Deciphering the Flupyrimin Binding Surface on the Insect Nicotinic Acetylcholine Receptor.

A novel insecticide flupyrimin (FLP) with a trifluoroacetyl pharmacophore acts as an antagonist at the insect nicotinic acetylcholine receptor (nAChR). This investigation examines a hypothesis that the FLP C(O)CF3 moiety is primarily recognized by the β subunit-face in the ligand-binding pocket (interface between α and β subunits) of the insect nAChR. Accordingly, we evaluate the atomic interaction between a fluorine atom of FLP and the partnering amino acid side chain on the β subunit employing a recombinant hybrid nAChR consisting of aphid Mpα2 and rat Rβ2 subunits (with a mutation at T77 on the Rβ2). The H-donating T77R, T77K, T77N, or T77Q nAChR enhances the FLP binding potency relative to that of the wild-type receptor, whereas the affinity of neonicotinoid imidaclprid (IMI) with a nitroguanidine pharmacophore remains unchanged. These results facilitate the establishment of the unique FLP molecular recognition at the Mpα2/Mpβ1 interface structural model, thereby underscoring a distinction in its binding mechanism from IMI.