Structural Determinats Underlying Photoprotection in the Photoactive Orange Carotenoid Protein of Cyanobacteria Page: 1 of 27
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STRUCTURAL DETERMINANTS UNDERLYING PHOTOPROTECTION IN THE
PHOTOACTIVE ORANGE CAROTENOID PROTEIN OF CYANOBACTERIA
Adjele Wilson",2, James N. Kinney3, Petrus H. Zwart3, Claire Punginellii,2, Sandrine D'Haene12,
Franeois Perreau4, Michael G. Klein3, Diana Kirilovsky1,2 and Cheryl A. Kerfeld3,5
From Commissariat i l'Energie Atomique (CEA), Institut de Biologie et Technologies de Saclay
(iBiTec-S) 1 and Centre National de la Recherche Scientifique (CNRS), URA 2906, 91191 Gif sur
Yvette, France,2 United States Department of Energy - Joint Genome Institute, Walnut Creek CA
94598,3 Institut Jean-Pierre Bourgin, UNR 1318 INRA-AgroParisTech, INRA Versailles-
Grignon, Route de Saint Cyr, F-78026 Versailles, France4
and Department of Plant and Microbial Biology, University of California, Berkeley, CA 947205
Address correspondence to: Cheryl Kerfeld UCB/JGI, 2800 Mitchell Drive, Walnut Creek, CA 94598.
Tel.: 925-296-5691; FAX 925-296-5752; E-mail: ckerfeldkberkeley.edu
Running title: Structural Insights into Cyanobacterial Photoprotection
The photoprotective processes of
photosynthetic organisms involve the
dissipation of excess absorbed light energy
as heat. Photoprotection in cyanobacteria is
mechanistically distinct from that in plants;
it involves the Orange Carotenoid Protein
(OCP), a water-soluble protein containing a
single carotenoid. The OCP is a new
member of the family of blue light
photoactive proteins; blue-green light
triggers the OCP-mediated photoprotective
response. Here we report structural and
functional characterization of the wildtype
and two mutant forms of the OCP, from the
model organism Synechocystis PCC6803.
The structural analysis provides high
resolution detail of the carotenoid-
protein interactions that underlie the
optical properties of the OCP, unique
among carotenoid-proteins in binding a
single pigment per polypeptide chain.
Collectively, these data implicate several
key amino acids in the function of the
OCP and reveal that the
photoconversion and photoprotective
responses of the OCP to blue-green light
can be decoupled.
The capture of light energy for oxygenic
photosynthesis is arguably one of the most
important metabolic processes on earth. It is
also inherently risky; the absorbance of excess
light energy beyond what can be used in
photosynthesis can result in photooxidative
damage to the organism. Consequently,
photosynthetic organisms have evolved
protective mechanisms to dissipate excess
captured energy. In plants, one of these
mechanisms involves the membrane-embedded
chl antenna of Photosystem II (PSII), the
Light-Harvesting-Complex (LHCII) (for
reviews, see (1-4). Under saturating light
conditions, the decrease of the lumen pH
activates the xanthophyll cycle (5,6) and the
protonation of PsbS, a PSII subunit (7).
Conformational changes in the LHCII,
modifying the interaction between chlorophyll
molecules and carotenoids and allowing
thermal dissipation, are also involved in this
mechanism (8-10). Energy dissipation is
accompanied by a diminution of PSII related
fluorescence emission, also known as non-
photochemical-quenching (NPQ; more
specifically qE) which usually serves as a
measure of the dissipation process.
While the photoprotective mechanism
of plants is well studied, only recently have
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Wilson, Adjele; Kinney, James N.; Zwart, Petrus H.; Punginelli, Claire; D'Haene, Sandrine; Perreau, Francois et al. Structural Determinats Underlying Photoprotection in the Photoactive Orange Carotenoid Protein of Cyanobacteria, article, April 1, 2010; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc1012404/m1/1/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.