Identification of mosquito olfactory receptors capable of detecting nitro compounds

Insects possess an advanced olfactory system capable of detecting a wide range of odors through seven-transmembrane olfactory receptors (ORs). These ORs form heteromeric complexes with olfactory receptor co-receptor, Orco, and upon binding to specific ligands, they trigger the intracellular influx of ions such as sodium and calcium. Identifying ORs that respond to chemical molecules released from explosives holds significant importance for the development of biosensors for security and humanitarian purposes. In this study, screening of 196 mosquito ORs in HEK293FT cells for intracellular calcium flux on nitro compound administrations identified ORs as sensors for 2,4-dinitrotoluene, 2-nitroaniline, 2,3-dinitrotoluene, 2,6-dinitrotoluene, and 4-amino-2,6-dinitrotoluene. The different odor response profiles exhibited by naturally occurring polymorphisms or indels in the single OR gene that we had cloned were also explored. Sequence comparisons on these natural genetic variations and heterologous expression of each variant resulted in the identification of the amino acid positions involved critically in the gain and loss of odor sensitivity. Furthermore, we found that various combinations of the identified positions and different amino acid residues artificially evolve the OR with a higher sensitivity to nitro compounds. Our findings pave the way for the development of high-performance explosive detection biosensors, significantly contributing to technological advancements in landmine clearance and other areas. Additionally, our established screening system suggests the potential for identifying insect ORs that could serve as elements for various biosensors beyond explosive detection.