Protease
An enzyme that cleaves peptide bonds, breaking down peptides and proteins into smaller fragments. Proteases are found throughout the body — in the blood, digestive tract, and within cells — and are the main reason most natural peptides have very short half-lives.
Technical Context
Proteases (also called peptidases or proteinases) are classified by their catalytic mechanism: serine proteases (e.g. trypsin, chymotrypsin, DPP-4), cysteine proteases (e.g. caspases), aspartic proteases (e.g. pepsin, renin), metalloproteases (e.g. matrix metalloproteinases, angiotensin-converting enzyme), and threonine proteases (the proteasome's catalytic subunits). DPP-4 is a serine protease of particular importance in peptide therapeutics because it rapidly degrades GLP-1 and GIP. Understanding which proteases degrade a specific therapeutic peptide enables rational design of resistant analogues. Protease inhibitors (e.g. bortezomib, carfilzomib) are themselves therapeutic agents targeting the proteasome.