ANTAGONIST PROFILE AND MOLECULAR DYNAMIC SIMULATION OF A DROSOPHILA-MELANOGASTER MUSCARINIC ACETYLCHOLINE-RECEPTOR

A stably-transfected, Drosophila cell line (S2-DM1-1) expressing the D rosophila DM1 muscarinic acetylcholine receptor (mAChR) exhibits high- affinity, saturable, specific binding of the radiolabelled muscarinic antagonist [H-3]-N-methyl scopolamine ([H-3]-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 [H-3]-NMS by mAChR antagonists res ults in the pharmacological profile: 4-diphenylacetoxy-N-methylpiperid ine methiodide (4-DAMP) > hexahydrosiladifenidol > p-fluorohexahydrosi ladifenidol > nitrocaramiphen > pirenzepine > methoctramine > AFDX-116 . This antagonist profile most closely resembles that of the vertebrat e M3 mAChR subtype. In this study, however, we have demonstrated that the antagonist profile of DM1 is distinct from those of vertebrate mAC hR subtypes, Molecular dynamic simulations of the Drosophila muscarini c receptor are presented in the free, carbamylcholine-bound and NMS-bo und forms. Theoretical, quantitative structure-activity relationship m odels have been developed; a good correlation is observed between the interaction energies of the minimized ligand-receptor complexes and th e pharmacological affinities of the antagonists tested.