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Publication Abstract from PubMed

Orange Carotenoid protein (OCP) is the only known photoreceptor which uses carotenoid for its activation. It is found exclusively in cyanobacteria, where it functions to control light-harvesting of the photosynthetic machinery. However, the photochemical reactions and structural dynamics of this unique photosensing process are not yet resolved. We present time-resolved crystal structures at second-to-minute delays under bright illumination, capturing the early photoproduct and structures of the subsequent reaction intermediates. The first stable photoproduct shows concerted isomerization of C9'-C8' and C7'-C6' single bonds in the bicycle-pedal (s-BP) manner and structural changes in the N-terminal domain with minute timescale kinetics. These are followed by a thermally-driven recovery of the s-BP isomer to the dark state carotenoid configuration. Structural changes propagate to the C-terminal domain, resulting, at later time, in the H-bond rupture of the carotenoid keto group with protein residues. Solution FTIR and UV/Vis spectroscopy support the single bond isomerization of the carotenoid in the s-BP manner and subsequent thermal structural reactions as the basis of OCP photoreception.

Light activation of Orange Carotenoid Protein reveals bicycle-pedal single-bond isomerization.,Chukhutsina VU, Baxter JM, Fadini A, Morgan RM, Pope MA, Maghlaoui K, Orr CM, Wagner A, van Thor JJ Nat Commun. 2022 Oct 28;13(1):6420. doi: 10.1038/s41467-022-34137-4. PMID:36307413^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.