Cathepsins are proteases found in all animals as well as other organisms. There are approximately a dozen members of this family, which are distinguished by their structure, catalytic mechanism, and which proteins they cleave. Most of the members become activated at the low pH found in lysosomes. Thus, the activity of this family lies almost entirely within those organelles. There are, however, exceptions such as cathepsin K, which works extracellularly after secretion by osteoclasts in bone resorption. Cathepsins have a vital role in mammalian cellular turnover.
Cathepsin S is a protein that in humans is encoded by the CTSS gene. Transcript variants utilizing alternative polyadenylation signals exist for this gene.
Cathepsin O is an enzyme encoded by the CTSO gene in humans.
Cathepsin K, abbreviated CTSK, is an enzyme that in humans is encoded by the CTSK gene.
Cathepsin L1 is a protein that in humans is encoded by the CTSL1 gene. The protein is a cysteine cathepsin, a lysosomal cysteine protease that plays a major role in intracellular protein catabolism.
Cystatin-A is a protein that in humans is encoded by the CSTA gene.
Cystatin-B is a protein that in humans is encoded by the CSTB gene.
Serpin B3 is a protein that in humans is encoded by the SERPINB3 gene.
Cathepsin H is a protein that in humans is encoded by the CTSH gene.
Caspase 14 is an enzyme that in humans is encoded by the CASP14 gene. Orthologs of this gene also exist in other mammals, such as sirenians and cetaceans, though they are inactivated in these two clades. Curiously, manatees, which are sirenians, retain some functional CASP14 genes.
Cystatin-SA is a protein that in humans is encoded by the CST2 gene.
Cystatin-M is a protein that in humans is encoded by the CST6 gene.
Cathepsin L2 is a protein encoded in humans by the CTSV gene.
Ubiquitin specific protease 4 (USP4) is an enzyme that cleaves ubiquitin from a number of protein substrates. Prior to the standardization of nomenclature USP4 was known as UNP, and was one of the first deubiquitinating enzymes to be identified in mammals. In the mouse and human the USP4 protein is encoded by a gene containing 22 exons.
Ubiquitin-specific protease 36 is an enzyme that in humans is encoded by the USP36 gene.
Serpin B13 is a protein that in humans is encoded by the SERPINB13 gene.
Tubulointerstitial nephritis antigen-like is a protein that in humans is encoded by the TINAGL1 gene.
Calpain-5 is a protein that in humans is encoded by the CAPN5 gene.
Cathepsin F is a protein that in humans is encoded by the CTSF gene.
WAP four-disulfide core domain protein 5 is a protein that in humans is encoded by the WFDC5 gene.
