In this study, we analyzed multibilayer lipid-protein membranes composed of the photosynthetic light-harvesting complex II (LHCII; isolated from spinach [Spinacia oleracea]) and the plant lipids monogalcatosyldiacylglycerol and digalactosyldiacylglycerol. Two types of pigment-protein complexes were analyzed: those isolated from dark-adapted leaves (LHCII) and those from leaves preilluminated with high-intensity light (LHCII-HL). The LHCII-HL complexes were found to be partially phosphorylated and contained zeaxanthin. The results of the x-ray diffraction, infrared imaging microscopy, confocal laser scanning microscopy, and transmission electron microscopy revealed that lipid-LHCII membranes assemble into planar multibilayers, in contrast with the lipid-LHCII-HL membranes, which form less ordered structures. In both systems, the protein formed supramolecular structures. In the case of LHCII-HL, these structures spanned the multibilayer membranes and were perpendicular to the membrane plane, whereas in LHCII, the structures were lamellar and within the plane of the membranes. Lamellar aggregates of LHCII-HL have been shown, by fluorescence lifetime imaging microscopy, to be particularly active in excitation energy quenching. Both types of structures were stabilized by intermolecular hydrogen bonds. We conclude that the formation of trans-layer, rivet-like structures of LHCII is an important determinant underlying the spontaneous formation and stabilization of the thylakoid grana structures, since the lamellar aggregates are well suited to dissipate excess energy upon overexcitation.

The effects of 50 μM cadmium (Cd) or copper (Cu) ions on the supramolecular conformation of the light-harvesting pigment–protein complex of PSII (LHCII) isolated from rye seedlings were studied. It was found that the action of these two metal ions on the LHCII structure and organization is dissimilar. The Fourier transform infrared (FTIR) measurements indicated inhibition or stimulation of formation of parallel β-structures and aggregates in the presence of Cd or Cu ions, respectively. The Chl a fluorescence excitation spectra of LHCII extracted from Cd-treated plants showed that the decreased aggregation of complexes was correlated with a decline in efficiency of quenching of excitation energy. From the results of mass spectrometry, changes in LHCII aggregation in the presence of Cd ions might be based on decreases in the molecular mass of Lhcb1 and Lhcb2 proteins. An increase in the content of LHCII aggregates under Cu ion excess was associated with changes in the LHCII xanthophyll pigment pool. In the complexes isolated from Cu-treated plants, all-trans violaxanthin and 9′-cis neoxanthin content declined and the simultaneous appearance of the fraction of 9-cis violaxanthin was observed. 9-cis violaxanthin formation under Cu ion excess might facilitate LHCII inter-trimer interaction and, therefore, aggregation of complexes. RLS (resonance light scattering) spectra indicated that the excitonic interaction between Chl molecules and between Chls and xanthophylls was responsible for the effective dissipation of excitation energy in LHCII isolated from Cu-treated plants. Also, changes in singlet excitation energy transfer between carotenoids and Chls under the action of heavy metals were observed.