Drosophila odorant receptors are both ligand-gated and cyclic-nucleotide-activated cation channels

Insect odorant receptors In many organisms, from worms to humans, olfactory cues are detected by large families of seven transmembrane-spanning receptors, which have until now been classified as G protein-coupled receptors. Insects, however, have evolved a surprisingly simple and efficient sense of smell in which the odorant receptors require a second component — the ion-channel-forming chaperone protein Or83b — for correct function. In the first of two related papers, Sato et al. show that these heteromeric receptors form ligand-gated cation channels that are not dependent on G protein-coupled second messengers, and speculate that other seven transmembrane-spanning proteins may show similar ion channel activity. Wicher et al. show that, in addition to direct channel activation, ligand binding to odorant receptors causes G protein-coupled channel activation. This work has implications for the search for insect odorant receptor inhibitors for possible use in controlling host seeking behaviour of disease carrying insects such as the mosquito.