title: Energy-dissipative supercomplex of photosystem II associated with LHCSR3 in Chlamydomonas reinhardtii.
abstract: Plants and green algae have a low pH-inducible mechanism in photosystem II (PSII) that dissipates excess light energy, measured as the nonphotochemical quenching of chlorophyll fluorescence (qE). Recently, nonphotochemical quenching 4 (npq4), a mutant strain of the green alga Chlamydomonas reinhardtii that is qE-deficient and lacks the light-harvesting complex stress-related protein 3 (LHCSR3), was reported [Peers G, et al. (2009) Nature 462(7272):518-521]. Here, applying a newly established procedure, we isolated the PSII supercomplex and its associated light-harvesting proteins from both WT C. reinhardtii and the npq4 mutant grown in either low light (LL) or high light (HL). LHCSR3 was present in the PSII supercomplex from the HL-grown WT, but not in the supercomplex from the LL-grown WT or mutant. The purified PSII supercomplex containing LHCSR3 exhibited a normal fluorescence lifetime at a neutral pH (7.5) by single-photon counting analysis, but a significantly shorter lifetime at pH 5.5, which mimics the acidified lumen of the thylakoid membranes in HL-exposed chloroplasts. The switch from light-harvesting mode to energy-dissipating mode observed in the LHCSR3-containing PSII supercomplex was sensitive to dicyclohexylcarbodiimide, a protein-modifying agent specific to protonatable amino acid residues. We conclude that the PSII-LHCII-LHCSR3 supercomplex formed in the HL-grown C. reinhardtii cells is capable of energy dissipation on protonation of LHCSR3.
authors.affiliation: Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki 444-8585, Japan.
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Tokutsu
authors.forename: Jun
authors.initials: J
authors.lastname: Minagawa
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism*; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004735:Energy Transfer / Q000187:drug effects / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects / Q000528:radiation effects; D011522:Protons; D011994:Recombinant Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011522:Protons; D011994:Recombinant Proteins; D004024:Dicyclohexylcarbodiimide
keywords: high light stress; light acclimation; photosynthesis; time-resolved fluorescence