Identification of Modifiers of Odor‐Triggered Mosquito Behaviors Acting through Binding to the ORco Subunit of Odorant Receptor Heteromers

Abstract

Insect olfactory receptors (ORs) are heteromeric ion channels consisting of a common subunit, ORco, and one of many variable subunits, ORx, to which odorants acting as receptor agonists or antagonists, bind in an ORx‐specific manner. In cells expressing only ORco, ORco homomers form functional channels that are activated by specific ORco agonists. We have previously shown that mosquito repellents that block odor‐specific responses of multiple ORs of Anopheles gambiae mosquitoes, act as ORco antagonists capable of suppressing in vitro its activation by the ORco agonists. In parallel studies, we have also shown that the in vitro responses of heteromeric receptors induced by ORx‐specific agonists are enhanced by one to two orders of magnitude in the presence of an ORco‐specific agonist. The latter suggested the induction of conformational rearrangements in ORx‐bound heteromeric receptor complexes caused by the binding of the ORco agonist and resulting in enhanced ion influx into the receptor‐expressing cells.To expand on these findings, we have designed a lepidopteran insect cell‐based ORco expression platform that allows the fast screening of collections of chemical compounds for the presence of mosquito ORco agonists and antagonists in a single screening assay. Because mosquitoes are able to detect the presence of olfaction‐relevant molecules in their natural environments, we screened a small collection of volatile organic compounds (VOCs) of natural, plant, insect and bacterial, origin for the presence of relevant bioactive molecules. The screening effort resulted in the identification of several hits acting as ORco‐specific antagonists but no ligands behaving as ORco‐specific agonists. Examination of the bioactivity of three, randomly selected antagonist hits by in vivo repellence assays against Aedes albopictus mosquitoes, which vector a number of infectious agents, established that two of them displayed significant repellent activity with one of them showing anosmia‐causing activity equal to or slightly better than that of an equivalent dose of DEET. These results provide additional proof for the concept that volatile ORco antagonists may modify olfaction‐based mosquito behaviors in a predicted fashion. They also suggest that the newly developed screening platform may yield additional possibilities for enhanced personal protection against indoor and outdoor transmission of malaria and other mosquito‐borne infectious diseases. Screening of additional VOCs aimed at the identification of new ORco agonists and antagonists is in progress.Support or Funding InformationThis work has been supported by the ENAROMaTIC consortium project (grant No FP7‐222927 of the EC) and was carried out in the facilities of the OPENSCREEN‐GR National (Greece) Research Infrastructure.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Identification of 2,4-Di-tert-butylphenol as a Novel Agonist for Insect Odorant Receptors

“…Orco, an OR coreceptor, is widely expressed in OSNs and has a highly conserved sequence across different insect lineages, making it an essential element for olfactory transduction [ 2 , 11 ]. Orco itself is not activated by odorants but responds to agonists [ 12 ]. Conversely, OrX is an odorant-binding subunit capable of detecting volatile molecules when present in liposomes.…”