Proteinase

Proteinase (also known as a protease or peptidase) is a type of enzyme that performs proteolysis. Proteolysis is the breakdown of proteins into smaller polypeptides or single amino acids. This is achieved by the hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein.

Proteinases have evolved multiple times, and different classes of proteinase can perform the same reaction by completely different catalytic mechanisms. Proteinases can be found in all living organisms, from viruses to humans. They are involved in a multitude of physiological reactions from simple digestion of food proteins to highly regulated cascades (e.g., the blood clotting cascade, the complement system, apoptosis pathways, and the invertebrate prophenoloxidase activating cascade).

Proteinases can either break specific peptide bonds (limited proteolysis), depending on the amino acid sequence of a protein, or break down a complete peptide to amino acids (unlimited proteolysis). The activity can be a destructive change, abolishing a protein's function or digesting it to its principal components; it can be an activation of a function, or it can be a signal in a signaling pathway.

Classification

Proteinases are classified by the catalytic type of the active site. The four main types are:

• Serine proteinases
• Cysteine proteinases
• Aspartic proteinases
• Metalloproteinases

Function

Proteinases play key roles in many biological functions, including:

• Digestion of ingested proteins
• Cell cycle regulation
• Apoptosis (programmed cell death)
• Immune response
• Blood coagulation
• Protein synthesis
• Cell signaling
• Protein recycling

See also

• Enzyme
• Proteolysis
• Peptide bond
• Amino acid
• Polypeptide

Proteinase Resources
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