Conformational Changes in Light-Harvesting Complex II Trimer Depending on Its Binding Location

Abstract In green plants, the light-harvesting complex II (LHCII) trimer functions as a major antenna complex to the photosystem II (PSII) complex and a quencher to protect it from photooxidative damage. Theoretical studies on the structure of the LHCII trimer have demonstrated that excitation energy transfer between chlorophylls (Chls) can be modulated by its exquisite conformational fluctuation. However, the conformational changes in the LHCII trimer depending on its binding location have not yet been investigated, even though protein-protein interactions tend to lead conformational changes. In this study, we investigated the conformational changes in LHCII by analyzing an identical LHCII trimer comprising three different photosystem supercomplexes—PSII–LHCII supercomplexes (C2S2 type and C2S2M2L2 type) and PSI–LHCI–LHCII supercomplex—from the green alga Chlamydomonas reinhardtii. Consequently, the distinct differences in Chl configurations as well as polypeptide conformations of the LHCII trimers were detected based on where LHCII binds. Our analysis of the configurational factors between Chls suggests that these configurational changes lead to higher light-harvesting compatibilities in the PSII–LHCII supercomplex (C2S2M2L2 type) and PSI–LHCI–LHCII supercomplex. This study suggests a fine-tuned mechanism of energy transfer dynamics in LHCII trimers by regulation of protein-protein interactions.