Fig. 8.
a Structural overlap of the D2 protein of Photosystem II (gray) and the last five transmembrane helices of the PsaB subunit of Photosystem I (orange). The amino acids that are strictly conserved are shown in sticks, and the corresponding sequence numbers are given according to the crystal structures 3ARC (Photosystem II) and 1JB0 (Photosystem I). b Position of the special pair pigment PB and PD2 relative to the tenth and fourth transmembrane helices of PsaB and D2, respectively. The question mark highlights two residues that could be homologous but occupy different structural positions