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Title: Integration of energy and electron transfer processes in the photosynthetic membrane of Rhodobacter sphaeroides

Photosynthesis converts absorbed solar energy to a protonmotive force, which drives ATP synthesis. The membrane network of chlorophyll–protein complexes responsible for light absorption, photochemistry and quinol (QH 2) production has been mapped in the purple phototrophic bacterium Rhodobacter (Rba.) sphaeroides using atomic force microscopy (AFM), but the membrane location of the cytochrome bc 1 (cytbc 1) complexes that oxidise QH 2 to quinone (Q) to generate a protonmotive force is unknown. We labelled cytbc 1 complexes with gold nanobeads, each attached by a Histidine 10 (His 10)-tag to the C-terminus of cytc1. Electron microscopy (EM) of negatively stained chromatophore vesicles showed that the majority of the cytbc 1 complexes occur as dimers in the membrane. The cytbc 1 complexes appeared to be adjacent to reaction centre light-harvesting 1-PufX (RC-LH1-PufX) complexes, consistent with AFM topographs of a gold-labelled membrane. His-tagged cytbc1 complexes were retrieved from chromatophores partially solubilised by detergent; RC-LH1-PufX complexes tended to co-purify with cytbc 1, whereas LH2 complexes became detached, consistent with clusters of cytbc1 complexes close to RC-LH1-PufX arrays, but not with a fixed, stoichiometric cytbc 1-RC-LH1- PufX supercomplex. This information was combined with a quantitative mass spectrometry (MS) analysis of the RC, cytbc 1, ATP synthase,more » cytaa 3 and cytcbb 3 membrane protein complexes, to construct an atomic-level model of a chromatophore vesicle comprising 67 LH2 complexes, 11 LH1-RC-PufX dimers & 2 RC-LH1-PufX monomers, 4 cytbc 1 dimers and 2 ATP synthases. In conclusion, simulation of the interconnected energy, electron and proton transfer processes showed a halfmaximal ATP turnover rate for a light intensity equivalent to only 1% of bright sunlight. Thus, the photosystem architecture of the chromatophore is optimised for growth at low light intensities.« less
 [1] ;  [1] ;  [2] ;  [3] ;  [1] ;  [1] ;  [4] ;  [5] ;  [2] ;  [1]
  1. Univ. of Sheffield (United Kingdom). Dept. of Molecular Biology and Biotechnology
  2. Univ. of Illinois, Urbana-Champaign, IL (United States). Beckman Inst. for Advanced Science and Technology; Univ. of Illinois, Urbana-Champaign, IL (United States). Dept. of Physics
  3. Univ. of Sheffield (United Kingdom). Dept. of Molecular Biology and Biotechnology; Univ. of Sheffield (United Kingdom). ChELSI Inst, Dept. of Chemical and Biological Engineering
  4. Univ. of Sheffield (United Kingdom). ChELSI Inst, Dept. of Chemical and Biological Engineering
  5. Univ. of Sheffield (United Kingdom). Dept. of Chemistry
Publication Date:
OSTI Identifier:
Grant/Contract Number:
SC0001035; EP/I012060/1; 9P41GM104601; MCB-1157615
Published Article
Journal Name:
Biochimica et Biophysica Acta - Bioenergetics
Additional Journal Information:
Journal Volume: 1837; Journal Issue: 10; Journal ID: ISSN 0005-2728
Research Org:
Energy Frontier Research Centers (EFRC); Photosynthetic Antenna Research Center (PARC)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Engineering and Physical Sciences Research Council (United Kingdom); Biotechnology and Biological Sciences Research Council (United Kingdom); National Science Foundation (NSF); National Institutes of Health (NIH)
Contributing Orgs:
PARC partners with Washington University in St. Louis (lead); University of California, Riverside; University of Glasgow, UK; Los Alamos National Laboratory; University of New Mexico; New Mexico Corsortium; North Carolina State University; Northwestern University; Oak Ridge National Laboratory; University of Pennsylvania; Sandia National Laboratories; University of Sheffield, UK
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; solar (fuels); photosynthesis (natural and artificial); biofuels (including algae and biomass); bio-inspired; charge transport; membrane; synthesis (novel materials); synthesis (self-assembly); bacterial photosynthesis; cytochrome bc1; atomic force microscopy; electron microscopy; quinone; membrane modeling