A PCR strategy using degenerate oligonucleotide primers based upon
consensus sequences of the active site of serine
proteases yielded a 467 bp fragment from genomic DNA from
Schistosoma mansoni cercariae. The sequence presented a
continuous open reading frame and the deduced amino acid sequence (156
aa)
presented homologies with various serine
proteases, in particular the highest percentage identity was observed with
a mammalian plasma kallikrein. The expression
of this serine protease was studied first at the mRNA level and it was
only
detected by RT-PCR in cercariae and in adult
worms. At the protein level we were able to detect it by Western blotting
and by using antigen extracts from metabolically
radio-isotope labelled worms. The absence of any positive signal in
Northern blot and the detection of the protein suggest
that the mRNA has a very short half-life, however the protein may be
accumulated in the parasite. The significance of
identity with mammalian kallikrein was confirmed by cross-immunoreactivity
with a native porcine pancreatic kallikrein.
However, no cross-reactivity was observed with S. mansoni
elastase, another serine protease. Thus, we suggest that the
serine protease described in this paper is a kallikrein-like protease.
Characterization of a Partial Sequence Encoding Envelop Protein of HCV-Genotype 4a Egyptian Isolate
