ShAR2β, a divergent nicotinic acetylcholine receptor subunit from the blood fluke Schistosoma

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate the fast actions of the neurotransmitter, acetylcholine. Invertebrate nAChRs are of interest as they are targets of widely-selling insecticides and drugs that control nematode parasites. Here, we report the cloning of ShAR2 beta, a candidate nAChR subunit from the blood fluke, Schistosoma haematobium, which is the third trematode nAChR subunit to be characterized. While ShAR2 beta possesses key structural features common to all nAChRs, its amino acid sequence shares considerably low identity with those of insect, nematode and vertebrate nAChR subunits. In particular, the second transmembrane domain of ShAR2 beta, which lines the ion channel, bears unusual amino acid residues which will likely give rise to a receptor with distinct functional properties. Phylogenetic analysis shows that ShAR2 beta is a divergent nAChR subunit that may define a clade of trematode-specific subunits. We discuss our findings in the context of potentially exploiting this receptor as a target for controlling schistosome parasites.