Structural Insights into the Diamide Modulation of Ryanodine Receptor

Abstract

Diamide insecticides, developed by pesticide giants DuPont, Bayer and Syngenta, are among the top-selling insecticides globally, with annual sales >USD$2 billion. They are used to control a wide range of pests by targeting their ryanodine receptors (RyRs). However, due to heavy usage, many pests have developed strong resistance, posing a threat on food safety in many countries. Here, we report the highest-resolution cryo-electron microscopy (cryo-EM) structure of RyR1 in the open state, in complex with the anthranilic diamide chlorantraniliprole (CHL). The 3.2 Å local resolution map allows for the unambiguous assignment of the CHL binding site, which is located in the pseudo-voltage-sensor domain of RyR. The molecule induces a conformational change by affecting the S4-S5 linker, triggering channel opening. The binding site is further corroborated with data from cellular and drosophila mutagenesis studies, which reveal how diamide insecticides are selective to the Lepidoptera group of insects over honeybee or mammal RyRs. Importantly, our data reveals that several pests have developed resistance via two mechanisms, either by mutating key residues involved in binding or by introducing steric hindrance. Mutations in human RyRs are associated with inherited myopathies. Based on the activities of diamides against the mutant mammalian RyRs, we propose to develop therapeutic molecules targeting the allosteric diamide-binding site with the aim to treat human myopathies. Our findings provide a foundation for developing novel pesticides to overcome the resistance crisis, and to decrease toxicity for humans and beneficial insects. It also highlights an allosteric site that can be targeted for novel therapeutics in humans.