Calmodulin Modulation of Insect Ryanodine Receptor

Abstract Ryanodine receptor (RyR) is a giant calcium release channel located on the membrane of the endoplasmic reticulum (ER). As a key protein in the calcium signaling pathway, RyR function is modulated by a number of protein and small molecule modulators. Although RyR has been identified as an important insecticide target, the regulation of insect RyR by some of these modulators is still largely unknown. 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 a mammalian RyR sequence. Interestingly, the enhanced binding of CaM in the mutant insect RyR resulted in increased sensitivity to the diamide insecticide chlorantraniliprole (CHL), suggesting that this CaM-CaMBD interface could be targeted by potential synergists. The thermodynamics of the binding between insect CaM and CaMBD was characterized by ITC and the key residues responsible for the insect-specific regulation were identified through mutagenesis studies. Finally, a homology model was created to predict the CaM-binding mode in insect RyR, which can be used to guide the structure-based design of future pesticides.