The cattle tick is Australia’s most serious external parasite of cattle and presents significant problems for the cattle industry. Current insecticides used against cattle ticks are nonselective, which presents issues for beneficial insects such as dung beetles.
Ecdysone receptor proteins regulate many major developmental processes in insects and vary subtly in three-dimensional structure between insect taxa. This variation provides an opportunity for the discovery and design of molecules that selectively bind to and interfere with pest ecdysone receptor proteins. We aim to discover lead compounds against the ecdysone receptor proteins that can be developed into commercial pesticides that are selectively toxic to cattle ticks but safe for dung beetles, humans, and other organisms in the environment.
The ecdysone receptor proteins are generally a heterodimer of the ecdysone receptor (EcR) subunit and the ultraspiracle (USP) subunit. We have cloned and expressed EcR with a histidine-tag and USP with a streptavidin-tag for cattle tick and dung beetle. To purify the proteins, we used affinity purification followed by size-exclusion chromatography. Protein quality was validated through intact mass spectrometry analysis, confirming molecular mass and purity, while functional integrity was demonstrated using fluorescence polarization assays to verify ligand-binding ability. With these purified proteins in hand, we will next conduct chemical library screens to search for molecules that could selectively bind the cattle tick EcR while having lower affinity for the dung beetle homologue.