proteinase

Proteinase, or protease, is an enzyme that catalyzes proteolysis, the breaking of peptide bonds in proteins. Proteases are diverse in sequence and structure but share the ability to hydrolyze peptide bonds and are classified by their catalytic mechanism into serine, cysteine, aspartic, metalloproteases, threonine, and glutamic proteases. They can act as endopeptidases, cleaving within polypeptides, or exopeptidases, trimming terminal amino acids. Many proteases are produced as inactive precursors (zymogens) and require activation.

Key protease groups include serine proteases (for example trypsin and chymotrypsin), aspartic proteases (pepsin), cysteine proteases (papain, caspases), metalloproteases (matrix metalloproteinases), and proteasomal threonine proteases. Activation typically involves structural rearrangements or cleavage of inhibitory segments. Activity is often regulated by inhibitors, pH, subcellular location, and cofactors such as metal ions or reducing environments.

Proteases play essential roles in digestion, protein turnover, and activation of signaling pathways. In humans, proteases participate in digestion (salivary and pancreatic proteases), blood coagulation and fibrinolysis (serine proteases like thrombin), immune responses, and apoptosis (caspases). Matrix metalloproteinases remodel extracellular matrix, influencing development and wound healing. Aberrant protease activity is linked to diseases such as pancreatitis, cancer invasion, and neurodegeneration; therapeutic strategies include protease inhibitors.

Proteases have widespread applications in industry and research. Industrial uses include detergents, food processing, leather treatment, and pharmaceutical manufacturing. In the lab, proteases are used to digest proteins for analysis, to activate prodrugs, and in the study of protein structure and turnover. Examples of clinically important protease inhibitors include those targeting viral or host proteases to treat infections or coagulation disorders.