BPS2026 - Insecticide control of function and assembly of the heteromeric insect TRP channel Nanchung-Inactive

The ability of insects to hear, sense gravity, and detect their body position is conferred by the mechanosensory chordotonal organs. Localized to these organs and critical for these functions are the heteromeric vanilloid-type transient receptor potential (TRPV) channel comprised of Nanchung (Nan) and Inactive (Iav). Not only is this heteromerization required for activity, but a class of insecticides binds to Nan-Iav to regulate its activity to kill piercing-sucking (hemipteran) insects. How this channel assembles and where these insecticides bind was previously unknown. Here, we reveal the architecture of Nan-Iav, which exhibits two types of subunit interfaces at the cytoplasmic ankyrin repeat domains (ARDs), termed the tight and loose junctions. We reveal the binding site of the insecticide afidopyropen (AP), as well as a natural agonist, nicotinamide, is at the tight junction. We show that binding of AP or nicotinamide modulates the ARD conformation to regulate channel function. Moreover, we observed adventitious binding of calmodulin (CaM) to the C-terminus of Iav, which confers Ca 2+ -dependent regulation of channel function also through binding to the ARDs. Finally, while Iav is incapable of forming intact channels, Nan was observed to assemble into non-conducting pentamers in the presence of AP. Shorter incubations of insecticide with the Nan-expressing cells revealed tetramers, trimers, and dimers, as well. This suggests a possible additional mechanism of action for this insecticide in the form of longer-term sequestration of Nan. These discoveries not only advance the field of TRP channel biology, but also facilitate insecticide development, which is vital as increasing insecticide resistance for many other insecticides threatens our food supply and human health.