Department of Physics, Freie Universität Berlin, Berlin, Germany.
Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Group Protein X-ray Crystallography and Signal Transduction, Berlin, Germany.
Nat Chem. 2022 Jul;14(7):823-830. doi: 10.1038/s41557-022-00944-x. Epub 2022 May 16.
The biological function of phytochromes is triggered by an ultrafast photoisomerization of the tetrapyrrole chromophore biliverdin between two rings denoted C and D. The mechanism by which this process induces extended structural changes of the protein is unclear. Here we report ultrafast proton-coupled photoisomerization upon excitation of the parent state (Pfr) of bacteriophytochrome Agp2. Transient deprotonation of the chromophore's pyrrole ring D or ring C into a hydrogen-bonded water cluster, revealed by a broad continuum infrared band, is triggered by electronic excitation, coherent oscillations and the sudden electric-field change in the excited state. Subsequently, a dominant fraction of the excited population relaxes back to the Pfr state, while ~35% follows the forward reaction to the photoproduct. A combination of quantum mechanics/molecular mechanics calculations and ultrafast visible and infrared spectroscopies demonstrates how proton-coupled dynamics in the excited state of Pfr leads to a restructured hydrogen-bond environment of early Lumi-F, which is interpreted as a trigger for downstream protein structural changes.
植物色素的生物功能是由四吡咯生色团胆绿素在 C 和 D 两个环之间的超快光异构化触发的。目前尚不清楚这一过程如何诱导蛋白质的扩展结构变化。本文报道了细菌叶绿素 Agp2 的 Pfr 态激发时超快质子耦合光异构化。瞬态去质子化的生色团吡咯环 D 或环 C 进入氢键结合的水簇，通过宽连续红外带揭示，由电子激发、相干振荡和激发态中的突然电场变化引发。随后，大部分激发态的激发态回到 Pfr 态，而~35%的激发态遵循向前反应到光产物。量子力学/分子力学计算和超快可见和红外光谱的组合表明，Pfr 态的激发态中的质子耦合动力学如何导致早期 Lumi-F 的氢键环境重构，这被解释为下游蛋白质结构变化的触发因素。
