Identification of the locust proctolin receptor and design of proctolin analogs

Proctolin (Arg-Tyr-Leu-Pro-Thr) is a neuropeptide found in insects and crustaceans, known for its diverse physiological roles, including potent myotropic activity in both visceral and skeletal muscles. Proctolin receptor was first identified in Drosophila based on its response to proctolin stimulation. Through sequence similarity analysis, putative proctolin receptors have been identified in other insect species, although their functions have not been validated.

In this study, we identified LmProcR (a proctolin receptor of locust Locusta migratoria) experimentally. We found that upon proctolin stimulation, LmProcR mediated an increase in intracellular calcium ion (Ca²⁺) levels and the translocation of β-arrestin-2 from the cytoplasm to the plasma membrane. Using AlphaFold3, we predicted the structure of the LmProcR-proctolin complex, revealing that LmProcR is a G-protein-coupled receptor with a canonical seven-transmembrane topology. Proctolin binds to a deep pocket formed by the transmembrane helices, with an intriguing feature being a cavity beneath the amino nitrogen of Arg1 in proctolin. This structural insight suggests that novel proctolin analogs could be developed through N-terminal modifications. Guided by the predicted structure of the LmProcR-proctolin complex, we designed five N-terminally modified proctolin analogs and discovered that attaching a d-alanine to the N-terminus of proctolin significantly enhances its myotropic activity in inducing locust foregut contractions.

The identification of LmProcR and the structural prediction of the LmProcR-proctolin complex provide a foundation for designing novel proctolin mimics and developing proctolin-based insecticides. © 2025 Society of Chemical Industry.