Fig. 4

N. vectensis opsins have high levels of sequence diversity at canonically conserved functional sites. A Left, cartoon bovine rhodopsin structure showing 7 transmembrane domains surrounding the vitamin A derived chromophore and the highly conserved lysine at position 296 (black) required for chromophore binding. The glutamic acid counterion (orange) is conserved among vertebrate c-opsins and important for chromophore binding. Right, cartoon diagram of bovine rhodopsin sequence with select functional sites color coded by functional category, matching the numbered sites in B. Cartoon G protein subunits are shown bound to rhodopsin. The specific G protein alpha subunit can vary (letters in parentheses) depending on opsin sequence, with functional implications for type of signaling cascade activated. B Left, maximum-likelihood phylogeny of N. vectensis opsins, with IQtree2 support. Right, select N. vectensis opsin amino acids are aligned with bovine rhodopsin (c-opsin), D. melanogaster r-opsin, and T. cystophora cnidopsin. Canonically conserved functional residues and positions follow bovine rhodopsin numbering and correspond to A. From left to right, the first box contains structural features minimally required for function in all opsins. 7TM indicates protein sequence has seven transmembrane domains. Black is the conserved Lys(K)296; yellow shows conserved cysteine residues that form a stabilizing disulfide bridge. Second box lists known counterions from bilaterian and box jelly opsins (orange). Third box shows a conserved spectral tuning site across opsin clades (blue). A second spectral tuning site is also found at counterion site Asp(D)83. Substitutions known to cause a blue shift in both sites are shaded blue. Fourth box contains conserved sites known to be important for G-protein signaling (light gray). NvOpsin residues that are conserved at the known functional sites are shaded in dark gray. Rightmost, NvOpsins are labeled by subclade within each major anthozoan opsin clade