CTSB determined the crystal structure of the human being, since studies on cathepsin rapid development, rapid progress. Proteinase (protease) are a class of proteins catalyze the hydrolysis of peptide bonds enzymes, belonging to six categories hydrolase enzymes. Hydrolysis of the polypeptide according to the method can be divided into exopeptidases endopeptidase enzyme, wherein the enzyme but also according to the outer end of the peptide when the peptide bond hydrolysis is divided into different origin aminopeptidase and carboxypeptidase; protease activity according to the groups of different catalytic properties of the center, which can be divided into E-64 serine proteases (serine protease), threonine protease (threonine protease), cysteine protease (cysteine protease), aspartic proteases (aspartic protease) and metalloprotease (metalloprotease) and the like; protease according to the optimal reaction pH values, can be divided into the acid protease, neutral protease and alkaline protease. Many proteases, cysteine proteases are more relevant research, which is widely present in the organism, such as bacteria, viruses, plants, lower and higher animals, including parasites, variety. This class contains a protease active site cysteine residue essential and depends on it catalyzes the hydrolysis of peptide bonds mercapto group, it is also referred to as thiol proteases (thiol protease).