Photoinduced isomerization of the Photoactive Yellow Protein chromophore: a detailed theoretical investigation

在这个项目中，理论-包括大规模的电子结构和动力学计算-将被应用于提供详细的洞察生物感光器-光敏黄蛋白（PYP）的初始光事件。我们专注于最早期的PYP光循环中的事件，有关的反式到顺式异构化的-C=C-双键的PYP辅因子，去质子化的对羟基肉桂酰基发色团。异构化过程的机制和动力学可以被表征为高度复杂的，由于涉及几个坐标（两个扭转和一个弯曲模式）和发色团的局部环境的强烈影响。我们的理论分析将依赖于生色团在天然（蛋白质）环境和特定（模型）环境中的量子化学、电子结构和（半经典和量子）动力学计算。对于蛋白质环境中的发色团，主要重点将放在（i）在PYP的黑暗状态下建立不均匀性和（ii）仔细检查发色团异构化的初始阶段。对于模型环境，主要的重点将放在阐明氢的平面外（HOOP）坐标在异构化过程中的作用。这些问题的具体化应阐明诸如PYP的光活性（可异构化）形式、异构化坐标的含义/相互作用、反应途径和过程机制等尚未明确的方面。控制发色团的异构化被认为是一个令人兴奋的前景。

In this project, theory - including large-scale electronic structure and dynamical calculations - will be applied to provide detailed insight into the initial photoevents in a biological photoreceptor - the Photoactive Yellow Protein (PYP). We focus on the very earliest events in the PYP photocycle, related to the trans-to-cis isomerization of the -C=C- double bond of the PYP co-factor, the deprotonated p-hydroxycinnamoyl chromophore. The mechanism and dynamics of the isomerization process can be characterized as highly complex due to the involvement of several coordinates (two torsions and one bending mode) and the strong impact of the chromophore’s local environment. Our theoretical analysis will rest on quantum chemistry electronic structure and (semi-classical and quantum) dynamical calculations for the chromophore in the native (protein) environment and in a specific (model) environment. For the chromophore in the protein environment, the main emphasis will be placed on (i) establishing inhomogeneities in the dark-state of PYP and (ii) scrutinizing the initial phase of the chromophore’s isomerization. For the model environment, the main focus will be put on elucidating the role of the hydrogen out-of-plane (HOOP) coordinate in the isomerization process. Rationalization of these issues should illuminate such yet obscure aspects as the photoactive (isomerizable) form of PYP, implication/interplay of the isomerization coordinates, the reaction pathway and mechanism of the process. Acquiring control over the chromophore’s isomerization is considered an exciting perspective.