A DIVERGENT MEMBER OF THE TRANSFORMING-GROWTH-FACTOR-BETA RECEPTOR FAMILY FROM SCHISTOSOMA-MANSONI IS EXPRESSED ON THE PARASITE SURFACE-MEMBRANE

To optimize reproductive success under the limitations determined by c onditions 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 possibil ity that parasitic helminths express signal-transducing receptor molec ules on their surfaces. Here, we present the identification of a schis tosome member of the transforming growth factor beta receptor family o f cell-surface receptors, the first member of this family to be identi fied in a platyhelminth, The putative protein kinase domain of the sch istosome receptor displays up to 58% amino acid identity to kinase dom ains of other type I receptor serine-threonine kinases, and contains a potential ''GS domain,'' suggesting it is a divergent member of the t ype I receptor subfamily. This receptor is expressed on the surface of the parasite's syncytial tegument and expression of receptor messenge r RNA and protein is up-regulated following infection of the mammalian host. The receptor protein can be isolated in a phosphorylated form f rom adult parasites, which together with its surface location, suggest s that it functions in transducing signals across the parasite surface membrane.