Molecular modelling of the adipokinetic hormone receptor from the stick insect Carausius morosus, and its endogenous agonist

This study combines NMR spectroscopy, molecular dynamics (MD), and docking simulations to elucidate the structure, dynamics, and receptor interactions of the decapeptide Carmo-HrTH-II, from the stick insect, Carausius morosus . NMR analysis revealed a flexible peptide adopting a β-turn between Pro⁶ and Asn⁷, a feature retained during MD simulations and critical for receptor recognition. Docking Carmo-HrTH-II to the Carmo-AKHR homology model identified a stable binding mode in which Phe⁴ and Trp⁸ lie within the binding pocket, consistent with their known importance for GPCR activation. Alanine-scanning mutagenesis and residue scanning demonstrated strong agreement between calculated binding energies and experimental EC₅₀ values, confirming the essential roles of Phe⁴, Pro⁶, Asn⁷, and Trp⁸ in receptor activation. Comparative studies of Carmo-HrTH-I and other AKH analogues showed that position 10 substitutions have minimal influence on binding, whereas position 3 substitutions significantly alter affinity. In silico screening of insecticide-like compounds identified several potential receptor antagonists that bind to the same site as Carmo-HrTH-II. These ligands interact predominantly through π–π stacking and hydrogen bonding, disrupting the conserved salt bridge essential for receptor activation. Together, these results provide a molecular basis for AKH receptor activation and suggest a new route for the rational design of AKH-targeted insecticides.