The Cyanobacterial Photoactive Orange Carotenoid Protein Is an Excellent Singlet Oxygen Quencher  

Abstract

Cyanobacteria have developed a photoprotective mechanism that decreases the energy arriving at the photosynthetic reaction centers under high-light conditions. The photoactive orange carotenoid protein (OCP) is essential in this mechanism as a light sensor and energy quencher. When OCP is photoactivated by strong blue-green light, it is able to dissipate excess energy as heat by interacting with phycobilisomes. As a consequence, charge separation and recombination leading to the formation of singlet oxygen diminishes. Here, we demonstrate that OCP has another essential role. We observed that OCP also protects Synechocystis cells from strong orange-red light, a condition in which OCP is not photoactivated. We first showed that this photoprotection is related to a decrease of singlet oxygen concentration due to OCP action. Then, we demonstrated that, in vitro, OCP is a very good singlet oxygen quencher. By contrast, another carotenoid protein having a high similarity with the N-terminal domain of OCP is not more efficient as a singlet oxygen quencher than a protein without carotenoid. Although OCP is a soluble protein, it is able to quench the singlet oxygen generated in the thylakoid membranes. Thus, OCP has dual and complementary photoprotective functions as an energy quencher and a singlet oxygen quencher.

Fluorescent Labeling Preserving OCP Photoactivity Reveals Its Reorganization during the Photocycle

“…OCP acts as a blue-green light intensity sensor (5). In vivo under strong light, OCP is converted to its active signaling state, which interacts with phycobilisomes and quenches the excess of excitation energy (3,(6)(7)(8)(9), thereby decreasing the effective absorption cross section of the photosystems and preventing the formation of potentially damaging reactive oxygen species (10). The mechanism of NPQ and its regulation is still unclear due to the number and size of protein complexes involved.…”

Different Functions of the Paralogs to the N-Terminal Domain of the Orange Carotenoid Protein in the Cyanobacterium Anabaena sp. PCC 7120

“…The production of 1 O 2 was induced by illumination of methylene blue. The concentration of protein that decreased 50% the EPR signal (I 50 ) was about 1.2 to 1.5 mM for the Anabaena NTD-OCP and All3221, similar to Synechocystis OCP (Sedoud et al, 2014). A higher concentration was needed for the other NTD paralogs: 3 to 4 mM for Alr4873, 25 to 30 mM All4941, and more than 50 mM for All1123.…”

“…The 1 O 2 quenching activity of the NTD paralogs and of the Anabaena NTD-OCP was measured in vitro as described by Sedoud et al (2014). Electron paramagnetic resonance (EPR) spin trapping was applied for 1 O 2 detection using TEMPD-HCl (2,2,6,6-tetramethyl-4-piperidone).…”

“…The avid singlet oxygen quenching activity of the OCP and of the isolated OCP-NTD was first shown by Kerfeld and colleagues even before the involvement of the OCP in excitation energy quenching was discovered (Kerfeld et al, 2003). More recently, it was demonstrated the importance of this activity in cell photoprotection (Sedoud et al, 2014).…”

“…This reduces the amount of energy arriving at both reaction centers (Scott et al, 2006;Wilson et al, 2006;Rakhimberdieva et al, 2010;Gorbunov et al, 2011). The OCP has another photoprotective function, serving as an efficient quencher of singlet oxygen species (Kerfeld et al, 2003;Sedoud et al, 2014). The avid singlet oxygen quenching activity of the OCP and of the isolated OCP-NTD was first shown by Kerfeld and colleagues even before the involvement of the OCP in excitation energy quenching was discovered (Kerfeld et al, 2003).…”