Molecular cloning and analysis of stage and tissue-specific expression of Cathepsin L-like protease from Clonorchis sinensis

Cathepsin L of parasite plays multiple roles in growth, food uptake, and invasion into host and pathogenesis, which makes it a valuable target for diagnosis, vaccine, and drug. In this study, we identified a cDNA encoding cathepsin L homolog (CsCPL) from the library of Clonorchis sinensis adult by bioinformatics analysis. Sequence encoding proenzyme of CsCPL (removal of signal peptide, CsproCPL) was highly expressed in form of inclusion body in Escherichia coli, and soluble rCsproCPL (about 1 mg/ml) in high purity were obtained after denaturation, purification, and renaturation. Western blot analysis indicated that CsCPL is a component of excretory-secretory products of adult, in mature form of protease. Reverse transcription polymerase chain reaction showed that CsCPL is also expressed in metacercaria and cercaria stage. Immunolocalization demonstrated that CsCPL is deposited at adult intestine, or tegument, and tegumentary cell of metacercaria and cercaria (especially at dorsal tegument of cercaria), indicating different secretory routine roles in adult and larva. The characteristics of CsCPL suggested that it may involve in invasion of cercaria into fish and development to metacercaria, excystment of metacercaria, and protein digestion of adult, which may render it a candidate antigen for fish vaccine and serodiagnosis of human clonorchiasis.