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Scientific result | Photosynthesis

The molecular evolution of the Orange Carotenoid Protein finally elucidated!

​A new phylogenetic analysis of the Orange Carotenoid Proteins (OCPs) family, responsible for photoprotection in cyanobacteria, coupled with a functional study, was conducted by a team from I2BC@Saclay. This is the first functional study of the ancestral OCPX which, when compared to OCP1 and OCP2, revealed the molecular determinants that govern the photocycle of these proteins and in particular the fundamental role of the linker connecting the two domains of OCPs.

Published on 4 October 2019


The photoactive orange carotenoid protein (OCP) is a blue-light intensity sensor involved in cyanobacterial photoprotection. Three OCP families co-exist (OCPX, OCP1 and OCP2), having originated from the fusion of ancestral domain genes. Here, we report the characterization of an OCPX and the evolutionary characterization of OCP paralogues focusing on the role of the linker connecting the domains. The addition of the linker with specific amino acids enabled the photocycle of the OCP ancestor. OCPX is the paralogue closest to this ancestor. A second diversification gave rise to OCP1 and OCP2. OCPX and OCP2 present fast deactivation and weak antenna interaction. In OCP1, OCP deactivation became slower and interaction with the antenna became stronger, requiring a further protein to detach OCP from the antenna and accelerate its deactivation. OCP2 lost the tendency to dimerize, unlike OCPX and OCP1, and the role of its linker is slightly different, giving less controlled photoactivation.

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