Paper

Assessment of S in the Orange Carotenoid Protein

Pidgeon, James P, Wang, Shuangqing, Proctor, Matthew S, Bhattacharya, Sayantan, Venkatraman, Ravi Kumar, Hunter, C Neil, Hitchcock, Andrew, Clark, Jenny, Jayaprakash, Rahul, Johnson, Matthew P, Sutherland, George A, Chekulaev, Dimitri

2026

Overview

The orange carotenoid protein (OCP) is the water-soluble mediator of non-photochemical quenching in cyanobacteria, a crucial photoprotective mechanism in response to excess illumination. OCP converts from a dark-adapted inactive state (OCPo) to an active quenching conformation (OCPr) under high-light conditions, resulting in a concomitant redshift in the absorption of the bound carotenoid. Here, we test whether a long-lived carotenoid singlet excited state (S*) is required for this photoconversion. We measured pump wavelength-dependent transient absorption of OCPo trapped in trehalose-sucrose glass films. We found that initial OCP photoproducts are still formed despite the glass preventing completion to OCPr, and that S* is only apparent for <495 nm pumps. By comparison to the pump wavelength-dependence of the OCPo to OCPr conversion in buffer, we show that S* is not required for photoconversion, and that S* likely arises from ground-state heterogeneity within OCPo.

• Publisher: Cornell University Library, arXiv.org
• Subject: Absorption / Carotenoids / Cyanobacteria / Darkness / Heterogeneity / Illumination / Optical properties / Proteins / Red shift / Room temperature / Trehalose