Abstract
Under changing light environment, light-harvesting complex II (LHCII) is redistributed between photosystem I (PSI) and photosystem II (PSII) to balance excited levels of each photosystem (state transitions). Recently, a protein complex composed of PSI, LHCIs and LHCIIs has been isolated, which supports the model for attachment of LHCIIs to PSI. However, the mechanism for detachment of LHCIIs from PSII, which should occur simultaneously during state transitions, still remains unclear. Here, we isolated a protein complex composed of PSII and LHCIIs, a so-called PSII-LHCII supercomplex, by using a Chlamydomonas reinhardtii mutant carrying histidine-tagged CP47 through nickel affinity chromatography and determined the structural changes during state transitions. Gel filtration chromatography showed that three different sizes of isolated PSII-LHCII supercomplexes existed. The proportion of each protein complex was changed during the course of state transition. We propose a molecular mechanism for the detachment of LHCIIs in state transitions.
