title: Phycobilisomes supply excitations to both photosystems in a megacomplex in cyanobacteria.
abstract: In photosynthetic organisms, photons are captured by light-harvesting antenna complexes, and energy is transferred to reaction centers where photochemical reactions take place. We describe here the isolation and characterization of a fully functional megacomplex composed of a phycobilisome antenna complex and photosystems I and II from the cyanobacterium Synechocystis PCC 6803. A combination of in vivo protein cross-linking, mass spectrometry, and time-resolved spectroscopy indicates that the megacomplex is organized to facilitate energy transfer but not intercomplex electron transfer, which requires diffusible intermediates and the cytochrome b6f complex. The organization provides a basis for understanding how phycobilisomes transfer excitation energy to reaction centers and how the energy balance of two photosystems is achieved, allowing the organism to adapt to varying ecophysiological conditions.
authors.affiliation: Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA.
authors.forename: Haijun
authors.initials: H
authors.lastname: Liu
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Dariusz M
authors.initials: DM
authors.lastname: Niedzwiedzki
authors.forename: Mindy
authors.initials: M
authors.lastname: Prado
authors.forename: Guannan
authors.initials: G
authors.lastname: He
authors.forename: Michael L
authors.initials: ML
authors.lastname: Gross
authors.forename: Robert E
authors.initials: RE
authors.lastname: Blankenship
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry; D004735:Energy Transfer; D005453:Fluorescence; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D045524:Phycobilisomes / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D011487:Protein Conformation; D046939:Synechocystis / Q000201:enzymology*
chemical_list: D003432:Cross-Linking Reagents; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes