The Apis mellifera alpha 5 nicotinic acetylcholine receptor subunit expresses as a homomeric receptor that is sensitive to serotonin

Insect nicotinic acetylcholine receptors (nAChRs) are molecular targets of highly effective insecticides such as neonicotinoids. Functional expression of these receptors provides useful insights into their functional and pharmacological properties. Here, we report that the alpha 5 nAChR subunit of the honey bee, Apis mellifera, functionally expresses in Xenopus laevis oocytes, which is the first time a homomeric insect nAChR has been robustly expressed in a heterologous system without the need for chaperone proteins. Using two-electrode voltage-clamp electrophysiology we show that the alpha 5 receptor has low sensitivity to acetylcholine with an EC50 of 2.37 mM. However, serotonin acts as an agonist with a considerably lower EC50 at 119 mu M that is also more efficacious than acetylcholine in activating the receptor. Molecular modelling indicates that residues in the complementary binding site may be involved in the selectivity towards serotonin. This is the first report of a ligand-gated ion channel activated by serotonin from an insect and phylogenetic analysis shows that the alpha 5 subunit of A. mellifera and other non-Dipteran insects, including pest species, belong to a distinct subgroup of subunits, which may represent targets for the development of novel classes of insecticides.

Automated summary

This study presents the functional expression of the alpha 5 nAChR subunit from honey bees in a heterologous system, revealing its low sensitivity to acetylcholine and the efficacy of serotonin as an agonist. Molecular modelling suggests that residues in the binding site may play a role in the receptor's selectivity towards serotonin. This finding may provide potential targets for the development of novel insecticides.