Figure 7.

Conservation of FRL-PsbH residues. In (A), the Synechococcus 7335 apo-FRL-PSII structure (colored), the homology model of the FRL-PsbH ancestral sequence (white), and two non-FaRLiP holocomplex PSII structures (light and dark grey from T. vulcanus and Synechocystis 6803, respectively) are superimposed. Cartoons are shown with partial transparency and stick representations of applicable residues and cofactors are shown. For Chl molecules, only tetrapyrrole rings are shown. The Chl f assigned in PsbB of the Synechococcus 7335 apo-FRL-PSII structure is highlighted in red. The Chl a site that is suggested to bind Chl f in other species and the FRL-PSII ancestor is highlighted in orange. Additional views of the PsbH2 homology model can be found in Supplementary Figure S7. In (B), a partial sequence alignment is shown that includes the FRL-ancestral sequence and FRL- and VL-specific sequences from extant FaRLiP-capable cyanobacteria. Note that the sequence from Synechococcus 7335 is highlighted in grey to signify that there are presently no corresponding structural data on this subunit. Conserved FRL-specific residues in extant cyanobacteria are highlighted in dark grey in the sequence from Synechococcus 7335. If the same position is conserved in the FRL ancestral sequence, it is highlighted in yellow. Vertical lines above residue positions in (B) correspond to amino acids labeled in (A). The Clustal Omega sequence conservation identifiers are shown below the alignment.