title: Aberrant assembly complexes of the reaction center light-harvesting 1 PufX (RC-LH1-PufX) core complex of Rhodobacter sphaeroides imaged by atomic force microscopy.
abstract: In the purple phototrophic bacterium Rhodobacter sphaeroides, many protein complexes congregate within the membrane to form operational photosynthetic units consisting of arrays of light-harvesting LH2 complexes and monomeric and dimeric reaction center (RC)-light-harvesting 1 (LH1)-PufX "core" complexes. Each half of a dimer complex consists of a RC surrounded by 14 LH1 αβ subunits, with two bacteriochlorophylls (Bchls) sandwiched between each αβ pair of transmembrane helices. We used atomic force microscopy (AFM) to investigate the assembly of single molecules of the RC-LH1-PufX complex using membranes prepared from LH2-minus mutants. When the RC and PufX components were also absent, AFM revealed a series of LH1 variants where the repeating α(1)β(1)(Bchl)2 units had formed rings of variable size, ellipses, and spirals and also arcs that could be assembly products. The spiral complexes occur when the LH1 ring has failed to close, and short arcs are suggestive of prematurely terminated LH1 complex assembly. In the absence of RCs, we occasionally observed captive proteins enclosed by the LH1 ring. When production of LH1 units was restricted by lowering the relative levels of the cognate pufBA transcript, we imaged a mixture of complete RC-LH1 core complexes, empty LH1 rings, and isolated RCs, leading us to conclude that once a RC associates with the first α1β1(Bchl)2 subunit, cooperative associations between subsequent subunits and the RC tend to drive LH1 ring assembly to completion.
authors.affiliation: From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and.
authors.forename: John D
authors.initials: JD
authors.lastname: Olsen
authors.affiliation: From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Adams
authors.affiliation: From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and the Department of Chemical and Biological Engineering, ChELSI Institute, University of Sheffield, Sheffield, S1 3JD, United Kingdom.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Jackson
authors.affiliation: the Department of Chemical and Biological Engineering, ChELSI Institute, University of Sheffield, Sheffield, S1 3JD, United Kingdom.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Dickman
authors.affiliation: From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and.
authors.forename: Pu
authors.initials: P
authors.lastname: Qian
authors.affiliation: From the Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, United Kingdom and c.n.hunter@sheffield.ac.uk.
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D021621:Imaging, Three-Dimensional; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D018625:Microscopy, Atomic Force / Q000379:methods*; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000187:drug effects / Q000378:metabolism*; D014461:Ultracentrifugation
chemical_list: D001426:Bacterial Proteins; D003902:Detergents; D045342:Light-Harvesting Protein Complexes; D050505:Mutant Proteins; D021122:Protein Subunits; C088749:PufX protein, Rhodobacter
keywords: Atomic Force Microscopy (AFM); Bacteria; Light Harvesting; Membrane Biogenesis; Membrane Protein; Photosynthesis; Reaction Center