title: Structural organization of an intact phycobilisome and its association with photosystem II.
abstract: Phycobilisomes (PBSs) are light-harvesting antennae that transfer energy to photosynthetic reaction centers in cyanobacteria and red algae. PBSs are supermolecular complexes composed of phycobiliproteins (PBPs) that bear chromophores for energy absorption and linker proteins. Although the structures of some individual components have been determined using crystallography, the three-dimensional structure of an entire PBS complex, which is critical for understanding the energy transfer mechanism, remains unknown. Here, we report the structures of an intact PBS and a PBS in complex with photosystem II (PSII) from Anabaena sp. strain PCC 7120 using single-particle electron microscopy in combination with biochemical and molecular analyses. In the PBS structure, all PBP trimers and the conserved linker protein domains were unambiguously located, and the global distribution of all chromophores was determined. We provide evidence that ApcE and ApcF are critical for the formation of a protrusion at the bottom of PBS, which plays an important role in mediating PBS interaction with PSII. Our results provide insights into the molecular architecture of an intact PBS at different assembly levels and provide the basis for understanding how the light energy absorbed by PBS is transferred to PSII.
authors.affiliation: 1] State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China [2] Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China [3] Current address: MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK.
authors.forename: Leifu
authors.initials: L
authors.lastname: Chang
authors.affiliation: State Key Laboratory of Protein and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing 100871, China.
authors.forename: Xianwei
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Protein and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing 100871, China.
authors.forename: Yanbing
authors.initials: Y
authors.lastname: Li
authors.affiliation: 1] State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China [2] Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Cui-Cui
authors.initials: CC
authors.lastname: Liu
authors.affiliation: 1] State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China [2] Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.affiliation: 1] State Key Laboratory of Protein and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing 100871, China [2] Key Laboratory of Phycology of CAS, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei 430072, China.
authors.forename: Jindong
authors.initials: J
authors.lastname: Zhao
authors.affiliation: 1] State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China [2] Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Sen-Fang
authors.initials: SF
authors.lastname: Sui
mesh_terms: D017033:Anabaena / Q000737:chemistry* / Q000378:metabolism; D008854:Microscopy, Electron; D008958:Models, Molecular; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D045524:Phycobilisomes / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation
chemical_list: D045332:Photosystem II Protein Complex; D045524:Phycobilisomes