Schistosoma mansoni: characterization of p50, an immunophilin

A 1.4-kb cDNA clone encoding a 50-kDa homologue of p59, a heat shock binding immunophilin, has been isolated from a Schistosoma mansoni cercariae cDNA library. We have designated this clone S. mansoni p50 (Smp50). From the sequence comparison, we speculate that Smp50 is similar in structural organization to other p59 proteins. As with other p59s, Smp50 also shows homology to various FK binding proteins (FKBPs). The amino acids in human FKBP12 which are proposed to be important for FK506 interaction are conserved in the schistosome protein. We have expressed and purified the recombinant protein (rSmp50) from Escherichia coli. rSmp50 demonstrated peptidyl-prolyl cis-transisomerase (PPIase) activity, typical of immunophilins. Western blot analysis of extracts from S. mansoni adult worms probed with rabbit polyclonal antisera, generated against the recombinant polypeptide, has indicated the presence of Smp50 in the parasite. The antisera did not cross-react with proteins from E. coli or HeLa cell extracts. All of the p59s characterized to date have been from vertebrate species. Therefore, our finding represents the first identification of the protein in an invertebrate system.