Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.
Department of Life Science and Technology, Tokyo Institute of Technology, Tokyo, Japan.
Nat Chem. 2022 Feb;14(2):153-159. doi: 10.1038/s41557-021-00841-9. Epub 2022 Jan 6.
Photosynthetic organisms convert sunlight to electricity with near unity quantum efficiency. Absorbed photoenergy transfers through a network of chromophores positioned within protein scaffolds, which fluctuate due to thermal motion. The resultant variation in the individual energy transfer steps has not yet been measured, and so how the efficiency is robust to this variation has not been determined. Here, we describe single-molecule pump-probe spectroscopy with facile spectral tuning and its application to the ultrafast dynamics of single allophycocyanin, a light-harvesting protein from cyanobacteria. We disentangled the energy transfer and energetic relaxation from nuclear motion using the spectral dependence of the dynamics. We observed an asymmetric distribution of timescales for energy transfer and a slower and more heterogeneous distribution of timescales for energetic relaxation, which was due to the impact of the protein environment. Collectively, these results suggest that energy transfer is robust to protein fluctuations, a prerequisite for efficient light harvesting.
光合生物以近乎统一的量子效率将阳光转化为电能。吸收的光能通过位于蛋白质支架内的发色团网络传递，由于热运动，这些发色团会发生波动。由于尚未测量单个能量转移步骤的这种变化，因此也无法确定效率对这种变化的稳健性。在这里，我们描述了具有简便光谱调谐功能的单分子泵浦探针光谱法及其在蓝藻捕光蛋白藻蓝蛋白的超快动力学中的应用。我们使用动力学的光谱依赖性将能量转移和核运动的能量弛豫解耦。我们观察到能量转移的时间尺度呈不对称分布，而能量弛豫的时间尺度分布较慢且更不均匀，这是由于蛋白质环境的影响。总的来说，这些结果表明，能量转移对蛋白质波动具有鲁棒性，这是高效捕光的前提。
