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| light-harvesting complex II | |
|---|---|
| Name | Light-harvesting complex II |
| Caption | Trimeric pigment–protein complex from a chloroplast thylakoid membrane |
| Organism | Plants, Spinacia oleracea, Arabidopsis thaliana, cyanobacteria-like organisms |
| Type | Antenna complex |
light-harvesting complex II Light-harvesting complex II is the major peripheral antenna pigment–protein complex of photosynthetic chloroplasts in plants and many eukaryote algae, and analogous antenna assemblies occur in some cyanobacteria and proteobacteria. It forms trimeric units that bind chlorophylls and carotenoids to capture solar photons and funnel excitation energy to reaction centers in photosystem II, thereby linking pigment biochemistry with membrane protein architecture in the thylakoid system. Research on this complex intersects with structural biology labs using methods developed at facilities such as the European Molecular Biology Laboratory, techniques refined at the Max Planck Institute, and computational approaches from groups at Massachusetts Institute of Technology.
The core LHCII trimer is composed of homologous polypeptides encoded in the nuclear genomes of higher plants and chloroplast genomes of some algae, with sequences studied in Arabidopsis thaliana, Spinacia oleracea, and Chlamydomonas reinhardtii. High-resolution structures solved by groups at the European Synchrotron Radiation Facility and the Swiss Light Source revealed transmembrane helices coordinating pigment ligands, with protein folds comparable to those characterized by investigators at the Johns Hopkins University and University of Cambridge. Bound pigments include macrocycle cofactors such as chlorophyll a and chlorophyll b and xanthophyll carotenoids like lutein and violaxanthin, as cataloged in literature from the Royal Society and biochemical surveys at the University of California, Berkeley. The trimeric assembly interacts with membrane scaffolds and larger supercomplexes studied by researchers at the Max Planck Institute for Biophysics and the University of Oxford, and interfaces are modulated by lipid species whose roles were elucidated in collaborations including teams at the Scripps Research Institute and the Weizmann Institute of Science.
LHCII funnels excitation energy toward the photosystem II reaction center by resonance energy transfer pathways that have been experimentally dissected by groups at the California Institute of Technology and the University of Chicago. It participates in state transitions first characterized in physiology work at the University of Cambridge and biochemical work at the University of Paris and contributes to non-photochemical quenching mechanisms investigated by researchers at the University of Illinois and the Max Planck Institute for Plant Breeding Research. Functional studies link LHCII behavior to thylakoid membrane organization observed in imaging campaigns at the National Institutes of Health, with implications for light acclimation documented in field studies from institutions such as the Woods Hole Oceanographic Institution and the Smithsonian Institution.
Spectroscopic characterization of LHCII employed techniques pioneered at the Oak Ridge National Laboratory and at the Lawrence Berkeley National Laboratory, including ultrafast pump–probe spectroscopy and two-dimensional electronic spectroscopy used by teams at the University of Toronto and the University of Copenhagen. These studies revealed excitonic coupling among chlorophylls and carotenoids, energy transfer timescales comparable to those measured by researchers at the University of California, Santa Barbara and the University of Geneva, and carotenoid-mediated quenching routes explored in work associated with the Max Planck Institute of Molecular Plant Physiology. Computational modeling of excitonic states has been advanced in collaborations involving the Princeton University and the University of Vienna.
Biogenesis and turnover of LHCII are coordinated between nuclear and chloroplast gene expression machineries, with regulatory factors studied at the Carnegie Institution for Science and the Rothamsted Research institute. Post-translational modifications such as phosphorylation by kinases and dephosphorylation by phosphatases modulate LHCII migration between photosynthetic complexes, a process illuminated by genetic and biochemical work at the Salk Institute and the Heinrich Heine University Düsseldorf. Thylakoid membrane remodeling that affects LHCII distribution has been visualized in cryo-electron tomography studies from groups at the Max Planck Institute for Biochemistry and the European Molecular Biology Laboratory.
Gene families encoding LHCII polypeptides show expansion and diversification across taxa, with comparative genomics analyses carried out at the Broad Institute and the Joint Genome Institute revealing lineage-specific variants in Arabidopsis thaliana, Oryza sativa, and marine algae such as species studied by the Monterey Bay Aquarium Research Institute. Evolutionary patterns were reconstructed using phylogenetic frameworks developed at the Smithsonian Institution and the Natural History Museum, London, linking LHCII sequence shifts to ecological adaptations documented in surveys by the Australian National University and the University of Tokyo.
Engineering of light-harvesting complexes for enhanced biomass and bioenergy production has been explored in synthetic biology programs at the Massachusetts Institute of Technology, University of California, Davis, and the Imperial College London. Reconstitution approaches and mutagenesis strategies employed by labs at the University of Wisconsin–Madison and the ETH Zurich enable altered pigment composition and altered photoprotective responses. Methodologies for LHCII study include X-ray crystallography at the Diamond Light Source, cryo-electron microscopy at the National Center for Electron Microscopy, ultrafast spectroscopy facilities at the Fritz Haber Institute, and computational pipelines developed at the European Bioinformatics Institute and the National Center for Biotechnology Information.
Category:Photosynthetic protein complexes