1.A.69.2.6
Gustatory receptor-like (Grl or Gr5a) protein of 444 aas and 8 TMSs. Insect odorant receptors and gustatory receptors define a superfamily of seven- or 8-TMS ligand-gated ion channels (referred to here as 7TMICs), with homologs identified across Animalia, except Chordata, as well as in plants and uncellular eukaryotes (DUF3537 proteins). Several Drosophila melanogaster Grls display selective expression in subsets of taste neurons, suggesting that they are previously- unrecognized insect chemoreceptors. Their origin may be in a eukaryotic common ancestor (Benton and Himmel 2023). It is required for a response to the sugar trehalose in taste neurons (Ueno et al. 2001). Gr5a neurons selectively respond to sugars, in contrast to Gr66a cells which respond to bitter compounds. Flies are attracted to sugars and avoid bitter substances, suggesting that Gr5a neuron activity is sufficient to mediate acceptance behavior. Sugar signal transduction occurs through coupling with G-proteins such as Galpha49B and G-salpha60A.