In situstructural determination of cyanobacterial phycobilisome-PSII supercomplex by STAgSPA strategy

Abstract

SummaryPhotosynthesis converting solar energy to chemical energy is one of the most important chemical reactions on earth1. In cyanobacteria, light energy is captured by antenna system phycobilisomes (PBSs) and transferred to photosynthetic reaction centers of photosystem II (PSII) and photosystem I (PSI)2. While most of the protein complexes involved in photosynthesis have been characterized byin vitrostructural analyses, how these protein complexes function togetherin vivois not well understood. Here we developed anin situstructural analysis strategy “STAgSPA” to successfully solve thein situstructure of PBS-PSII supercomplex from the cyanobacteriaSpirulina platensisFACHB-439 at resolution of ∼3.5Å. The structure reveals the unprecedented coupling details among adjacent PBSs and PSII dimers, and the collaborative energy transfer mechanism mediated by multiple “super-PBS” in cyanobacteria. Our results not only provide the insights for understanding the diversity of photosynthesis-related systems between prokaryotic cyanobacteria and eukaryotic red algae, but also a valuable methodological demonstration forin situhigh-resolution structural analysis in cellular or tissue samples.