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J. Biol. Chem., Vol. 283, Issue 10, 6184-6192, March 7, 2008

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Photoprotection in the Antenna Complexes of Photosystem II

ROLE OF INDIVIDUAL XANTHOPHYLLS IN CHLOROPHYLL TRIPLET QUENCHING^*

Milena Mozzo, Luca Dall'Osto^¶, Rainer Hienerwadel^||, Roberto Bassi^¶, and Roberta Croce¹

From the Department of Biophysical Chemistry, Groningen Bimolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, Istituto di Biofisica del Consiglio Nazionale delle Ricerche, via Sommarive 18, 38100 Povo-Trento, Italy, ^¶Dipartimento Scientifico e Tecnologico, Università di Verona, Strada Le Grazie 15-37134 Verona, Italy, and ^||Université d'Aix-Marseille II, LGBP-Département de Biologie, Faculté de Sciences de Luminy, 163 Avenue de Luminy, 13288 Marseille, France

In this work the photoprotective role of all xanthophylls in LHCII, Lhcb4, and Lhcb5 is investigated by laser-induced Triplet-minus-Singlet (TmS) spectroscopy. The comparison of native LHCII trimeric complexes with different carotenoid composition shows that the xanthophylls in sites V1 and N1 do not directly contribute to the chlorophyll triplet quenching. The largest part of the triplets is quenched by the lutein bound in site L1, which is located in close proximity to the chlorophylls responsible for the low energy state of the complex. The lutein in the L2 site is also active in triplet quenching, and it shows a longer triplet lifetime than the lutein in the L1 site. This lifetime difference depends on the occupancy of the N1 binding site, where neoxanthin acts as an oxygen barrier, limiting the access of O₂ to the inner domain of the Lhc complex, thereby strongly contributing to the photostability. The carotenoid triplet decay of monomeric Lhcb1, Lhcb4, and Lhcb5 is mono-exponential, with shorter lifetimes than observed for trimeric LHCII, suggesting that their inner domains are more accessible for O₂. As for trimeric LHCII, only the xanthophylls in sites L1 and L2 are active in triplet quenching. Although the chlorophyll to carotenoid triplet transfer is efficient (95%) in all complexes, it is not perfect, leaving 5% of the chlorophyll triplets unquenched. This effect appears to be intrinsically related to the molecular organization of the Lhcb proteins.

Received for publication, October 31, 2007 , and in revised form, December 7, 2007.

^* This work was supported by the Netherlands Organization for Scientific Research, Earth and Life Science through a VIDI grant, European Union Grant MRTN-CT-2003-505069, Intro2, Provincia of Trento Grant SAMBAx2, and by the Fondo per gli Investimenti della Ricerca Italiana contract RBLA0345SF from the Italian basic research foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 31503634214; Fax: 31503634800; E-mail: R.Croce{at}rug.nl.

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