Seriinproteaaside

Seriinproteaasid, also known as serine proteases, are a broad family of proteolytic enzymes characterized by a serine residue in the catalytic site that initiates peptide bond cleavage. They function in digestion, blood coagulation, immune defense, and tissue remodeling, among other processes. The canonical mechanism involves a catalytic triad of serine, histidine, and aspartate. The serine residue acts as a nucleophile, histidine serves as a base to activate serine, and aspartate stabilizes histidine. Substrate binding promotes formation of a tetrahedral intermediate; an acyl-enzyme intermediate is formed and subsequently hydrolyzed by water to release products. An oxyanion hole stabilizes the transition state.

Most well-known serine proteases belong to the chymotrypsin-like (S1) family, which has two beta-barrel domains and a deeply buried catalytic triad. Common examples include trypsin, chymotrypsin, and elastase from the digestive system, as well as thrombin, factor Xa, plasmin, and other proteases in the coagulation and fibrinolytic pathways. Other serine proteases include subtilisin-like enzymes from bacteria and archaea, which have distinct structural folds but share the same catalytic strategy.

Serine proteases are tightly regulated by inhibitors such as serpins; uncontrolled activity can cause tissue damage. Therapeutically, they are targets for anticoagulants and anti-inflammatory agents, and industrially they are used in detergents and specialized biocatalysis.