Dissipative Pathways in Light-Harvesting Complex II Are Controlled by the Plant Membrane

Green plants prevent photodamage under high light conditions by dissipating excess energy as heat. Conformational changes of the photosynthetic antenna complexes activate dissipation by leveraging the sensitivity of the photophysics of the chlorophyll and carotenoids to their surrounding protein. However, the mechanisms and site of dissipation are still debated, largely due to two challenges. First, experiments have been performed in detergent, which can induce non-native conformations, or in vivo, where contributions from the multiple complexes cannot be disentangled and are further obfuscated by laser-induced artifacts. Second, because of the ultrafast timescales and large energy gaps involved, measurements lacked the temporal or spectral requirements. Here, we overcome both challenges by applying ultrabroadband two-dimensional electronic spectroscopy to the principal antenna complex, light-harvesting complex II, in a near-native membrane. The spectra show that the membrane enhances two dissipative pathways, one of which was hypothesized yet previously uncharacterized. Our results suggest a resting level of dissipation that may protect against sudden solar fluctuations, and highlight that this level can even be fine-tuned by the membrane environment.