α7 mutants mimicking atypical motifs (YxxCC of loop-C, and E to H at −1′ in TM2) in the C. elegans LEV-8 subunit affect nicotinic acetylcholine receptor function

Abstract

The ACR-8-like group of C. elegans nicotinic acetylcholine receptor (nAChR) subunits contain unusual motifs in the ACh binding site and in the -1' position of transmembrane region two (TM2). Using site-directed mutagenesis (SDM) we have introduced these motifs into chicken alpha7 as it has not been possible to express C. elegans nAChR in vitro. Oocytes expressing alpha7 with the C. elegans binding motif show a reduced affinity and efficacy for both ACh and nicotine. The blocking action of the anthelmintic drug levamisole is reduced. The TM2 motif resulted in a non-functional receptor. We conclude that the TM2 motif profoundly restricts cation movement through the alpha7 channel but does not confer anion permeability. The altered form of the ACh binding motif is likely to result in a receptor with altered pharmacology, adding potential functional diversity at synapses in the nervous system and neuromuscular junctions of C. elegans.