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Protection from too much light.

​Photosynthetic organisms protect themselves from too much light using pigment photoswitches that absorb excess energy. American scientists (Berkeley, Michigan State University) and French researchers (SB2SM team) analyzed the structure of an active, energy-dissipating form of the orange carotenoid protein (OCP) from a cyanobacterium.

Published on 26 June 2015

​Pigment-protein and pigment-pigment interactions are of fundamental importance to the light-harvesting and photoprotective functions essential to oxygenic photosynthesis. The orange carotenoid protein (OCP) functions as both a sensor of light and effector of photoprotective energy dissipation in cyanobacteria. We report the atomic-resolution structure of an active form of the OCP consisting of the N-terminal domain and a single noncovalently bound carotenoid pigment. The crystal structure, combined with additional solution-state structural data, reveals that OCP photoactivation is accompanied by a 12 angstrom translocation of the pigment within the protein and a reconfiguration of carotenoid-protein interactions. Our results identify the origin of the photochromic changes in the OCP triggered by light and reveal the structural determinants required for interaction with the light-harvesting antenna during photoprotection.



Figure: Structures of the OCP and the RCP (Red Carotenoid Protein) superposed and position change of the carotenoid.

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