Putative G protein–coupled receptors in parasitic nematodes—potential targets for the new anthelmintic class cyclooctadepsipeptides?
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Parasitic nematodes cause major problems in livestock animals. Resistances to the most commonly used drugs are arising. The cyclooctadepsipeptide emodepside belongs to a new class of anthelmintics. A receptor for emodepside, Hc110–R, was previously identified in Haemonchus contortus. We have identified the complete coding sequences of putative orthologues in Cooperia oncophora and Ostertagia ostertagi, tri–chostrongyles in cattle. The putative receptors were named depsiphilins. The deduced amino acid sequence of C. oncophora depsiphilin has a similarity of 91% to the O. ostertagi sequence. The similarity of both the C. oncophora and O. ostertagi depsiphilin to Hc110–R is 89%, based on the amino acid sequence. The depsiphilins share 46% identity with the latrophilin–like protein 1 in Caenorhabditis elegans and 47% identity with a hypothetical protein in Caenorhabditis briggsae. Hc110–R and the latrophilin–like proteins of C. elegans were previously reported to be putative G protein–coupled receptors (GPCRs) and to be related to mammalian latrophilins. A seven transmembrane domain, a GPCR proteolytic site, and other conserved domains characteristic of receptors of the latrophilin group were identified within the depsiphilins. Therefore it seems reasonable to allocate the depsiphilins to the previously described latrophilins and latrophilin–like proteins.