Cathepsin B (pro) (CTSB)
Cathepsin B (CTSB) is a normal lysosomal proteinase that is expressed in all cells. It is a cysteine endoproteinase structurally and functionally related to the papain family of proteases. CTSB is synthesized as an inactive 43 kDa pro enzyme which, by removal of a 62 amino acid propeptide, is activated to the single chain form of 31 kDa or the two chain form (25 and 5 kDa subunits). Matured CTSB is normally localized in the lysosomes where it functions in protein turnover. In tumor cells and in cells exposed to mitogens, CTSB displays altered cellular trafficking resulting in the secretion of the 43 kDa precursor. Elevated levels of CTSB correlate with malignancy suggesting that this enzyme may be a useful prognostic marker for several types of human cancers. CTSB has also been implicated in the pathogenesis of rheumatoid arthritis, muscular dystrophy and tumor metastasis.
Swiss-Prot Accession Number: P07858