Light-harvesting antenna systems in photosynthetic organisms harvest solar energy and transfer it to the photosynthetic reaction centres to initiate charge-separation and electron-transfer reactions. Diatoms are one of the important groups of oxyphototrophs and possess fucoxanthin chlorophyll a/c-binding proteins (FCPs) as light harvesters. The organization and association pattern of FCP with the photosystem II (PSII) core are unknown. Here we solved the structure of PSII–FCPII supercomplexes isolated from a diatom, Chaetoceros gracilis, by single-particle cryoelectron microscopy. The PSII–FCPII forms a homodimer. In each monomer, two FCP homotetramers and three FCP monomers are associated with one PSII core. The structure reveals a highly complicated protein–pigment network that is different from the green-type light-harvesting apparatus. Comparing these two systems allows the identification of energy transfer and quenching pathways. These findings provide structural insights into not only excitation-energy transfer mechanisms in the diatom PSII–FCPII, but also changes of light harvesters between the red- and green-lineage oxyphototrophs during evolution.
ASJC Scopus subject areas
- Plant Science