title: Dimerization of core complexes as an efficient strategy for energy trapping in Rhodobacter sphaeroides.
abstract: In the purple phototrophic bacterium Rhodobacter sphaeroides, light harvesting LH2 complexes transfer absorbed solar energy to RC-LH1-PufX core complexes, which are mainly found in the dimeric state. Many other purple phototrophs have monomeric core complexes and the basis for requiring dimeric cores is not fully established, so we analysed strains of Rba. sphaeroides that contain either native dimeric core complexes or altered monomeric cores harbouring a deletion of the first 12 residues from the N-terminus of PufX, which retains the PufX polypeptide but removes the major determinant of core complex dimerization. Membranes were purified from strains with dimeric or monomeric cores, and with either high or low levels of the LH2 complex. Samples were interrogated with absorption, steady-state fluorescence, and picosecond time-resolved fluorescence kinetic spectroscopies to reveal their light-harvesting and energy trapping properties. We find that under saturating excitation light intensity the photosynthetic membranes containing LH2 and monomeric core complexes have fluorescence lifetimes nearly twice that of membranes with LH2 plus dimeric core complexes. This trend of increased lifetime is maintained with RCs in the open state as well, and for two different levels of LH2 content. Thus, energy trapping is more efficient when photosynthetic membranes of Rba. sphaeroides consist of RC-LH1-PufX dimers and LH2 complexes.
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411, Estonia.
authors.forename: Manoop
authors.initials: M
authors.lastname: Chenchiliyan
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411, Estonia.
authors.forename: Kõu
authors.initials: K
authors.lastname: Timpmann
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411, Estonia.
authors.forename: Erko
authors.initials: E
authors.lastname: Jalviste
authors.affiliation: School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Adams
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: C Neil
authors.initials: CN
authors.lastname: Hunter
authors.affiliation: Institute of Physics, University of Tartu, W. Ostwald Str. 1, Tartu 50411, Estonia; Institute of Molecular and Cell Biology, University of Tartu, Riia 23, Tartu 51010, Estonia. Electronic address: arvi.freiberg@ut.ee.
authors.forename: Arvi
authors.initials: A
authors.lastname: Freiberg
mesh_terms: D000465:Algorithms; D020130:Bacterial Chromatophores / Q000378:metabolism* / Q000528:radiation effects; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004735:Energy Transfer / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D010788:Photosynthesis / Q000528:radiation effects; D055503:Protein Multimerization / Q000528:radiation effects; D012242:Rhodobacter sphaeroides / Q000378:metabolism* / Q000528:radiation effects; D013053:Spectrophotometry
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; C088749:PufX protein, Rhodobacter
keywords: LH1; LH2; Light harvesting; Photosynthesis; Photosynthetic excitons; RC