What Are the Functions of Serine Protease?

Serine proteases are enzymes that cleave (cut up) proteins. They are particularly important for digestion and blood clotting, and in the immune system.

Mechanism

• Serine proteases have the amino acid serine in their active site, where the protease binds its target protein. Serine is a hydroxylic, hydrophilic ("water-loving") amino acid. When a serine protease binds to its substrate, a chemical reaction called hydrolysis (the chemical addition of water) cleaves the protein between two specific amino acids.

Digestion

• The pancreas secretes three serine proteases that are critical for normal digestion: trypsin, chymotrypsin and elastase. Trypsin not only digests proteins, it also activates the other serine proteases chymotrypsin and elastase by cleaving their inactive precursors, called zymogens, into their active forms.

Blood Clotting

• Several important factors in the cascade of reactions that leads to blood clotting are serine proteases. Hemophiliacs often have defective serine protease activity in blood clotting. The serine protease thrombin is critical both to clot formation and to limiting the size of a blood clot.

Immune Function

• The complement cascade, part of the immune system, is a series of enzyme reactions that helps to prevent infection. Serine proteases operate at many steps in the complement cascade.

Control

• Serine proteases are controlled serpins (serine protease inhibitors). Serpins inhibit serine proteases by mimicking their normal substrates.