Proteases, as also called peptidases or proteinases, are enzymes that perform proteolysis. Proteolysis is one of the most important biological reactions. Proteolytic activity has been attributed to a class of enzymes called proteases. These enzymes are of wide distribution, and they perform significant biological processes. Proteases have evolved to perform these reactions by numerous different mechanisms and different classes of protease can perform the same reaction by completely different catalytic mechanisms. Proteases are found in animals, plants, bacteria, archaea, and viruses. Proteases are involved in protein processing, regulation of protein function, apoptosis, viral pathogenesis, digestion, photosynthesis, and numerous other vital processes. Proteases mechanism of action classifies them as either serine, cysteine or threonine proteases (amino-terminal nucleophile hydrolases), or as aspartic, metallo and glutamic proteases (with glutamic proteases being the only subtype not found in mammals so far).
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 and the recycling of cellular proteins that are no longer needed.
Proteases also offer a valuable target in many therapeutic settings, including Alzheimer's, cancer, and viral infection. MMP-9, a matrix metallopeptidase, plays a role in angiogenesis and is a therapeutic target for cancer. Because of their significance in the pathology of disease, proteases are a relevant drug target class. Proteases activity are central to diverse physiological cascades throughout biology. Some are essential for coagulation, while others contribute to cancer pathology.
Proteases can be classified into seven broad groups:
Serine proteases - using a serine alcohol, display a wide range of functions.
Cysteine proteases - using a cysteine thiol, that include caspases which are involved in apoptosis and inflammation, and cathepsins which promote protein degradation.
Threonine proteases - using a threonine secondary alcohol
Aspartic proteases - using an aspartate carboxylic acid, that include beta and gamma secretases, the two enzymes necessary to release amyloid beta peptides from the Alzheimer's disease associated amyloid precursor protein (APP).
Glutamic proteases - using a glutamate carboxylic acid
Metalloproteases - using a metal, usually zinc. The Metalloprotease family includes aminopeptidases and endopeptidases, which are secreted, membrane-bound, or cytosolic.
Asparagine peptide lyases - using an asparagine to perform an elimination reaction (not requiring water)