A Protein Environment-Modulated Energy Dissipation Channel in LHCII Antenna Complex

The major light-harvesting complex of photosystem II (LHCII) is the main contributor to sunlight energy harvesting in plants. The flexible design of LHCII underlies a photoprotective mechanism whereby this complex switches to a dissipative state in response to high light stress, allowing the rapid dissipation of excess excitation energy (non-photochemical quenching, NPQ). In this work, we locked single LHCII trimers in a quenched conformation after immobilization of the complexes in polyacrylamide gels to impede protein interactions. A comparison of their pigment excited-state dynamics with quenched LHCII aggregates in buffer revealed the presence of a new spectral band at 515 nm arising after chlorophyll excitation. This is suggested to be the signature of a carotenoid excited state, linked to the quenching of chlorophyll singlet excited states. Our data highlight the marked sensitivity of pigment excited-state dynamics in LHCII to structural changes induced by the environment. [Display omitted] •Quenched and unquenched LHCII were studied in gel under aggregation-free conditions•Ultrafast spectroscopy revealed a new spectral band at 515 nm•The amplitude of the band correlates with quenching in LHCII trimers•The new band is due to carotenoid-Chl interaction modulated by LHCII conformation Physical Optics; Molecular Structure; Optical Property