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Description

Cathepsin B (UniProt: P00787, also known as Cathepsin B1, RSG-2) is encoded by the Ctsb gene (Gene ID: 64529) in rat. Cathepsin B is a secreted lysosomal a lysosomal cysteine protease protease that is synthesized as a procathepsin with a signal peptide of 17 amino acids that directs it the lumen of rough endoplasmic reticulum where the signal peptide is removed to generate the inactive procathepsin B with a propeptide sequence. Procathepsin B is then transported to the Golgi apparatus where it is glycosylated at two asparagine residues by mannose containing oligosaccharides with phosphorylated mannose residues. The propeptide functions as an inhibitor and also stabilizes the enzyme. Procathepsin B is transported to lysosomes where under acidic conditions it undergoes autocatalytic activation following the removal of propeptide. Active cathepsin B is a dimer of a light chain and a heavy chain cross-linked by a disulfide bond. Cathepsin B hydrolyses proteins with broad specificity and preferentially cleaves Arg-Arg-|-Xaa bonds. In addition to being an endopeptidase, it also shows peptidyl-dipeptidase activity, liberating C-terminal dipeptides. Cathepsin B expression is elevated in several human cancers at the mRNA, protein, and activity levels. It is also frequently overexpressed in premalignant lesions. During the transition to malignancy, cathepsin B localizes to the cell periphery and at the basal pole of polarized cells and active cathepsin B is secreted from tumors and facilitates in invasion and metastasis. (Ref.: Aggarwal, N and Sloane, BF (2014) Proteomics Clin. Appl. 8, 427-437).