Inter-subunit Energy Transfer Processes in a Minimal Plant Photosystem II Supercomplex

Photosystem II (PSII) is an integral part of the photosynthesis machinery, in which several light-harvesting complexes rely on inter-complex excitonic energy transfer (EET) processes to channel energy to the reaction center. In this paper, we report on the direct observation of the inter-complex EET in a small PSII supercomplex from plants, containing the trimeric light-harvesting complex II (LHCII), the monomeric light-harvesting complex CP26 and the monomeric PSII core complex. Using two-dimensional electronic spectroscopy, we measure an average inter-complex EET time scale of 60±5 ps for excitations from the LHCII-CP26 peripheral antenna to the PSII core. The 2D electronic spectra also reveal that the transfer time scale is nearly constant over the excitation spectrum of 600-700 nm. Structure-based calculations reveal the contribution of each antenna complex to the measured inter-complex EET time. These results provide a step in elucidating the full inter-complex energy transfer network, which allows us to understand the efficiency and robustness of the PSII machinery