Antagonist profile and molecular dynamic simulation of a Drosophila melanogaster muscarinic acetylcholine receptor

A stably-transfected, Drosophila cell line (S2-DM1-1) expressing the Drosophila DM1 muscarinic acetylcholine receptor (mAChR) exhibits high affinity, saturable, specific binding of the radiolabelled muscarinic antagonist [3H]-N-methyl scopolamine ([3H]-NMS) with an equilibrium dissociation constant (K(d)) of 0.67 ± 0.02 and a B(max) of 1.53 ± 0.3 pmol/mg protein. Displacement of [3H]-NMS by mAChR antagonists results in the pharmacological profile: 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) > hexahydrosiladifenidol > p-fluorohexahydrosiladifenidol > nitrocaramiphen > pirenzepine > methoctramine > AFDX-116. This antagonist profile most closely resembles that of the vertebrate M3 mAChR subtype. In this study, however, we have demonstrated that the antagonist profile of DM1 is distinct from those of vertebrate mAChR subtypes. Molecular dynamic simulations of the Drosophila muscarinic receptor are presented in the free, carbamylcholine-bound and NMS-bound forms. Theoretical, quantitative structure-activity relationship models have been developed; a good correlation is observed between the interaction energies of the minimized ligand-receptor complexes and the pharmacological affinities of the antagonists tested.