Observation of dissipative chlorophyll-to-carotenoid energy transfer in light-harvesting complex II in membrane nanodiscs

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, because of the ultrafast timescales and large energy gaps involved, measurements lacked the temporal or spectral requirements. Second, 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. 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 membrane enhances two dissipative pathways, one of which was previously uncharacterized chlorophyll-to-carotenoid energy transfer. Our results highlight the sensitivity of the photophysics to the local environment, which may be used to control the balance between light harvesting and dissipation in vivo.