Microsecond and millisecond dynamics in the photosynthetic protein LHCSR1 observed by single-molecule correlation spectroscopy

Protein flexibility is essential for the robustness of biological systems, yet the dynamics underlying this flexibility are difficult to observe, because they are small, fast, and stochastic. Photoprotection in plants is critical for robust growth under highly variable sunlight, but the complexity of photosynthetic proteins means that identifying conformational states and dynamics responsible is challenging. Here, we develop a method using the correlation function of the fluorescence lifetime to characterize multiple dynamical processes in single proteins. By applying this method to the protein Light-Harvesting Complex Stress Related 1 (LHCSR1), we identify two local protein motions that control quenching of excess sunlight, which is a photoprotective effect. Our analytical approach enables a structure-based understanding of the photoprotective mechanisms in green plants.