title: Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids.
abstract: Photosystem I (PSI) is the dominant photosystem in cyanobacteria and it plays a pivotal role in cyanobacterial metabolism. Despite its biological importance, the native organization of PSI in cyanobacterial thylakoid membranes is poorly understood. Here, we use atomic force microscopy (AFM) to show that ordered, extensive macromolecular arrays of PSI complexes are present in thylakoids fromThermosynechococcus elongatus,Synechococcussp PCC 7002, andSynechocystissp PCC 6803. Hyperspectral confocal fluorescence microscopy and three-dimensional structured illumination microscopy ofSynechocystissp PCC 6803 cells visualize PSI domains within the context of the complete thylakoid system. Crystallographic and AFM data were used to build a structural model of a membrane landscape comprising 96 PSI trimers and 27,648 chlorophyllamolecules. Rather than facilitating intertrimer energy transfer, the close associations between PSI primarily maximize packing efficiency; short-range interactions with Complex I and cytochromeb6fare excluded from these regions of the membrane, so PSI turnover is sustained by long-distance diffusion of the electron donors at the membrane surface. Elsewhere, PSI-photosystem II contact zones provide sites for docking phycobilisomes and the formation of megacomplexes. PSI-enriched domains in cyanobacteria might foreshadow the partitioning of PSI into stromal lamellae in plants, similarly sustained by long-distance diffusion of electron carriers.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Craig
authors.initials: C
authors.lastname: MacGregor-Chatwin
authors.affiliation: Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.|Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.
authors.forename: Melih
authors.initials: M
authors.lastname: Sener
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Samuel F H
authors.identifier: 0000-0002-3696-3509
authors.initials: SFH
authors.lastname: Barnett
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Andrew
authors.initials: A
authors.lastname: Hitchcock
authors.affiliation: Bioenergy and Defense Technologies Department, Sandia National Laboratories, Albuquerque, New Mexico 87185.
authors.forename: Meghan C
authors.initials: MC
authors.lastname: Barnhart-Dailey
authors.affiliation: Division of Molecular Biosciences, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: Karim
authors.identifier: 0000-0002-3854-9520
authors.initials: K
authors.lastname: Maghlaoui
authors.affiliation: Division of Molecular Biosciences, Faculty of Natural Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: James
authors.initials: J
authors.lastname: Barber
authors.affiliation: Bioenergy and Defense Technologies Department, Sandia National Laboratories, Albuquerque, New Mexico 87185.
authors.forename: Jerilyn A
authors.identifier: 0000-0003-2953-1721
authors.initials: JA
authors.lastname: Timlin
authors.affiliation: Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.|Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.|Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom c.n.hunter@sheffield.ac.uk.
authors.forename: C Neil
authors.identifier: 0000-0003-2533-9783
authors.initials: CN
authors.lastname: Hunter
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D046940:Synechococcus / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex