title: Photoactivation and relaxation studies on the cyanobacterial orange carotenoid protein in the presence of copper ion.
abstract: Photosynthesis starts with absorption of light energy by light-harvesting antenna complexes with subsequent production of energy-rich organic compounds. However, all photosynthetic organisms face the challenge of excess photochemical conversion capacity. In cyanobacteria, non-photochemical quenching (NPQ) performed by the orange carotenoid protein (OCP) is one of the most important mechanisms to regulate the light energy captured by light-harvesting antennas. This regulation permits the cell to meet its cellular energy requirements and at the same time protects the photosynthetic apparatus under fluctuating light conditions. Several reports have revealed that thermal dissipation increases under excess copper in plants. To explore the effects and mechanisms of copper on cyanobacteria NPQ, photoactivation and relaxation of OCP in the presence of copper were examined in this communication. When OCPo(OCP at orange state) is converted into OCPr(OCP at red state), copper ion has no effect on the photoactivation kinetics. Relaxation of OCPrto OCPo, however, is largely delayed-almost completely blocked, in the presence of copper. Even the addition of the fluorescence recovery protein (FRP) cannot activate the relaxation process. Native polyacrylamide gel electrophoresis (PAGE) analysis result indicates the heterogeneous population of Cu2+-locked OCPr. The Cu2+-OCP binding constant was estimated using a hyperbolic binding curve. Functional roles of copper-binding OCP in vivo are discussed.
authors.affiliation: Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO, 63130, USA.|Department of Biology, Washington University in St. Louis, St. Louis, MO, 63130, USA.
authors.forename: Haijun
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Washington University in St. Louis, St. Louis, MO, 63130, USA.|Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO, 63130, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO, 63130, USA.|Department of Biology, Washington University in St. Louis, St. Louis, MO, 63130, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Wolf
authors.affiliation: Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO, 63130, USA.|Department of Biology, Washington University in St. Louis, St. Louis, MO, 63130, USA.
authors.forename: Rafael
authors.initials: R
authors.lastname: Saer
authors.affiliation: Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO, 63130, USA.|Department of Biology, Washington University in St. Louis, St. Louis, MO, 63130, USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: King
authors.affiliation: Department of Chemistry, Washington University in St. Louis, St. Louis, MO, 63130, USA. blankenship@wustl.edu.|Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO, 63130, USA. blankenship@wustl.edu.|Department of Biology, Washington University in St. Louis, St. Louis, MO, 63130, USA. blankenship@wustl.edu.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Blankenship
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology*; D036681:Fluorescence Recovery After Photobleaching; D007477:Ions; D007700:Kinetics; D008027:Light; D046939:Synechocystis / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D001426:Bacterial Proteins; D007477:Ions; C109473:orange carotenoid protein, Synechocystis; D003300:Copper
keywords: Copper; Orange carotenoid protein; Photoprotection; Photosynthesis