Lhcb6 (CP24) is a monomeric antenna protein of photosystem II, which has been shown to play special roles in photoprotective mechanisms, such as the Non-Photochemical Quenching and reorganization of grana membranes in excess light conditions. In this work we analyzed Lhcb6 in vivo and in vitro: we show this protein, upon activation of the xanthophyll cycle, accumulates zeaxanthin into inner binding sites faster and to a larger extent than any other pigment-protein complex. By comparative analysis of Lhcb6 complexes violaxanthin or zeaxanthin binding, we demonstrate that zeaxanthin not only down-regulates chlorophyll singlet excited states, but also increases the efficiency of chlorophyll triplet quenching, with consequent reduction of singlet oxygen production and significant enhancement of photo-stability. On these bases we propose that Lhcb6, the most recent addition to the Lhcb protein family which evolved concomitantly to the adaptation of photosynthesis to land environment, has a crucial role in zeaxanthin-dependent photoprotection.

Dynamics of zeaxanthin binding to the photosystem II monomeric antenna protein Lhcb6 (CP24) and modulation of its photoprotection properties.

BETTERLE, Nico;BALLOTTARI, Matteo;DALL'OSTO, Luca;BASSI, Roberto
2010

Abstract

Lhcb6 (CP24) is a monomeric antenna protein of photosystem II, which has been shown to play special roles in photoprotective mechanisms, such as the Non-Photochemical Quenching and reorganization of grana membranes in excess light conditions. In this work we analyzed Lhcb6 in vivo and in vitro: we show this protein, upon activation of the xanthophyll cycle, accumulates zeaxanthin into inner binding sites faster and to a larger extent than any other pigment-protein complex. By comparative analysis of Lhcb6 complexes violaxanthin or zeaxanthin binding, we demonstrate that zeaxanthin not only down-regulates chlorophyll singlet excited states, but also increases the efficiency of chlorophyll triplet quenching, with consequent reduction of singlet oxygen production and significant enhancement of photo-stability. On these bases we propose that Lhcb6, the most recent addition to the Lhcb protein family which evolved concomitantly to the adaptation of photosynthesis to land environment, has a crucial role in zeaxanthin-dependent photoprotection.
photoprotection; zeaxanthin; CP24; LHC
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11562/345583
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