Cysteine proteases (CPs) are responsible for many biochemical processes occurring in living organisms and they have been implicated in the development and progression of several diseases that involve abnormal protein turnover. The main physiological role of Cysteine proteases is metabolic degradation of peptides and proteins. The activity of Cysteine proteases is regulated among others by their specific inhibitors: cystatins.
Cysteine proteases play multi-faceted roles, virtually in every aspect of physiology and development. Cysteine proteases are responsible for senescence and apoptosis, MHC class II immune responses, prohormone processing, and extracellular matrix remodeling important to bone development. The ability of macrophages and other cells to mobilize elastolytic cysteine proteases to their surfaces under specialized conditions may also lead to accelerated collagen and elastin degradation at sites of inflammation in diseases such as atherosclerosis and emphysema. Several viruses express their entire genome as a singe massive polyprotein and use a protease to cleave it into functional units.
As the two major families of cysteine proteases, Caspases are cytosolic, asparate-specific and involved in apoptosis whereas Cathepsins are mainly lysosomal, active under acidic conditions and involved in protein degradation. Legumain and Separase are two newer proteases with the specificity for Asn residue and Cohesin, respectively. Known protein inhibitors of the cysteine proteases are members of Cystatin, IAP, Testican and Lipocalin families.
Other Cysteine Protease Regulators