Agonism of mosquito and human transient receptor potential ankyrin 1 (TRPA1) channels by the natural drimane sesquiterpene cinnamodial

TRPA1 channels are multi-modal receptors in animals for sensing noxious physical and chemical factors. They are considered promising biochemical targets for developing repellents of arthropod disease vectors and drugs to treat a variety of medical conditions including pain, inflammation, and itch. Recently, we discovered that cinnamodial (CDIAL), a natural drimane sesquiterpene produced by the medicinal plant Cinnamosma fragrans, agonizes mosquito TRPA1 channels and is antifeedant and repellent to Aedes aegypti. However, the selectivity of CDIAL for mosquito vs. human TRPA1 and how CDIAL binds to TRPA1 channels are unknown. Here we characterize the agonism by CDIAL of Aedes aegypti (Aa) and Homo sapiens (Hs) TRPA1 channels and compare it to that induced by two other known TRPA1 agonists, nepetalactone and JT010. Heterologous expression of AaTRPA1 and HsTRPA1 in Xenopus laevis oocytes revealed that CDIAL agonized both channels with similar potency. Nepetalactone was less potent of an agonist than CDIAL for both AaTRPA1 and HsTRPA1, but was a more specific agonist for AaTRPA1 over HsTRPA1 compared to CDIAL. JT010 did not detectably activate AaTRPA1, but was a more potent agonist of HsTRPA1 than CDIAL. To generate insights into a putative binding site of CDIAL on AaTRPA1 we mutated six Lys residues (656, 678, 681, 728, 738, 744) and/or a Cys residue (684) in the coupling domain previously hypothesized to be involved. Simultaneous mutation of the six Lys residues to Ala dampened agonistic responses of AaTRPA1 to CDIAL, whereas changing Cys684 to Ser had no detectable impact. Protein modeling and molecular docking simulations for both AaTRPA1 and HsTRPA1 suggest species-specific CDIAL-binding mechanisms to the coupling domain, which involve Lys681 in AaTRPA1 and Cys621 in HsTRPA1.