Proteases are enzymes that catalyze the breakdown of proteins. Protein breakdown is a normal process necessary to maintain cellular homeostasis. Active proteases can be found throughout your body, including the digestive tract, inside cells and circulating in the blood.

Protein Structure

According to “Biochemistry: A Case-Oriented Approach,” amino acids serve as the building blocks of all proteins 1. Twenty different amino acids are used in various combinations to create all dietary and cellular proteins. At the most basic level, protein structure consists of amino acids linked together by a chemical bond called a peptide bond. Proteins can contain as few as one peptide bond to as many as several thousand.

Protease Function

According to “Biochemistry: A Case-Oriented Approach”, proteases catalyze proteolysis, an irreversible process that breaks down a protein to its component amino acids 1. Proteolysis cleaves the peptide bonds between amino acids in proteins. Free amino acids and smaller protein fragments are the products of protease activity.

Biological Roles

In the July 2003 edition of Nature Review Genetics, researchers say proteases are involved in many aspects of human biology. For example, in the small intestine, proteases digest dietary proteins to allow absorption of amino acids. Other processes mediated by proteases include:

• blood coagulation
  
• immune function
  
• maturation of prohormones
  
• bone formation
  
• programmed cell death
  
• the recycling of cellular proteins that are no longer needed

Protease Classification

Researchers estimate that humans are capable of producing more than 500 different proteases, which can be classified into five classes based on the mechanism by which the enzymes break peptide bonds. Aspartic and metallo-proteases use water to cleave peptide bonds. Cysteine, serine and threonine proteases catalyze proteolysis using mechanisms independent of water.

Proteases in Medicine

Many diseases can develop following overproduction of proteases. Therefore, a class of drugs called protease inhibitors has been developed to treat certain diseases and conditions. Examples of protease inhibitors in medicine include angiotensin converting enzyme inhibitors, to treat high blood pressure, and human immunodeficiency virus protease inhibitors, to treat HIV. Protease-based treatment is also being researched for use on other conditions, such as Alzheimer’s disease, Huntington’s disease, cancer and inflammatory disorders.