1.A.69.3.1
Fructose-regulated Ca²⁺/cation channel, Gustatory (fructose) receptor-9, Gr9 (Sato et al., 2011). Gr9 is widely expressed in the central nervous system (CNS), as well as oral sensory organs and is involved in the promotion of feeding behaviors (Mang et al. 2016). GRs play roles in sensing tastants, such as sugars and bitter substances. The BmGr9 silkworm GR is a d-fructose-gated ion channel receptor. Morinaga et al. 2022 presented a structural model for a channel pore and a D-fructose binding site in BmGr9. Since the membrane topology and oligomeric state of BmGr9 appears similar to those of an insect odorant receptor co-receptor, Orco, they constructed a structural model of BmGr9 based on the cryo-EM Orco structure. Their site-directed mutagenesis data suggested that transmembrane region 7 forms channel pore and controls channel gating. This model also suggested that a pocket formed by transmembrane helices 2-4 and 6 binds D-fructose. They determined the potent binding mode of D-fructose. They proposed a conformational change that leads to channel opening upon D-fructose binding (Morinaga et al. 2022).