CTSZ is a lysosomal cysteine proteinase and member of the peptidase C1 family. It exhibits both carboxy-monopeptidase and carboxy-dipeptidase activities. The protein has also been known as cathepsin X and cathepsin P. This gene is expressed ubiquitously in cancer cell lines and primary tumors and, like other members of this family, may be involved in tumorigenesis. At least two transcript variants of this gene have been found, but the full-length nature of only one of them has been determined. Recombinant human CTSZ protein, fused to His-tag at N-terminus, was expressed in E.coli .