A constitutively active G protein-coupled acetylcholine receptor regulates motility of larval Schistosoma mansoni

Abstract

The neuromuscular system of helminths controls a variety of essential biological processes and therefore represents a good source of novel drug targets. The neuroactive substance, acetylcholine controls movement of Schistosoma mansoni but the mode of action is poorly understood. Here, we present first evidence of a functional G protein-coupled acetylcholine receptor in S. mansoni, which we have named SmGAR. A bioinformatics analysis indicated that SmGAR belongs to a clade of invertebrate GAR-like receptors and is related to vertebrate muscarinic acetylcholine receptors. Functional expression studies in yeast showed that SmGAR is constitutively active but can be further activated by acetylcholine and, to a lesser extent, the cholinergic agonist, carbachol. Anti-cholinergic drugs, atropine and promethazine, were found to have inverse agonist activity towards SmGAR, causing a significant decrease in the receptor’s basal activity. An RNAi phenotypic assay revealed that suppression of SmGAR activity in early-stage larval schistosomulae leads to a drastic reduction in larval motility. In sum, our results provide the first molecular evidence that cholinergic GAR -like receptors are present in schistosomes and are required for proper motor control in the larvae. The results further identify SmGAR as a possible candidate for antiparasitic drug targeting.

Profiling G protein-coupled receptors of Fasciola hepatica identifies orphan rhodopsins unique to phylum Platyhelminthes

“…Numbering relative to PaOAR, except for Y412 which is shown relative to BmOAR. (D) Acetylcholine receptor ligand binding residues as characterised by homology modelling of the S. mansoni G protein-coupled acetylcholine receptor (SmGAR) [62]; numbering relative to SmGAR. In each case, only F. hepatica sequences displaying at least 75% identity across the stated ligand binding residues are shown.…”

“…Two putative muscarinic acetylcholine receptors (mAChRs), shared highest LBD identity with a Rat M3 ACh receptor (Figure 4D) [61]. Although these were only 67% identical to the rat sequence, the five ligand-interacting residues within their LBDs were 100% identical to those of a deorphanised S. mansoni mAChR, known to be involved in neuromuscular coordination (SmGAR) [62]. These receptors (D915_00814 and BN1106_s1913B000092) were also the most similar to SmGAR in our phylogeny (S5 Figure) so we consider them amongst our high confidence candidates for deorphanization.…”

Kinetic profiling an abundantly expressed planarian serotonergic GPCR identifies bromocriptine as a perdurant antagonist

“…1) and is amenable to miniaturization to facilitate higher throughput drug screening campaigns against flatworm GPCRs (Chan et al., 2016b). Obviously, this approach method is useful only for GPCRs that modulate cellular cAMP levels (G s , G i ), but this reflects a coupling specificity of the majority of flatworm GPCRs examined in heterologous systems to date (Omar et al., 2007, Taman and Ribeiro, 2009, Zamanian et al., 2012, Patocka et al., 2014, MacDonald et al., 2015). Probes for other second messenger pathways (for example genetically encoded Ca 2+ indicators) are available and have also been shown to be useful for deorphanizing lophotrochozoan GPCR activity (Bauknecht and Jekely, 2015).…”

Pharmacological profiling an abundantly expressed schistosome serotonergic GPCR identifies nuciferine as a potent antagonist

“…In this context, several recent studies have begun to establish the role(s) of individual GPCRs within the excitable cell niche (El-Shehabi et al., 2012, Patocka et al., 2014, Chan et al., 2015, MacDonald et al., 2015). Of relevance to this study, is the identification of a serotonergic GPCR (Sm.5HTR L ) that has been shown by RNAi approaches to control larval and adult worm motility (Patocka et al., 2014).…”