Oral and Poster Presentation 18th International Congress on Photobiology 2024

Light activation mechanism of Orange Carotenoid Protein resolved by femtosecond stimulated Raman Spectroscopy (#49)

Miroslav Kloz 1
  1. The Extreme Light Infrastructure ERIC, Dolní Břežany, CZECH REPUBLIC, Czech Republic

The Orange Carotenoid Protein (OCP) is a distinctive water-soluble keto-carotenoid binding protein primarily found in cyanobacteria, crucial for non-photochemical quenching—a protective mechanism dissipating excess absorbed light energy as heat, shielding photosynthetic organisms from photodamage. Upon photon absorption, hydrogen bonds within the carotenoid-protein complex break, transitioning OCP from its orange to red-absorbing form, enabling binding to Phycobilisome. The process's enigmatic nature stems from its exceptionally low quantum yield, likely a result of evolutionary adaptation to high light conditions. Employing steady-state and time-resolved spectroscopy, notably fs stimulated Raman spectroscopy, we systematically investigated the vibrational characteristics of optically excited echinenone in various solvents and OCP in both red and orange states. Our innovative technique, employing synchronized fs amplifiers and controlled pump pulse displacement, facilitated recording of OCP photoactivation dynamics from 70 fs to 10 ms, spanning a staggering 12 orders of temporal range in a single experiment. Our findings unveil a unique multiphoton activation pathway, suggesting OCP's light intensity sensing capability. While early photoproducts tend to revert to their original configuration, the probability is significantly altered upon receiving additional photons within a specific timeframe. Our coherent Raman experiment sheds light on the carotenoid's heat dissipation pathways within OCP, revealing distinct vibration bond excitation profiles compared to those observed in solution. This evidence supports the notion that OCP has evolved to control energy dissipation in carotenoids, directing it into the protein through controlled pathways, indicative of evolutionary adaptation.