How paired PSII–LHCII supercomplexes mediate the stacking of plant thylakoid membranes unveiled by structural mass-spectrometry

Abstract

Grana are a characteristic feature of higher plants’ thylakoid membranes, consisting of stacks of appressed membranes enriched in Photosystem II (PSII) and associated light-harvesting complex II (LHCII) proteins, together forming the PSII-LHCII supercomplex. Grana stacks undergo light-dependent structural changes, mainly by reorganizing the supramolecular structure of PSII-LHCII supercomplexes. LHCII is vital for grana formation, in which also PSII-LHCII supercomplexes are involved. By combining top-down and crosslinking mass spectrometry we uncover the spatial organization of paired PSII-LHCII supercomplexes within thylakoid membranes. The resulting model highlights a basic molecular mechanism whereby plants maintain grana stacking at changing light conditions. This mechanism relies on interactions between stroma-exposed N-terminal loops of LHCII trimers and Lhcb4 subunits facing each other in adjacent membranes. The combination of light-dependent LHCII N-terminal trimming and extensive N-terminal α-acetylation likely affects interactions between pairs of PSII-LHCII supercomplexes across the stromal gap, ultimately mediating membrane folding in grana stacks.

Multimeric and monomeric photosystem II supercomplexes represent structural adaptations to low- and high-light conditions

“…S4), which has never been reported before (hereafter referred to as 'PSII-LHCII arraycomplexes'). In the other literature, similar bands to the A4 and A5 bands have been isolated by using α-DDM and these bands were identified as (C 2 S 2 ) 4 and (C 2 S 2 M 2 ) 2 formed by 'sandwiched' PSII-LHCII supercomplexes (23,24). However, these sandwiched complexes were absent in the isolation using amphipol (20,25).…”

“…The details of the molecular mechanism of how this configurational change occurs remains to be investigated by structural and ultrafast spectroscopic studies. Determination of the atomic structures of the multimeric complexes described here would be also important to discuss by comparing the LHCII heterogeneity reported recently (24).…”

Selective cross-linking of coinciding protein assemblies by in-gel cross-linking mass-spectrometry

“…After (tryptic) digestion, cross-linked peptides are subjected to various pre-fractionation steps or enrichment strategies, to distinguish them from the vast majority of unmodified peptides. Cross-linked residues are eventually identified using dedicated XL-MS search algorithms, providing structural information in the form of distance restraints, which can be utilized to guide computational homology modeling, refinement of flexible regions within structural models, protein-protein docking and the generation of protein interaction networks (Albanese et al, 2020;Bullock et al, 2018;Iacobucci et al, 2019;Kim et al, 2018;Ryl et al, 2020). Currently, technological developments in XL-MS aim to further improve the cross-linking reaction efficiency and detection.…”

Regulation of light harvesting in multimeric and monomeric photosystem II supercomplexes

“…S4), which has never been reported before (hereafter referred to as 'PSII-LHCII arraycomplexes'). In the other literature, similar bands with A4 and A5 bands have been isolated by using α-DDM and these bands were identified as (C 2 S 2 ) 4 and (C 2 S 2 M 2 ) 2 formed by 'sandwiched' PSII-LHCII supercomplexes (22,24). However, these sandwiched complexes were absent in the isolation using amphipol (20,25).…”