The Structure and Mechanism of Energy Transfer in Phycobilisomes

Phycobilisomes (PBSs) are the major light-harvesting antenna of photosynthesis in cyanobacteria and red algae. Different types of PBSs exhibit a basic structure: a central core that interacts with photosystem II (PSII) and peripheral rods that are attached to the core and that expand the light-absorption cross-section area. This review summarizes recent progress in the study of PBS structures, with an emphasis on protein–bilin chromophore interactions. We describe the mechanisms of excitation energy transfer (EET) in PBSs with near-unity efficiency, as recent studies using two-dimensional electron spectroscopy showed that both Förster EET and coherent EET are involved in this process. Recent studies that provided insights into the mechanism of the PBS–thylakoid membrane association, particularly of PBS-PSII interactions, are also described. In addition, we discuss progress and some unsettled issues from studies on state transitions, which regulate energy distribution between PSII and PSI, in PBS-containing organisms.