Evidence for Protein Dynamics-Induced Energy Transfer Pathway Changes in Photosynthetic Complexes.

Photosystem I (PSI) is a chlorophyll-binding protein complex that plays a central role in photosynthesis. PSI isolated from cyanobacteria, Thermosynechococcus vestitus, contains a light-harvesting system that consists of approximately 100 chlorophyll a molecules. The effect of the protein fluctuation dynamics on the excitation energy migration within the pigment array is fundamentally important. In 2009, Brecht and co-workers proposed that protein dynamics can induce variations in the excitation energy transfer (EET) pathways within PSI ( Brecht et al. Proc. Natl. Acad. Sci. U. S. A.2009, 106, 11857-11861.). However, direct evidence for the tuning of EET pathways by protein dynamics is still lacking. Recently, we used a cryogenic single-molecule excitation-emission spectroscopy (SMEES) technique to determine the spatio-energetic relationship between antenna molecules and terminal emitters within PSI ( Zhang et al. J. Phys. Chem. B2026, 130, 104-118.). Here, we further implement time-resolved SMEES measurements on PSIs at 80 K. Our results not only provide evidence for protein dynamics-induced modification of EET pathways but also validate the molecular mechanisms of PSI fluorescence blinking.