Fig. 4. Mapping of Lhcb4.2 crosslinks putatively responsible for the structural anchor of paired PSII–LHCIIsc.

a Side-view of the (C₂S₂M)x2 fitted in the cryo-EM map EMD-3825, with the “knot” connecting density highlighted in red. b Enlarged view highlighting the inter-protein crosslinks involving the N-terminus (Arg1–Asp27) and the long hairpin (Pro42–Phe87) of Lhcb4.2. These two regions of the N-terminal loop of the Lhcb4.2 are shown in black in the inset. Side-view c and end-view d of the putative site of interaction between the flexible N-termini (Arg1–Asp27) of two Lhcb4.2 subunits facing from adjacent supercomplexes are shown, and their ~18 Å displacement from the “knot” density is indicated. Crosslinks within the distance cut-off of 17 Å for EDC (blue lines) and of 33 Å for DSSO (orange lines), and DSSO self-links (orange-black dashed lines) are shown. Subunits are coloured as follows: Lhcb2 in cyan; Lhcb4.2 in red; PsbH in green and CP47 in grey. Subunits not involved in crosslinks are left transparent.