Figure 4.

Amino acid alignment of opsin sequences. The four H. robusta opsins of each strain are compared to the ciliary rhodopsin from Bos taurus and the rhabdomeric opsin from Platynereis dumerilii. All opsins show seven transmembrane domains (TM I- VII) typical for G-protein coupled receptors, the protein family opsins belong to. Amino acids conserved throughout all opsins are highlighted in yellow. Amino acids essential for every functional visual opsin are marked in blue: The Glutamate (E) marked between transmembrane domain IV and V serves as counterion to stabilize the Schiffbase-linkage of the chromophore to the Lysine (K) located in domain VII. The motif SHP is marked with an asterisk which is distinctive for rhabdomeric opsins and distinguishes them from the ciliary opsins.