Immunochemical studies on the cercarial-specific calcium binding protein of Schistosoma mansoni

Stage-specific expression of the mRNA encoding the cercarial-specific 8 kDa CaBP has been described previously. To gain information on possible function(s) of this protein we raised antibodies to the CaBP in rabbits immunized with a CaBP-TrpE fusion protein synthesized in bacteria. Western blots showed high levels of CaBP in cercariae and 3 h schistosomula, trace amounts in 24 h schistosomula, and none in miracidia sporocyst and adult worm, as found for the mRNA. The CaBP molecule has a short half-life (< or = 4 h) similar to that of the mRNA. Other experiments demonstrate that the CaBP may interact with a putative target molecule in a calcium-dependent manner to form a complex of 45 kDa. Immunogold electron microscopy showed CaBP in selected regions of cercariae and 3 h schistosomula: tegument, head gland, subtegumental cells, flame cells, intestinal wall and the body-tail junction. Other investigators have shown that the head gland and subtegumental cells synthesize and translocate granules to the tegument during transformation from cercariae (living freely in water) to schistosomula (residing in vertebrate host). These observations and the time-course of CaBP detection suggest that the CaBP synthesized in the head gland and subtegumental cells is translocated to the tegument where it plays a role in tegument modifications required for adaptation to parasite life in the host. CaBP was not found in muscles and mitochondria, suggesting that it is not involved in the rapid motility and aerobic metabolism characteristic of cercariae.