Calmodulin Modulation of Insect Ryanodine Receptors

Ryanodine receptor (RyR) is a giant calcium release channel located on the membrane of the endoplasmic reticulum (ER). Here, we report the regulation of RyRs from two major agricultural pests, diamondback moth and fall armyworm, by insect calmodulin (CaM). The recombinantly expressed full-length insect RyR could be pulled down by insect CaM in the presence of Ca2+, but the efficiency is lower compared to rabbit RyR1 and insect RyR with the CaM-binding domain (CaMBD) replaced by rabbit RyR1 sequence. Interestingly, the enhanced binding of CaM in the mutant insect RyR resulted in an increased sensitivity to the diamide insecticide chlorantraniliprole (CHL), suggesting that this CaM-CaMBD interface could be targeted by potential synergists acting as molecular glue. The thermodynamics of the binding between insect CaM and CaMBD was characterized by isothermal titration calorimetry, and the key residues responsible for the insect-specific regulation were identified through mutagenesis studies.