Identification of Allosteric Modifiers of Mosquito Odorant Receptor Function and Odor‐Triggered Behaviors

Abstract

Insect odorant receptors (ORs) are heteromeric ion channels each consisting of a common subunit, ORco, and one of multiple variable subunits, ORx, to which odorants acting as specific receptor agonists or antagonists bind. In cells expressing the ORco subunit alone, functional homomeric channels are formed that can be activated by specific ORco agonists. We have previously shown that mosquito repellents that inhibit odor‐specific responses of multiple Anopheles gambiae heteromeric receptors are ORco‐specific antagonists. Additionally, the responses of heteromeric receptors induced by ORx‐agonists were significantly enhanced in the presence of an ORco‐agonist (OA), a finding suggesting that OA binding causes structural rearrangements in the liganded ORx heteromers.We are now reporting on the extension of our studies for discovery of A. gambiae ORco agonists and antagonists using an insect cell‐based ORco expression platform that allows fast screening of compound collections. Screening of a collection of volatile organic compounds (VOCs) of natural origin for relevant bioactive ligands resulted in the identification of several hits acting as ORco antagonists. The functional relevance of the identified hits has been established by in vivo repellence assays against Aedes albopictus mosquitoes, which are capable of vectoring a number of infectious agents. Nine newly identified ORco antagonists displayed significant mosquito repellent activities, with three of them causing mosquito anosmia‐like effects similar to those of equivalent doses of the widely used insect repellent DEET. Moreover, binary mixtures of the most active compounds caused stronger repellence effects relative to the single compounds, a finding suggesting the possible existence of different antagonist binding sites on ORco and functional synergies caused by allosteric interactions within the homomer and the heteromers. These results provide proof of concept that natural ORco antagonists may modify olfaction‐based mosquito behaviors in a predicted fashion. Moreover, the screening platform employed in this study yields enhanced possibilities for personal protection against mosquito‐borne infectious diseases.Support or Funding InformationSupported by OPENSCREEN‐GR “An Open‐Access Research Infrastructure of Chemical Biology and Target‐Based Screening Technologies for Human and Animal Health, Agriculture and the Environment” (MIS 5002691) funded under the Action “Reinforcement of the Research and Innovation Infrastructure” of the Operational Program “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020), and LIFE CONOPS (LIFE12 ENV/GR/000466) funded by the European Commission under the program LIFE + Environment Policy and Governance. We thank Asteria Karadima for the repellence test schematic.