Lutein Can Act as a Switchable Charge Transfer Quencher in the CP26 Light-harvesting Complex

Graham R. Fleming,Matteo Ballottari,Tae Kyu Ahn,Krishna K. Niyogi,Thomas J. Avenson,Roberto Bassi

doi:10.1074/jbc.m807192200

Graham R. Fleming, Matteo Ballottari + Show 4 more

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https://doi.org/10.1074/jbc.m807192200

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Abstract

Energy-dependent quenching of excitons in photosystem II of plants, or qE, has been positively correlated with the transient production of carotenoid radical cation species. Zeaxanthin was shown to be the donor species in the CP29 antenna complex. We report transient absorbance analyses of CP24 and CP26 complexes that bind lutein and zeaxanthin in the L1 and L2 domains, respectively. For CP24 complexes, the transient absorbance difference profiles give a reconstructed transient absorbance spectrum with a single peak centered at approximately 980 nm, consistent with zeaxanthin radical cation formation. In contrast, CP26 gives constants for the decay components probed at 940 and 980 nm of 144 and 194 ps, a transient absorbance spectrum that has a main peak at 980 nm, and a substantial shoulder at 940 nm. This suggests the presence of two charge transfer quenching sites in CP26 involving zeaxanthin radical cation and lutein radical cation species. We also show that lutein radical cation formation in CP26 is dependent on binding of zeaxanthin to the L2 domain, implying that zeaxanthin acts as an allosteric effector of charge transfer quenching involving lutein in the L1 domain.

Highlights

Regulation of light capture during photosynthesis occurs primarily within the antenna of photosystem II, the peripheral portion of which is comprised of trimeric light-harvesting complex (LHC) II4 [1] and the monomeric minor LHCs CP24, CP26, and CP29 [2]
We show that lutein radical cation formation in CP26 is dependent on binding of zeaxanthin to the L2 domain, implying that zeaxanthin acts as an allosteric effector of charge transfer quenching involving lutein in the L1 domain
We describe transient absorbance (TA) analyses of CP24 and CP26 complexes with various Cars bound to sites L1 and L2 by excitation of the complexes at the Chl Qy transition and probing for transient species within the near infrared region (NIR), as in Refs. 17–19

Summary

Introduction

Regulation of light capture during photosynthesis occurs primarily within the antenna of photosystem II, the peripheral portion of which is comprised of trimeric light-harvesting complex (LHC) II4 [1] and the monomeric minor LHCs CP24, CP26, and CP29 [2]. It was recently shown that excitation energy transfer from singlet-excited chlorophyll (Chl) to the S1 state of lutein (Lut) occurs both within isolated LHCII trimeric complexes [13], previously hypothesized to be a site for qE [14], and in vivo in a qE-dependent manner [13]. Chls a that bind to sites A5 and B5 (corresponding to Chl 5 and Chl 12, respectively, in LHCII [14]) are excitonically coupled [20], their interaction has been shown to be necessary for regulation of fluorescence lifetime [22, 23] and Chl triplet quenching in the homologous protein Lhca4 [24], and they have been shown to be involved in CT quenching in a (Chl-Z) complex within the L2 domain [19]. Lut is bound at the L1 site, which holds a pair of Chl binding sites (A2 and B2 corresponding to Chl 2 and Chl 7, respectively in LHCII [14]), both close to the Car and to each other [25], the features found for the L2 site and Chls A5 and B5 in CP29 [19]

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