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A more recent version of this article appeared on February 8, 2008
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M705645200v1
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Papers In Press, published online ahead of print November 8, 2007
J. Biol. Chem, 10.1074/jbc.M705645200
Submitted on July 10, 2007
Revised on November 7, 2007
Accepted on November 7, 2007

Zeaxanthin radical cation formation in minor light-harvesting complexes of higher plant antenna

Tom J. Avenson, Tae K. Ahn, Donatas Zigmantas, Kris K. Niyogi, Zhirong Li, Matteo Ballottari, Roberto Bassi, and Graham R. Fleming

Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720

Corresponding Author: GRFleming{at}lbl.gov

Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5% of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N)LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.


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T. K. Ahn, T. J. Avenson, M. Ballottari, Y.-C. Cheng, K. K. Niyogi, R. Bassi, and G. R. Fleming
Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein
Science, May 9, 2008; 320(5877): 794 - 797.
[Abstract] [Full Text] [PDF]

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G. Bonente, B. D. Howes, S. Caffarri, G. Smulevich, and R. Bassi
Interactions between the Photosystem II Subunit PsbS and Xanthophylls Studied in Vivo and in Vitro
J. Biol. Chem., March 28, 2008; 283(13): 8434 - 8445.
[Abstract] [Full Text] [PDF]


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