Light affects the accessibility of the thylakoid light harvesting complex II (LHCII) phosphorylation site to the membrane protein kinase(s)

Biochemistry. 2003 Jan 28;42(3):728-38. doi: 10.1021/bi020451r.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Hydrolysis
  • Light*
  • Light-Harvesting Protein Complexes
  • Membrane Proteins / chemistry
  • Membrane Proteins / metabolism*
  • Models, Chemical
  • Peas / enzymology
  • Peas / metabolism
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Phosphorylation
  • Phosphothreonine / metabolism
  • Photons
  • Photosynthetic Reaction Center Complex Proteins / chemistry
  • Photosynthetic Reaction Center Complex Proteins / metabolism*
  • Plant Leaves / enzymology
  • Plant Leaves / metabolism
  • Protein Binding
  • Protein Conformation
  • Protein Kinases / chemistry
  • Protein Kinases / metabolism*
  • Temperature
  • Thylakoids / chemistry
  • Thylakoids / enzymology*
  • Thylakoids / metabolism
  • Trypsin / metabolism

Substances

  • Light-Harvesting Protein Complexes
  • Membrane Proteins
  • Peptide Fragments
  • Photosynthetic Reaction Center Complex Proteins
  • Phosphothreonine
  • Protein Kinases
  • light-harvesting complex II kinase
  • Trypsin