Protease refers to a group of enzymes whose catalytic function is to hydrolyze peptide bonds of proteins. They are also called proteolytic enzymes or proteinases. Proteases differ in their ability to hydrolyze various peptide bonds. Proteases also have many functions. The action of proteases was believed to be restricted to digestive purposes, extracellular modeling and/or remodeling of tissues, mainly through proteolytic activity on interstitial molecules, occurring throughout homeostasis and development or, in aberrant maladaptive circumstances, during disease pathogenesis.
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 are not merely restricted to digestive purposes and remodeling of extracellular matrix and tissues, but are also key factors for the induction of physiological immune responses. This induction can be direct, through the degradation of pathogens within phagolysosomes, or indirect, through the activation of key pattern recognition receptors (PRRs), such as toll-like receptors (TLRs). Unfortunately, excess production of proteases leads to maladaptive host responses and excess tissue inflammation and damage.
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.