Isolation and partial characterization of three members of the GGR-1 family in the parasitic nematode Haemonchus contortus

Abstract

Haemonchus contortus is a blood sucking parasitic nematode that infects ruminant animals. These parasites are of significant economic importance as they are estimated to cost the agricultural industry billions of dollars each year in management. Reliance and overuse of drugs has resulted in resistance, and there is an urgent need for novel anti-parasitic drugs. Cys-loop ligand gated ion channels have been recognized as important invertebrate specific drug targets. However, specific targets must be identified and characterized prior to drug development. This thesis describes the identification and partial characterization of three ion channel subunits from the GGR-1 family – Hco-lgc-39, Hco-lgc-40, and Hco-ggr-2. The phylogenetic analysis conducted in this study revealed that these genes are widely conserved across several different parasitic nematodes. Two of these genes, lgc-39 and ggr-2, have not been previously characterized in another organism. Although lgc-40 has been previously investigated in C. elegans, the channel found in H. contortus was found to be similarly sensitive to choline and 18-fold more sensitive to acetylcholine. This increased sensitivity to acetylcholine could potentially indicate a different function in H. contortus. Pharmaceutical characterization of Hco-LGC-39, revealed that this protein subunit forms a homomeric channel that is responsive to acetylcholine, and to a higher degree, methacholine. A ligand for the Hco-GGR-2 homomeric channel has not yet been identified. Additionally, homology modelling of Hco-LGC-39 and Hco-LGC-40 provided further insight into receptor ligand interactions, and helped to identify several residues that may be important for ligand binding. This partial characterization of unique receptor subunits provides the beginning step for the production of novel anthelminthic drugs to combat the increasingly problematic parasite, H. contortus.