The cyanobacterial Fluorescence Recovery Protein has two distinct activities: Orange Carotenoid Protein amino acids involved in FRP interaction

Abstract

To deal with fluctuating light condition, cyanobacteria have developed a photoprotective mechanism which, under high light conditions, decreases the energy arriving at the photochemical centers. It relies on a photoswitch, the Orange Carotenoid Protein (OCP). Once photoactivated, OCP binds to the light harvesting antenna, the phycobilisome (PBS), and triggers the thermal dissipation of the excess energy absorbed. Deactivation of the photoprotective mechanism requires the intervention of a third partner, the Fluorescence Recovery Protein (FRP). FRP by interacting with the photoactivated OCP accelerates its conversion to the non-active form and its detachment from the phycobilisome. We have studied the interaction of FRP with free and phycobilisome-bound OCP. Several OCP variants were constructed and characterized. In this article we show that OCP amino acid F299 is essential and D220 important for OCP deactivation mediated by FRP. Mutations of these amino acids did not affect FRP activity as helper to detach OCP from phycobilisomes. In addition, while mutated R60L FRP is inactive on OCP deactivation, its activity on the detachment of the OCP from the phycobilisomes is not affected. Thus, our results demonstrate that FRP has two distinct activities: it accelerates OCP detachment from phycobilisomes and then it helps deactivation of the OCP. They also suggest that different OCP and FRP amino acids could be involved in these two activities.

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

“…Less is known about the interaction of FRP with the bound OCP r . None of mutations tested until now have prevented the FRP-induced acceleration of OCP detachment from PBS (Thurotte et al, 2017).…”

“…FRP interacts with high affinity with the CTD of free and bound OCP r (Boulay et al, 2010;Sutter et al, 2013). In in vitro experiments, the presence of FRP accelerates the OCP r -to-OCP o conversion (Boulay et al, 2010;Sutter et al, 2013;Thurotte et al, 2017) and the recovery of PBS fluorescence (Gwizdala et al, 2011;Thurotte et al, 2015Thurotte et al, , 2017. FRP activity is independent of light: it is active in the dark but also under high-light conditions Thurotte et al, 2017).…”

“…In in vitro experiments, the presence of FRP accelerates the OCP r -to-OCP o conversion (Boulay et al, 2010;Sutter et al, 2013;Thurotte et al, 2017) and the recovery of PBS fluorescence (Gwizdala et al, 2011;Thurotte et al, 2015Thurotte et al, , 2017. 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 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).…”

“…It was proposed that it could monomerize upon binding to CTD . FRP Arg-60 and OCP Phe-299 are essential for the activity of FRP in the conversion OCP r to OCP o (Thurotte et al, 2017). Less is known about the interaction of FRP with the bound OCP r .…”