Probing the timescales of cyanobacterial photoprotection in vitro with the novel PHOTOactivation VISible Transient Absorption spectroscopy

Photosynthesis sustains life on Earth by turning sunlight into fuel for other biological processes. However, photosynthetic organisms can face a lethal threat when they suddenly receive too much light.

In cyanobacteria, key photoprotection against excessive illumination involves the Orange Carotenoid Protein (OCP) and the light-harvesting pigment-proteins, Phycobilisomes (PBs).

When photoactivated OCP binds to a PB, surplus solar energy absorbed by the PB is safely dissipated, and photosynthesis can continue despite dangerous conditions.

While our understanding of the OCP-related mechanism has improved over the last years, its dynamic aspects and the intermediate steps of activation remain largely elusive due to the lack of appropriate experimental techniques.

In this interdisciplinary project, I will explore the OCP-related mechanism in vitro using a novel spectroscopic approach: the PHOTOactivation VISible Transient Absorption spectroscopy (photoVISTA) and isolated OCPs & PBs.

With photoVISTA, I will dissect the activation of this molecular mechanism across multiple timescales with the femtosecond temporal resolution, from the earliest photophysical and photochemical reactions taking place at the order of femtoseconds to processes beyond the seconds.

I will reveal the intermediate steps between the initial absorption of a photon by the OCP and its photoactivation, up to its binding and docking on a PB and energy dissipation in the OCP-PB complex.

Being a multipulse technique, photoVISTA will provide unprecedented control over OCP’s photoactivation and will let me propose a comprehensive molecular model of photoprotection beyond the reach of conventional pump-probe spectroscopy.

The breakthroughs in this project, further explaining how cyanobacteria manage the flow of excitation energy in their photosynthetic apparatus, will give us crucial know-how for improving photosynthesis and impacting green biotechnology and food production.