title: Light affects the accessibility of the thylakoid light harvesting complex II (LHCII) phosphorylation site to the membrane protein kinase(s).
abstract: Redox-controlled, reversible phosphorylation of the thylakoid light harvesting complex II (LHCII) regulates its association with photosystems (PS) I or II and thus, energy distribution between the two photosystems (state transition). Illumination of solubilized LHCII enhances exposure of the phosphorylation site at its N-terminal domain to protein kinase(s) and tryptic cleavage in vitro [Zer et al. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 8277-8282]. Here we report that short illumination (5-10 min, 15-30 micromol m(-2) s(-1)) enhances the accessibility of LHCII phosphorylation site to kinase(s) activity also in isolated thylakoids. However, prolonged illumination or higher light intensities (30 min, 80-800 micromol m(-2) s(-1)) prevent phosphorylation of LHCII in the isolated membranes as well as in vivo, although redox-dependent protein kinase activity persists in the illuminated thylakoids toward exogenous solubilized LHCII. This phenomenon, ascribed to light-induced inaccessibility of the phosphorylation site to the protein kinase(s), affects in a similar way the accessibility of thylakoid LHCII N-terminal domain to tryptic cleavage. The illumination effect is not redox related, decreases linearly with temperature from 25 to 5 degrees C and may be ascribed to light-induced conformational changes in the complex causing lateral aggregation of dephosphorylated LHCII bound to and/or dissociated from PSII. The later state occurs under conditions allowing turnover of the phospho-LHCII phosphate. The light-induced inaccessibility of LHCII to the membrane-bound protein kinase reverses readily in darkness only if induced under LHCII-phosphate turnover conditions. Thus, phosphorylation prevents irreversible light-induced conformational changes in LHCII allowing lateral migration of the complex and the related state transition process.
authors.affiliation: Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel.
authors.forename: Hagit
authors.initials: H
authors.lastname: Zer
authors.forename: Martin
authors.initials: M
authors.lastname: Vink
authors.forename: Susana
authors.initials: S
authors.lastname: Shochat
authors.forename: Reinhold G
authors.initials: RG
authors.lastname: Herrmann
authors.forename: Bertil
authors.initials: B
authors.lastname: Andersson
authors.forename: Itzhak
authors.initials: I
authors.lastname: Ohad
mesh_terms: D006868:Hydrolysis; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008956:Models, Chemical; D018532:Pisum sativum / Q000201:enzymology / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D017785:Photons; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature; D020524:Thylakoids / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D010446:Peptide Fragments; D045322:Photosynthetic Reaction Center Complex Proteins; D010769:Phosphothreonine; D011494:Protein Kinases; C120337:light-harvesting complex II kinase; D014357:Trypsin