Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1847, Issue 10, Pages 1044-1054Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbabio.2015.05.010
Keywords
Carotenoid; Raman spectroscopy; Biophysics; Photoprotection; Density functional theory; Orange carotenoid protein (OCP)
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Funding
- European Research Council (ERC) through the Advanced Grant PHOTPROT [267333]
- French Agence Nationale de la Recherche (ANR) through contract CYANOPROTECT (Blanc SVSE 8)
- French Infrastructure for Integrated Structural Biology (FRISBI) [ANR-10-INSB-05-01]
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Orange carotenoid protein (OCP) is a cyanobacterial photoactive protein which binds echinenone as a chromophore; it is involved in photoprotection of these photosynthetic organisms against intense illumination. In its resting state, OCP appears orange (OCPo), and turns into a red form (OCPr) when exposed to blue-green light. Here we have combined resonance Raman spectroscopy and molecular modeling to investigate the mechanisms underlying the electronic absorption properties of the different forms of OCP. Our results show that there are at least two carotenoid configurations in the OCPo, suggesting that it is quite flexible, and that the OCPo to OCPr transition must involve an increase of the apparent conjugation length of the bound echinenone. Resonance Raman indicates that this chromophore must be in an all-trans configuration in OCPo. Density functional theory (DFT) calculations, in agreement with the Raman spectra of both OCP forms, show that the OCPo to OCPr transition must involve either an echinenone s-cis to s-trans isomerization which would affect the position of its conjugated end-chain rings, or a bending of the echinenone rings which would bring them from out of the plane of the C=C conjugated plane in the OCPo form into the C=C plane in the OCPr form. (C) 2015 Elsevier B.V. All rights reserved.
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