Insect-vertebrate chimeric nicotinic acetylcholine receptors identify a region, loop B to the N-terminus of the Drosophila Dα2 subunit, which contributes to neonicotinoid sensitivity

A chimera based on the chicken α4 nicotinic acetylcholine receptor (nAChR) subunit containing an insert from loop B to the N-terminus of the Drosophila melanogaster Dα2 (=SAD) subunit was constructed and co-expressed with the chicken β2 nAChR subunit in Xenopus laevis oocytes. The actions of the neonicotinoid insecticide imidacloprid were examined. Replacement of the region loop B to the N-terminus of the α4 subunit by the corresponding region of the Dα2 subunit had little effect on the concentration-response curve for imidacloprid. However, replacement of Glu219 by proline in the YXCC motif in loop C of the chimeric α4 subunit resulted in a marked displacement to the left of the concentration-response curve for imidacloprid not seen when an equivalent mutation was made in the α4β2 nAChR. The results suggest that the region loop B to the N-terminus in the Dα2 subunit contributes to the high imidacloprid sensitivity of the hybrid Dα2β2 nAChR.