Definition of Serine Protease

Serine proteases are a class of enzymes that cut bonds between the amino acids that make up proteins. Serine proteases are important in digestion, blood clotting, and in the immune system.

Protease

• Proteases are enzymes that cleave proteins. Proteins consist of a series of amino acids each held to the next by a peptide bond. The active site of a protease recognizes its substrate (a specific protein formation), binds to it, and cuts the peptide bond. The cleavage can activate or inactivate the protein, depending on its type.

Serine Proteases

• Serine proteases are a family of proteases that all have the amino acid serine (abbreviated as Ser or S) in their active site. Serine is a hydroxylic amino acid and is hydrophilic ("water-loving").

Mechanism

• Serine proteases are sequence specific, meaning that they target only a particular pattern of amino acid linkages in their substrate proteins. They cleave their targets through a chemical reaction called hydrolysis, which involves the addition of water.

Roles

• The pancreas secretes three serine proteases that are important for digestion: chymotrypsin, trypsin, and elastase. Several factors that are critical for normal blood clotting--including Factor X which is often involved in hemophilia--are serine proteases. Serine proteases are also important to the complement component of the immune system.

Inhibition

• Serine proteases are controlled by a class of molecules called serpins, for serine protease inhibitors. Serpins trick serine proteases into binding them by imitating their normal substrates.