Cathepsin B of Schistosoma mansoni. Purification and activation of the recombinant proenzyme secreted by Saccharomyces cerevisiae.

Procathepsin B from the parasitic trematode Schistosoma mansoni was expressed as a glycosylation-minus mutant in yeast cells and purified by means of a histidine affinity tag which was added to the carboxyl terminus of the recombinant protein. The purified zymogen underwent autoprocessing but required an assisting protease for activation. Pepsin-activated schistosomal cathepsin B was further characterized with the cathepsin B-specific substrates N-benzyloxycarbonyl (Z)-Arg-Arg-p-nitroanilide, Z-Arg-Arg-7-amido-4-methyl-coumarin, and Z-Phe-Arg-7-amido-4-methylcoumarin. A proteolytic activity comparable to mammalian cathepsin B was observed. In addition, we analyzed the degradation of human hemoglobin by schistosomal cathepsin B, which has been suggested to be the physiological target of the protease.