Molecular characterization and imidacloprid selectivity of nicotinic acetylcholine receptor subunits from the peach-potato aphid Myzus persicae

The recent introduction of the chloronicotinyl insecticide imidacloprid, targeting insect nicotinic acetylcholine receptors (nAChRs), emphasises the importance of a detailed molecular characterisation of these receptors. We are investigating the molecular diversity of insect nAChR subunit genes in an important agricultural pest, the peach-potato aphid Myzus persicae, Two M, persicae alpha-subunit cDNAs, Mp alpha 1 and Mp alpha 2, have been cloned previously. Here we report the isolation of three novel alpha-subunit genes (Mp alpha 3-5) with overall amino acid sequence identities between 43 and 76% to characterised insect nAChR subunits, Alignment of their amino acid sequences with other invertebrate and vertebrate nAChR subunits suggests that the insect alpha subunits evolved in parallel to the vertebrate neuronal nAChRs and that the insect non-alpha subunits are clearly different from vertebrate neuronal beta and muscle non-alpha subunits, The discovery of novel subtypes in M. persicae is a further indicator of the complexity of the insect nAChR gene family. Heterologous co-expression of M. persicae nAChR alpha-subunit cDNAs with the rat beta 2 in Drosophila S2 cells resulted in high-affinity binding of nicotinic radioligands. The affinity of recombinant nAChRs for [H-3]imidacloprid was influenced strongly by the alpha subtype, This is the first demonstration that imidacloprid selectively acts on Mp alpha 2 and Mp alpha 3 subunits, but not Mp alpha 1, in M, persicae.