title: A mechanism of energy dissipation in cyanobacteria.
abstract: When grown under a variety of stress conditions, cyanobacteria express the isiA gene, which encodes the IsiA pigment-protein complex. Overexpression of the isiA gene under iron-depletion stress conditions leads to the formation of large IsiA aggregates, which display remarkably short fluorescence lifetimes and thus a strong capacity to dissipate energy. In this work we investigate the underlying molecular mechanism responsible for chlorophyll fluorescence quenching. Femtosecond transient absorption spectroscopy allowed us to follow the process of energy dissipation in real time. The light energy harvested by chlorophyll pigments migrated within the system and eventually reaches a quenching site where the energy is transferred to a carotenoid-excited state, which dissipates it by decaying to the ground state. We compare these findings with those obtained for the main light-harvesting complex in green plants (light-harvesting complex II) and artificial light-harvesting antennas, and conclude that all of these systems show the same mechanism of energy dissipation, i.e., one or more carotenoids act as energy dissipators by accepting energy via low-lying singlet-excited S(1) states and dissipating it as heat.
authors.affiliation: Department of Physics and Astronomy, Faculty of Sciences, VU University, Amsterdam, The Netherlands. rberera@few.vu.nl
authors.forename: Rudi
authors.initials: R
authors.lastname: Berera
authors.forename: Ivo H M
authors.initials: IH
authors.lastname: van Stokkum
authors.forename: Sandrine
authors.initials: S
authors.lastname: d'Haene
authors.forename: John T M
authors.initials: JT
authors.lastname: Kennis
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
authors.forename: Jan P
authors.initials: JP
authors.lastname: Dekker
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism*; D004734:Energy Metabolism; D005453:Fluorescence; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008954:Models, Biological; D013057:Spectrum Analysis; D024341:Xanthophylls / Q000378:metabolism; D065146:Zeaxanthins
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D024341:Xanthophylls; D065146:Zeaxanthins; D002734:Chlorophyll; C076726:chlorophyll A binding protein CP43, Cyanobacteria; D002338:Carotenoids