A divergent member of the transforming growth factor β receptor family from Schistosoma mansoni is expressed on the parasite surface membrane

To optimize reproductive success under the limitations determined by conditions within an individual host, parasitic helminths have evolved mechanisms that allow them to detect and respond to host factors such as species, age, sex, reproductive condition, and immune status. Using the model helminth Schistosoma mansoni, we have explored the possibility that parasitic helminths express signal-transducing receptor molecules on their surfaces. Here, we present the identification of a schistosome member of the transforming growth factor ̄ receptor family of cell-surface receptors, the first member of this family to be identified in a platyhelminth. The putative protein kinase domain of the schistosome receptor displays up to 58% amino acid identity to kinase domains of other type I receptor serine-threonine kinases, and contains a potential 'GS domain,' suggesting it is a divergent member of the type I receptor subfamily. This receptor is expressed on the surface of the parasite's syncytial tegument and expression of receptor messenger RNA and protein is up-regulated following infection of the mammalian host. The receptor protein can be isolated in a phosphorylated form from adult parasites, which together with its surface location, suggests that it functions in transducing signals across the parasite surface membrane.