title: Crystal structure of plant light-harvesting complex shows the active, energy-transmitting state.
abstract: Plants dissipate excess excitation energy as heat by non-photochemical quenching (NPQ). NPQ has been thought to resemble in vitro aggregation quenching of the major antenna complex, light harvesting complex of photosystem II (LHC-II). Both processes are widely believed to involve a conformational change that creates a quenching centre of two neighbouring pigments within the complex. Using recombinant LHC-II lacking the pigments implicated in quenching, we show that they have no particular role. Single crystals of LHC-II emit strong, orientation-dependent fluorescence with an emission maximum at 680 nm. The average lifetime of the main 680 nm crystal emission at 100 K is 1.31 ns, but only 0.39 ns for LHC-II aggregates under identical conditions. The strong emission and comparatively long fluorescence lifetimes of single LHC-II crystals indicate that the complex is unquenched, and that therefore the crystal structure shows the active, energy-transmitting state of LHC-II. We conclude that quenching of excitation energy in the light-harvesting antenna is due to the molecular interaction with external pigments in vitro or other pigment-protein complexes such as PsbS in vivo, and does not require a conformational change within the complex.
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
authors.forename: Tiago
authors.initials: T
authors.lastname: Barros
authors.forename: Antoine
authors.initials: A
authors.lastname: Royant
authors.forename: Jörg
authors.initials: J
authors.lastname: Standfuss
authors.forename: Andreas
authors.initials: A
authors.lastname: Dreuw
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
mesh_terms: D001665:Binding Sites; D002734:Chlorophyll / Q000378:metabolism; D018360:Crystallography, X-Ray; D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry; D018532:Pisum sativum / Q000737:chemistry*; D017785:Photons; D010860:Pigments, Biological / Q000737:chemistry; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D013050:Spectrometry, Fluorescence; D018724:Spinacia oleracea / Q000737:chemistry; D013696:Temperature; D013997:Time Factors
chemical_list: D045342:Light-Harvesting Protein Complexes; D050505:Mutant Proteins; D010860:Pigments, Biological; D002734:Chlorophyll