title: Dramatic Domain Rearrangements of the Cyanobacterial Orange Carotenoid Protein upon Photoactivation.
abstract: Photosynthetic cyanobacteria make important contributions to global carbon and nitrogen budgets. A protein known as the orange carotenoid protein (OCP) protects the photosynthetic apparatus from damage by dissipating excess energy absorbed by the phycobilisome, the major light-harvesting complex in many cyanobacteria. OCP binds one carotenoid pigment, but the color of this pigment depends on conditions. It is orange in the dark and red when exposed to light. We modified the orange and red forms of OCP by using isotopically coded cross-linking agents and then analyzed the structural features by using liquid chromatography and tandem mass spectrometry. Unequivocal cross-linking pairs uniquely detected in red OCP indicate that, upon photoactivation, the OCP N-terminal domain (NTD) and C-terminal domain (CTD) reorient relative to each other. Our data also indicate that the intrinsically unstructured loop connecting the NTD and CTD not only is involved in the interaction between the two domains in orange OCP but also, together with the N-terminal extension, provides a structural buffer system facilitating an intramolecular breathing motion of the OCP, thus helping conversion back and forth from the orange to red form during the OCP photocycle. These results have important implications for understanding the molecular mechanism of action of cyanobacterial photoprotection.
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Haijun
authors: H
authors: Liu
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Hao
authors: H
authors: Zhang
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Gregory S
authors: GS
authors: Orf
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Yue
authors: Y
authors: Lu
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Jing
authors: J
authors: Jiang
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Jeremy D
authors: JD
authors: King
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Nathan R
authors: NR
authors: Wolf
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Michael L
authors: ML
authors: Gross
authors: Department of Biology, ‡Photosynthetic Antenna Research Center (PARC), and §Department of Chemistry, Washington University in St. Louis , St. Louis, Missouri 63130, United Sates.
authors: Robert E
authors: RE
authors: Blankenship
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002338:Carotenoids / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D002851:Chromatography, High Pressure Liquid; D003432:Cross-Linking Reagents / Q000737:chemistry; D019281:Dimerization; D008024:Ligands; D008027:Light; D008958:Models, Molecular; D008970:Molecular Weight; D010449:Peptide Mapping; D055668:Photochemical Processes; D058849:Protein Refolding / Q000528:radiation effects; D017434:Protein Structure, Tertiary / Q000528:radiation effects; D046939:Synechocystis / Q000378:metabolism*; D053719:Tandem Mass Spectrometry
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D008024:Ligands; C109473:orange carotenoid protein, Synechocystis; D002338:Carotenoids