Tuesday February 10 2009
CEA
Crystal structure of plant light-harvesting complex shows the active, energy-transmitting state
CEA
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.
Reference:
“Crystal structure of plant light-harvesting complex shows the active, energy-transmitting state” Tiago Barros, Antoine Royant, Jörg Standfuss, Andreas Dreuw & Werner Kühlbrandt The EMBO Journal (2009) 28, 298-306.
Contact:
Antoine Royant
Institut de Biologie Structurale Jean-Pierre Ebel – UMR5075 CNRS-CEA-UJF
41 rue Jules Horowitz
38027 Grenoble Cedex 1
Téléphone : 04-38-78-96-28
Email : antoine.royant@ibs.fr