4

1,2

Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). We found evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a delocalized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can "tune" the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophyll-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

¹ Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
² Department of Chemistry and QB3 Institute, University of California, Berkeley, CA 94720, USA.
³ Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720, USA.
⁴ Department of Science and Technology, University of Verona, 37134 Verona, Italy.

^* These authors contributed equally to this work.

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