Insect olfactory receptors (also known as odorant receptors, ORs) are expressed in the cell membranes of the olfactory sensory neurons of insects. Similarly to mammalian olfactory receptors, in insects each olfactory sensory neuron expresses one type of OR, allowing the specific detection of a volatile chemical.
In contrast to vertebrate ORs, which are seven transmembrane G protein coupled receptors (GPCRs), insect ORs are part of an unrelated group of ligand-gated ion channels. Like GPCRs, insect ORs are transmembrane proteins with seven transmembrane helices, but with a reversed topology, with an intracellular N-terminus and an extracellular C-terminus. Differently to mammalian ORs, insect ORs form a heteromer with a fixed monomer, Orco, and a variable OR monomer, which confers the odour specificity.
