Odorant coreceptor which complexes with conventional odorant receptors (ORs) to form odorant-sensing units, providing sensitive and prolonged odorant signaling and calcium permeability. Orco is a universal and integral part of the functional odorant receptor, involved in the dendritic localization of other olfactory receptors. Can form functional ion channels in the absence of an odor-binding OR. Plays a key role in preferred attraction of females for humans over non-human hosts for blood feeding. Human attraction plays a crucial role in the transmission of Plasmodium protozoans by the mosquito leading to infection diseases like malaria. Also required for the response to N,N-Diethyl-meta-toluamide (DEET), the most widely used insect repellent worldwide. Heterodimer with conventional odorant receptors (ORs). Complexes exist early in the endomembrane system in olfactory sensory neurons (OSNs), coupling these complexes to the conserved ciliary trafficking pathway. Expressed in olfactory and gustatory organs of both adult and immature stages. Highest expression is seen in adult antennae and the maxillary palps. Lower expression also seen in proboscis and legs. Within the antenna, expression originates in cell bodies and projects into the lumen of an individual sensillum, presumably along the dendritic extension of the neuron. Within the maxillary palps, expression is seen in a small number of cell bodies and in projections into the sensillar cone. Within the probiscus, expression is seen in a single type of sensillum on the outer surface of the labellar lobes. Expressed in preimago stages, including early stage larvae, late-stage larvae, and pupae, but not in embryos. The atypical heteromeric and topological design of the odorant receptors appears to be an insect-specific solution for odor recognition, making the OR/Orco complex an attractive target for the development of highly selective insect repellents to disrupt olfactory-mediated host-seeking behaviors of insect disease vectors. Odor-evoked OR currents are independent of known G-protein-coupled second messenger pathways. The homomeric Orco channel is thought to be a cyclic-nucleotide-gated ion channel that depolarizes the olfactory receptor neuron. While many natural and synthetic odorants have been shown to agonize Orco/Or complexes, only a single direct Orco agonist, VUAA1, has been described. On the contrary, amiloride derivatives block Orco/Or complexes. Belongs to the insect chemoreceptor superfamily. Heteromeric odorant receptor channel (TC 1.A.69) family. Orco subfamily. The senses confused - Issue 161 of June 2014