1.A.69.3.2
Gustatory receptor 43a isoform A.  Functions as a narrowly tuned fructose receptor in taste neurons (Miyamoto et al. 2012), being both necessary and sufficient to sense hemolymph fructose.  The structures of two sugar GRs have been determined (Ma et al. 2024), the Drosophila sweet taste receptors GR43a and GR64a in the apo and sugar-bound states. Both GRs form tetrameric sugar-gated cation channels composed of one central pore domain (PD) and four peripheral ligand-binding domains (LBDs). Whereas GR43a is specifically activated by the monosaccharide fructose that binds to a narrow pocket in LBDs, disaccharides sucrose and maltose selectively activate GR64a by binding to a larger and flatter pocket in LBDs. Sugar binding to LBDs induces local conformational changes, which are subsequently transferred to the PD to cause channel opening (Ma et al. 2024).