Cathepsin B Substrate

Cathepsin B, a bilobal protein, belongs to the papain-like family of cysteine proteases. It is produced as a preproenzyme. Its catalytic site is present at the interface between the two lobes. Cathepsin B has an occluding loop. It is located in the secretory vesicles of the neuronal cells. Active cathepsin B is found in the endosomal or lysosomal compartment under normal physiological conditions.

Cathepsin B is a lysosomal cysteine proteinase that metabolizes important molecules such as β-amyloid precursor protein into harmless fragments. Cathepsin B may be detected using the chromogenic substrate Z-Arg-Arg-pNA (z-arg-arg-p-nitroanalide) or flourogenic substrate Z-Arg-Arg-AMC (z-Arg-Arg-amino-4-methylcoumarin).

Cathepsin B possesses endopeptidase and exopeptidase activity. Active cathepsin B is mostly engaged in intracellular and extracellular protein turnover, which helps cells maintain homeostatic metabolic activity. It also participates in the regulation of pro-hormone and pro-enzyme activation, antigen processing, inflammatory reactions against antigens, tissue remodeling, and apoptosis. Cathepsin B plays a key role in acute pancreatitis. It also plays a vital role in lipid metabolism in atherosclerosis.