Structure of Phycobilisomes

Phycobilisomes (PBSs) are extremely large chromophore–protein complexes on the stromal side of the thylakoid membrane in cyanobacteria and red algae. The main function of PBSs is light harvesting, and they serve as antennas and transfer the absorbed energy to the reaction centers of two photosynthetic systems (photosystems I and II). PBSs are composed of phycobiliproteins and linker proteins. How phycobiliproteins and linkers are organized in PBSs and how light energy is efficiently harvested and transferred in PBSs are the fundamental questions in the study of photosynthesis. In this review, the structures of the red algae Griffithsia pacifica and Porphyridium purpureum are discussed in detail, along with the functions of linker proteins in phycobiliprotein assembly and in fine-tuning the energy state of chromophores.