title: Very rapid phosphorylation kinetics suggest a unique role for Lhcb2 during state transitions in Arabidopsis.
abstract: Light-harvesting complex II (LHCII) contains three highly homologous chlorophyll-a/b-binding proteins (Lhcb1, Lhcb2 and Lhcb3), which can be assembled into both homo- and heterotrimers. Lhcb1 and Lhcb2 are reversibly phosphorylated by the action of STN7 kinase and PPH1/TAP38 phosphatase in the so-called state-transition process. We have developed antibodies that are specific for the phosphorylated forms of Lhcb1 and Lhcb2. We found that Lhcb2 is more rapidly phosphorylated than Lhcb1: 10 sec of 'state 2 light' results in Lhcb2 phosphorylation to 30% of the maximum level. Phosphorylated and non-phosphorylated forms of the proteins showed no difference in electrophoretic mobility and dephosphorylation kinetics did not differ between the two proteins. In state 2, most of the phosphorylated forms of Lhcb1 and Lhcb2 were present in super- and mega-complexes that comprised both photosystem (PS)I and PSII, and the state 2-specific PSI-LHCII complex was highly enriched in the phosphorylated forms of Lhcb2. Our results imply distinct and specific roles for Lhcb1 and Lhcb2 in the regulation of photosynthetic light harvesting.
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, 901 87, Umeå, Sweden; Department of Biosciences Biotechnologies and Pharmacology Sciences, Bari University, Via Amendola 165/A, 70126, Bari, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Leoni
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Pietrzykowska
authors.forename: Anett Z
authors.initials: AZ
authors.lastname: Kiss
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.forename: Luigi R
authors.initials: LR
authors.lastname: Ceci
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.forename: Stefan
authors.initials: S
authors.lastname: Jansson
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry*; D029681:Arabidopsis Proteins / Q000737:chemistry*; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D010766:Phosphorylation; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000737:chemistry; D020033:Protein Isoforms / Q000737:chemistry
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D020033:Protein Isoforms
keywords: Arabidopsis; LHCII; Lhcb2; phosphorylation; state transitions