In order to maximize their use of light energy in photosynthesis, plants have molecules that act as light-harvesting antennae, which collect light quanta and deliver them to the reaction centres, where energy conversion into a chemical form takes place. The functioning of the antenna responds to the extreme changes in the intensity of sunlight encountered in nature1,2,3. In shade, light is efficiently harvested in photosynthesis. However, in full sunlight, much of the energy absorbed is not needed and there are vitally important switches to specific antenna states, which safely dissipate the excess energy as heat2,3. This is essential for plant survival4, because it provides protection against the potential photo-damage of the photosynthetic membrane5. But whereas the features that establish high photosynthetic efficiency have been highlighted6, almost nothing is known about the molecular nature of the dissipative states. Recently, the atomic structure of the major plant light-harvesting antenna protein, LHCII, has been determined by X-ray crystallography7. Here we demonstrate that this is the structure of a dissipative state of LHCII. We present a spectroscopic analysis of this crystal form, and identify the specific changes in configuration of its pigment population that give LHCII the intrinsic capability to regulate energy flow. This provides a molecular basis for understanding the control of photosynthetic light-harvesting.
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This work was supported by UK Biotechnology and Biological Sciences Research Council, the INTRO2 European Union FP6 Marie Curie Research Training Network, The Royal Society, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) through the research programme of the Stichting voor Fundamenteel Onderzoek der Materie (FOM), President Foundation of CAS, the Knowledge Innovation Project of CAS, and the National Natural Sciences Foundation of China. The authors thank J. W. Borst of the MicroSpectroscopy Centre at Wageningen University for help in enabling and performing the FLIM measurements and for discussions.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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Pascal, A., Liu, Z., Broess, K. et al. Molecular basis of photoprotection and control of photosynthetic light-harvesting. Nature 436, 134–137 (2005) doi:10.1038/nature03795
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