title: Optimization of light harvesting and photoprotection: molecular mechanisms and physiological consequences.
abstract: The distinctive lateral organization of the protein complexes in the thylakoid membrane investigated by Jan Anderson and co-workers is dependent on the balance of various attractive and repulsive forces. Modulation of these forces allows critical physiological regulation of photosynthesis that provides efficient light-harvesting in limiting light but dissipation of excess potentially damaging radiation in saturating light. The light-harvesting complexes (LHCII) are central to this regulation, which is achieved by phosphorylation of stromal residues, protonation on the lumen surface and de-epoxidation of bound violaxanthin. The functional flexibility of LHCII derives from a remarkable pigment composition and configuration that not only allow efficient absorption of light and efficient energy transfer either to photosystem II or photosystem I core complexes, but through subtle configurational changes can also exhibit highly efficient dissipative reactions involving chlorophyll-xanthophyll and/or chlorophyll-chlorophyll interactions. These changes in function are determined at a macroscopic level by alterations in protein-protein interactions in the thylakoid membrane. The capacity and dynamics of this regulation are tuned to different physiological scenarios by the exact protein and pigment content of the light-harvesting system. Here, the molecular mechanisms involved will be reviewed, and the optimization of the light-harvesting system in different environmental conditions described.
authors.affiliation: Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, UK. p.horton@sheffield.ac.uk
authors.forename: Peter
authors.initials: P
authors.lastname: Horton
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D003080:Cold Temperature; D004579:Electron Transport; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D055668:Photochemical Processes; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D025941:Protein Interaction Mapping; D013472:Sunlight; D020524:Thylakoids / Q000378:metabolism* / Q000502:physiology / Q000528:radiation effects; D024341:Xanthophylls / Q000235:genetics / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D024341:Xanthophylls; D002734:Chlorophyll; C005613:violaxanthin