ABSTRACT
The
functions of the cathepsin B-like proteases in liver flukes are unknown
and analysis has been hindered by a lack of protein for study, since
the protein is produced in small amounts by juvenile flukes. To
circumvent this, we isolated and characterized a cDNA encoding the
major secreted cathepsin B from Fasciola hepatica. The
predicted preproprotein is 339 amino acids in length, with the mature
protease predicted to be 254 amino acids long, and shows significant
similarity to parasite and mammalian cathepsin B. Only one of the two
conserved histidine residues required for cathepsin B exopeptidase
activity is predicted to be present. Recombinant preproprotein was
produced in yeast, and it was shown that the recombinant proprotein can
undergo a degree of self-processing in vitro to the mature form, which
is active against gelatin and synthetic peptide substrates. The
recombinant protein is antigenic in vaccinated rats, and antibodies to
the protein are detected early after infection of rats and sheep with
F. hepatica. The kinetics of the response to cathepsin B and
cathepsin L after infection of sheep and rats confirm the temporal
expression of these proteins during the life cycle of the
parasite.