Characterization of the Synechocystis PCC 6803 Fluorescence Recovery Protein involved in photoprotection

Abstract

Under high irradiance, most cyanobacteria induce a photoprotective mechanism that decreases the energy arriving at the photosynthetic reaction centers to avoid the formation of dangerous species of oxygen. This mechanism which rapidly increases the heat dissipation of excess energy at the level of the cyanobacterial antenna, the phycobilisomes, is triggered by the photoactivation of the Orange Carotenoid Protein (OCP). Under low light conditions, the Fluorescence Recovery Protein (FRP) mediates the recovery of the full antenna capacity by accelerating the deactivation of the OCP. Several FRP Synechocystis mutants were constructed and characterized in terms of the OCP-related photoprotective mechanism. Our results demonstrate that Synechocystis FRP starts at Met26 and not at Met1 (according to notation in Cyanobase) as was previously suggested. Moreover, changes in the genomic region upstream the ATG encoding for Met26 influenced the concentration of OCP in cells. A long FRP (beginning at Met1) is synthesized in Synechocystis cells when the frp gene is under the control of the psbA2 promoter but it is less active than the shorter protein. Overexpression of the short frp gene in Synechocystis enabled short FRP isolation from the soluble fraction. However, the high concentration of FRP in this mutant inhibited the induction of the photoprotective mechanism by decreasing the concentration of the activated OCP. Therefore, the amplitude of photoprotection depends on not only OCP concentration but also on that of FRP. The synthesis of FRP and OCP must be strictly regulated to maintain a low FRP to OCP ratio to allow efficient photoprotection.

Structural rearrangements in the C-terminal domain homolog of Orange Carotenoid Protein are crucial for carotenoid transfer

“…Cyanobacteria have evolved several protection mechanisms including non-photochemical quenching, induced by the Orange Carotenoid Protein (OCP) 4,5 . OCP is a water-soluble, carotenoid-binding, 35 kDa protein found to induce dissipation of phycobilisome excitation energy minimizing energy flux toward the reaction centers 5–7 . OCP can also directly protect against the presence of singlet oxygen 8,9 .…”

Paralogs of the C-Terminal Domain of the Cyanobacterial Orange Carotenoid Protein Are Carotenoid Donors to Helical Carotenoid Proteins

“…FRP activity is independent of light: it is active in the dark but also under high-light conditions Thurotte et al, 2017). FRP affinity to OCP r is strong, and its presence during illumination decreases the amplitude of OCP-triggered PBS fluorescence quenching by accelerating the OCP r -to-OCP o conversion (Gwizdala et al, 2011(Gwizdala et al, , 2013Kuzminov et al, 2012;Sluchanko et al, 2017;Thurotte et al, 2017) and maybe also by interacting with OCP o (with low affinity) and preventing its photoactivation . FRP is present mostly as a dimer in solution (Sutter et al, 2013;Lu et al, 2017;Sluchanko et al, 2017).…”

O2-dependent large electron flow functioned as an electron sink, replacing the steady-state electron flux in photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803, but not in the cyanobacterium Synechococcus sp. PCC 7942

“…A deficiency of the OCP protein in the S. 6803 mutant suppresses the NPQ of Chl fluorescence. [3][4][5] This mutant also suffers from photoinhibition of PSII as compared to wild-type S. 6803. [3][4][5] Furthermore, OCPdependent dissipation of excess photon energy shows species dependency in cyanobacteria.…”

“…PCC 7942 (S. 7942) does not have a gene coding for OCP and does not show any OCP-dependent NPQ of Chl fluorescence. [3][4][5] In the second part, the light-harvesting capacity of PSI and PSII is regulated by the state transition, 6) a rapid change in configuration of the light-harvesting machinery from state I (or II) to state II (or I). State I is induced when PSI is photoexcited more than PSII.…”

“…[3][4][5] Orange carotenoid protein (OCP) is bound to phycobilisomes and absorbs photon energy from the phycobilisome. Excited OCP then returns to the ground state following heat dissipation that can be observed as nonphotochemical quenching (NPQ) of chlorophyll (Chl) fluorescence.…”