Characterization of the Ras homologue of Schistosoma mansoni

Ras is a member of a super-family of guanine-binding or G-proteins. Ras fun ctions as a molecular switch in the transduction of signals generated by th e activation of a variety of cell surface receptors and relays the signals to downstream effecters. Little is known about signal transduction in schis tosomes. In order for Schistosoma mansoni to survive different immune respo nses triggered by the host as well as to migrate from the site of penetrati on at the skin to the final destination in portal circulation, they must re ceive signals from the host environment and respond to them in a way that a llows their survival. We have isolated the schistosome Ras cDNA by using se quence information of the schistosome Ras homologue submitted to the Genban k database. Analysis of the encoded peptide revealed 81% identity and 92% s imilarity with K-Ras from various species. Ras is a single copy gene as det ermined by quantitative hybridization experiments. The cDNA was cloned into pGEX-4T and the expressed peptide was used to generate specific antibody r eagents. Affinity purified antibodies identified a 23 kDa native protein th at localizes to the subtegument. Ras is not associated with the tegument. R as is expressed in all the developmental stages of the parasite. However, R as is over-expressed in female worms compared to males. Schistosome Ras was also shown to be post-translationally modified by addition of farnesyl iso prenoid moiety to the cysteine residue in the C-terminal box. Using a schis tosome extract in vitro SmRas farnesylation was inhibited by the farnesyl t ransferase inhibitor, FTI-277, at concentrations comparable to those requir ed to inhibit K-Ras processing. These initial studies on signal transductio n in schistosomes should provide a solid basis for improving our understand ing of schistosome-host interactions. (C) 1999 Elsevier Science B.V. All ri ghts reserved.