title: Zeaxanthin radical cation formation in minor light-harvesting complexes of higher plant antenna.
abstract: Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light-harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5% of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N) <==> LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.
authors.affiliation: Department of Chemistry, Hildebrand B77, University of California, Berkeley, California 94720-1460; Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Avenson
authors.affiliation: Department of Chemistry, Hildebrand B77, University of California, Berkeley, California 94720-1460; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720.
authors.forename: Tae Kyu
authors.initials: TK
authors.lastname: Ahn
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720.
authors.forename: Donatas
authors.initials: D
authors.lastname: Zigmantas
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720.
authors.forename: Krishna K
authors.initials: KK
authors.lastname: Niyogi
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720.
authors.forename: Zhirong
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Science and Technology, University of Verona, Italy 37134.
authors.forename: Matteo
authors.initials: M
authors.lastname: Ballottari
authors.affiliation: Department of Science and Technology, University of Verona, Italy 37134.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.affiliation: Department of Chemistry, Hildebrand B77, University of California, Berkeley, California 94720-1460; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720. Electronic address: GRFleming@lbl.gov.
authors.forename: Graham R
authors.initials: GR
authors.lastname: Fleming
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D002412:Cations; D019281:Dimerization; D018506:Gene Expression Regulation, Plant; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D018521:Plant Physiological Phenomena; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry / Q000379:methods; D019265:Spectroscopy, Near-Infrared; D020524:Thylakoids / Q000378:metabolism; D024341:Xanthophylls / Q000737:chemistry*; D065146:Zeaxanthins
chemical_list: D002412:Cations; D045342:Light-Harvesting Protein Complexes; D024341:Xanthophylls; D065146:Zeaxanthins