Key Laboratory of Theoretical and Computational Photochemistry Ministry of Education, College of Chemistry, Beijing Normal University, Beijing, 100875, China.
College of Chemistry and Material Science, Sichuan Normal University, Chengdu, 610068, China.
Angew Chem Int Ed Engl. 2021 Aug 16;60(34):18688-18693. doi: 10.1002/anie.202104853. Epub 2021 Jul 16.
Phytochrome proteins are light receptors that play a pivotal role in regulating the life cycles of plants and microorganisms. Intriguingly, while cyanobacterial phytochrome Cph1 and cyanobacteriochrome AnPixJ use the same phycocyanobilin (PCB) chromophore to absorb light, their excited-state behavior is very different. We employ multiscale calculations to rationalize the different early photoisomerization mechanisms of PCB in Cph1 and AnPixJ. We found that their electronic S , T , and S potential minima exhibit distinct geometric and electronic structures due to different hydrogen bond networks with the protein environment. These specific interactions influence the S electronic structures along the photoisomerization paths, ultimately leading to internal conversion in Cph1 but intersystem crossing in AnPixJ. This explains why the excited-state relaxation in AnPixJ is much slower (ca. 100 ns) than in Cph1 (ca. 30 ps). Further, we predict that efficient internal conversion in AnPixJ can be achieved upon protonating the carboxylic group that interacts with PCB.
光敏色素蛋白是一类光受体，在调控植物和微生物的生命周期方面发挥着关键作用。有趣的是，虽然蓝藻光敏色素 Cph1 和蓝藻藻胆体 AnPixJ 使用相同的藻红胆素（PCB）发色团来吸收光，但它们的激发态行为却非常不同。我们采用多尺度计算方法来合理说明 Cph1 和 AnPixJ 中 PCB 不同的早期光异构化机制。我们发现，由于与蛋白质环境的氢键网络不同，它们的 S、T 和 S 势能极小值表现出明显不同的几何和电子结构。这些特定的相互作用影响着光异构化路径上的 S 电子结构，最终导致 Cph1 中的内转换和 AnPixJ 中的系间窜越。这解释了为什么 AnPixJ 中的激发态弛豫过程（约 100 ns）比 Cph1 中的（约 30 ps）慢得多。此外，我们预测，在与 PCB 相互作用的羧酸基团质子化后，AnPixJ 中的有效内转换可以实现。
