state isomerization and decay mechanism of a single-bond-rotation locked photoactive yellow protein (PYP) chromophore in wild-type and mutant proteins. The S state is a spectroscopically bright state in the Franck-Condon region. In this state, there exist two excited-state isomerization pathways separately related to the clockwise and anticlockwise rotations of the C=C bond. The clockwise path is favorable because of a small barrier of 2 kcal/mol and uses a novel bicycle-pedal unidirectional photoisomerization mechanism in which the involved two dihedral angles rotate asynchronously because of the reinforced hydrogen-bonding interaction between the chromophore and Cys69. Near the twisted S minimum, the chromophore hops to the S state via the S/S conical intersection. Finally, the R52A mutation has small effects on the excited-state properties and photoisomerization of the locked PYP chromophore. The present work provides new insights for understanding the photochemistry of PYP chromophores in protein surroundings.
我们采用了QM(CASPT2//CASSCF)/MM方法来探究野生型和突变型蛋白质中，单键旋转锁定的光活性黄色蛋白（PYP）发色团的激发态异构化和衰变机制。S态是弗兰克-康登区域内光谱学上的明亮态。在该状态下，存在两条分别与C=C键顺时针和逆时针旋转相关的激发态异构化途径。顺时针路径较为有利，因为其势垒较小，仅为2千卡/摩尔，且采用了一种新颖的自行车踏板式单向光异构化机制，其中由于发色团与半胱氨酸69之间增强的氢键相互作用，所涉及的两个二面角异步旋转。在扭曲的S态最小值附近，发色团通过S/S锥形交叉点跃迁至S态。最后，R52A突变对锁定的PYP发色团的激发态性质和光异构化影响较小。本研究为理解蛋白质环境中PYP发色团的光化学提供了新的见解。
