Protease

A protease (also known as a peptidase or proteinase) is an enzyme that catalyzes proteolysis – the breakdown of proteins into smaller polypeptides or single amino acids. This is achieved by cleaving the peptide bonds between amino acids within a protein through hydrolysis, a reaction where water is used to break a chemical bond.

Proteases are ubiquitous and found in all forms of life and viruses. They are involved in a multitude of physiological processes, including:

• Digestion: Breaking down dietary proteins into absorbable amino acids.
• Cell signaling: Activation or inactivation of signaling molecules.
• Immune response: Complement activation, antigen processing, and antibody production.
• Blood clotting: Formation and dissolution of blood clots.
• Apoptosis: Programmed cell death.
• Protein turnover: Degradation of misfolded or damaged proteins.
• Viral replication: Processing of viral polyproteins into functional proteins.

Proteases are classified based on their catalytic mechanism. The five major classes are:

• Serine proteases: Characterized by a serine residue in their active site.
• Cysteine proteases: Utilize a cysteine residue for catalysis.
• Aspartic proteases: Employ two aspartic acid residues in their active site.
• Metalloproteases: Require a metal ion, usually zinc, for activity.
• Threonine proteases: Utilize a threonine residue for catalysis.

Proteases are also classified by their site of action on the protein substrate:

• Exopeptidases: Cleave amino acids from the ends of polypeptide chains. These are further subdivided into aminopeptidases (cleaving from the N-terminus) and carboxypeptidases (cleaving from the C-terminus).
• Endopeptidases: Cleave peptide bonds within the polypeptide chain.

Due to their diverse functions, proteases are of significant interest in various fields, including medicine, biotechnology, and food science. Inhibitors of proteases are used as drugs to treat various diseases, such as HIV infection and hypertension. In biotechnology, proteases are used in a variety of applications, such as protein sequencing and peptide synthesis.