Identification of a developmentally regulated Schistosoma mansoni serine protease homologous to mouse plasma kallikrein and human factor I

The isolation of 2 genomic clones has allowed us to further characterize a Schistosoma mansoni serine protease designated SmSP1. The deduced amino aci d sequence (248aa) considered as a 'light chain' encoding the active site, presents significant homologies with mouse plasma kallikrein and human fact or I light chain. The secondary structure of SmSP1 'light chain' is correct ly predicted and may be sufficient by itself to constitute an active enzyme . The biological function of SmSP1 is unknown, however, the homology with 2 serine proteases suggests that SmSP1 map play a role in the evasion of the host immune response. This is supported by the presence of the native prot ein corresponding to SmSP1 particularly in schistosomula released products (SRP) and in male dorsal spines. The expression of this enzyme is different ially regulated throughout the parasite life-cycle. However, infected anima ls with S. mansoni did not produce specific antibodies to recombinant SmSP1 . The lack of such response could be advantageous to the parasite by protec ting itself from host effector mechanisms.