Fig. 6

The chemosensory ionotropic receptor IR25a is conserved in marine sedentarians (spionids and siboglinids). A Alignment of the S1 and S2 ligand-binding domains from seven candidate IR25a proteins. Three key ligand-binding residues (R, T, and D/E) are marked with an asterisk; S1 and S2 domains by horizontal orange lines. B Schematic representation of IR25a protein is shown. C AlphaFold2 prediction of L. polybranchiata IR25a. The structure shows distinct domains, including the amino-terminal domain (ATD), the ligand-binding domain (LBD), and the transmembrane domain (TMD). D Alignment of LBD structure of IR25a of L. polybranchiata (red) and Drosophila melanogaster (turquoise). Accession number: phauc_IR25a (XP_059149035), drmel_IR25a (NP_001260049)