Isolation of a cDNA encoding Fasciola hepatica cathepsin L2 and functional expression in Saccharomyces cerevisiae

Cathepsin L2 is a major cysteine proteinase secreted by adult Fasciola hepatica. The enzyme differs from other reported cathepsin Ls in that it can cleave peptide substrates that contain proline in the P₂ position. A cDNA was isolated from an expression library by immunoscreening with antiserum prepared against purified native cathepsin L2. This cDNA was sequenced and shown to encode a complete preprocathepsin L proteinase. Functionally active recombinant cathepsin L proteinase was expressed and secreted by Saccharomyces cerevisiae transformed with the cDNA. The recombinant enzyme was purified from large-scale fermentation broths using ultrafiltration and gel filtration chromatography on Sephacryl S200 HR columns. NH₂-terminal amino acid sequencing showed that the cleavage point for activation of the recombinant pro-enzyme is identical to that of the F. hepatica-produced cathepsin L2. The mature active recombinant proteinase behaved similarly to the native enzyme when analyzed by SDS-PAGE, immunoblotting and zymography and also cleaved peptides containing proline in the P₂ position. Finally, the recombinant cathepsin L2 cleaved fibrinogen to form a fibin clot, a property we described for F. hepatica cathepsin L2.