Photoprotection in Plants Involves a Change in Lutein 1 Binding Domain in the Major Light-harvesting Complex of Photosystem II

Andrew A Pascal,Bruno Robert,Pen-Nan Liao,Rienk Van Grondelle,Alexander V Ruban,Matthew P Johnson,Cristian Ilioaia,Peter J Walla

doi:10.1074/jbc.m111.234617

Abstract

Nonphotochemical quenching (NPQ) is the fundamental process by which plants exposed to high light intensities dissipate the potentially harmful excess energy as heat. Recently, it has been shown that efficient energy dissipation can be induced in the major light-harvesting complexes of photosystem II (LHCII) in the absence of protein-protein interactions. Spectroscopic measurements on these samples (LHCII gels) in the quenched state revealed specific alterations in the absorption and circular dichroism bands assigned to neoxanthin and lutein 1 molecules. In this work, we investigate the changes in conformation of the pigments involved in NPQ using resonance Raman spectroscopy. By selective excitation we show that, as well as the twisting of neoxanthin that has been reported previously, the lutein 1 pigment also undergoes a significant change in conformation when LHCII switches to the energy dissipative state. Selective two-photon excitation of carotenoid (Car) dark states (Car S(1)) performed on LHCII gels shows that the extent of electronic interactions between Car S(1) and chlorophyll states correlates linearly with chlorophyll fluorescence quenching, as observed previously for isolated LHCII (aggregated versus trimeric) and whole plants (with versus without NPQ).

Highlights

Unit protein-cofactor complexes, photosystem I (PSI)3 and photosystem II (PSII), and the excitation energy is efficiently transferred to their reaction centers where photochemistry takes place
Holzwarth et al have suggested that Cars are not directly involved in qE [15]; rather, they propose that quenching in light-harvesting complexes of photosystem II (LHCII) aggregates involves the formation of a Chl-Chl charge transfer state, characterized by weak far-red fluorescence emission [16]
It was further proposed that qE may involve both quenching in LHCII aggregates and at a separate site involving the PSII core and minor antenna complexes [12]

Summary

Pigment composition of isolated LHCII

Trimeric LHCII was prepared from WT and npq Arabidopsis plants (see “Experimental Procedures”). The conformational change is revealed by resonance Raman spectroscopy, a powerful and selective vibrational technique that gives access to the fine structure of photosynthetic chromophores These conformational changes involve an alteration in Chl-protein interactions as well as in the planarity of the LHCII-bound neoxanthin (Neo) carotenoid. Using the Raman technique we have shown recently that the ⌬A525 absorption change in Arabidopsis thaliana leaves lacking zeaxanthin belongs to a red-shifted sub-population of violaxanthin molecules formed during NPQ [23]. Direct and formal evidence of such a conformational change was provided by resonance Raman spectroscopy This method revealed perturbation in the environments of Neo and Chl b, two chromophores that are not directly involved in the process of energy quenching [9, 18, 25].

EXPERIMENTAL PROCEDURES

RESULTS

Funq Fq

DISCUSSION