Figure 1: The PSII RC complex (PDB: 3wu2).
From: A single residue controls electron transfer gating in photosynthetic reaction centers
(a) The four-helix bundle includes helices d1, e1, d2, e2 of the D1 (green) and D2 (purple) subunits. It holds a central cluster of chlorophylls (P680), including a central pair (green) flanked by additional Chls (yellow), Phe (purple), quinones (red) and the non-heme iron (red sphere), that is further ligated by a bicarbonate (red). See Supplemental Fig. 1 for a depiction of all the 10 TM helices of subunits D1 and D2. Within the four-helix bundle, intersubunit interactions are found at the center of d1 (D1-208 and D1-209) and d2 helices, around the non-heme iron, where histidines (black) from the two subunits ligate an iron ion, and at the central P680 Chls, where histidines from the two subunits ligate the Mg ions. A 90o turn (bottom) shows that the d helices form an ‘X’ shape with D1-208 at their center. (b) The intersubunit Cα-Cα distances between of the studied GxxxG-like motifs: D1 residues Gly208, Ala209, and Cys212 and their closest D2 residues Ala208, Gly207 and Cys211, respectively. The histidines ligating the non-heme iron (red sphere) and central P680 Chls (green) are depicted. (c) The intersubunit Cα-Cα distances (y-axis) between d1 (x-axis) and the closest Cα on d2 (see Supplementary Fig. 1, for detailed table). (d) The list of residues enabling photoautotrophic growth for the three studied amino acids includes 4 residues for D1-208, 9 for D1-209 and 14 for D1-212.
