Figure 1—figure supplement 3. Alignment of major opsin clades showing conserved lysine in transmembrane domain VII, which binds to the retinal chromophore to form a photopigment. ; Some xenopsins possess a tripeptide motif, NxQ, which is also found in ciliary opsins and known to be crucial for G-protein activation. A number of flatworm xenopsin sequences in clade A have similar NxQ patterns (including Maritigrella - NAQ), while the motif differs considerably in the polyclad xenopsins of clade B, cnidopsins, bathyopsins and tetraopsins. An alignment of the C-terminal regions of ciliary opsins, xenopsins, cnidopsins, tetraopsins and bathyopsins shows, at a conserved position, similar VxPx motifs in flatworm clade A xenopsins (including Mc xenopsin - VSPQ) as well as a mollusk (A. irradiens) and brachiopod (T. transversa) xenopsin, it is also present in ciliary opsins from non-vertebrate chordates (tunicate and lamprey) and annelids, as well as in cnidopsin sequences. This motif binds the small GTPase Arf4 to direct vertebrate rhodopsin (a ciliary opsin) to the primary cilia. The presence of this motif in some ciliary opsins, xenopsins, cnidopsins may suggest a shared mechanism for the active delivery of these opsins to the cilia in CPRs.

Figure 1—figure supplement 3. Alignment of major opsin clades showing conserved lysine in transmembrane domain VII, which binds to the retinal chromophore to form a photopigment. ; Some xenopsins possess a tripeptide motif, NxQ, which is also found in ciliary opsins and known to be crucial for G-protein activation. A number of flatworm xenopsin sequences in clade A have similar NxQ patterns (including Maritigrella - NAQ), while the motif differs considerably in the polyclad xenopsins of clade B, cnidopsins, bathyopsins and tetraopsins. An alignment of the C-terminal regions of ciliary opsins, xenopsins, cnidopsins, tetraopsins and bathyopsins shows, at a conserved position, similar VxPx motifs in flatworm clade A xenopsins (including Mc xenopsin - VSPQ) as well as a mollusk (A. irradiens) and brachiopod (T. transversa) xenopsin, it is also present in ciliary opsins from non-vertebrate chordates (tunicate and lamprey) and annelids, as well as in cnidopsin sequences. This motif binds the small GTPase Arf4 to direct vertebrate rhodopsin (a ciliary opsin) to the primary cilia. The presence of this motif in some ciliary opsins, xenopsins, cnidopsins may suggest a shared mechanism for the active delivery of these opsins to the cilia in CPRs.