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arXiv · 2405.14579

Assessment of S* in the Orange Carotenoid Protein

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

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.

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James P. Pidgeon, George A. Sutherland, Matthew S. Proctor, Shuangqing Wang, Dimitri Chekulaev, Sayantan Bhattacharya, Rahul Jayaprakash, Andrew Hitchcock, Ravi Kumar Venkatraman, Matthew P. Johnson, C. Neil Hunter, Jenny Clark. 2026-04-17. Assessment of S* in the Orange Carotenoid Protein. https://arxiv.org/abs/2405.14579

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