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 that in humans is encoded by the CTSO gene.
Cathepsin B belongs to a family of lysosomal cysteine proteases known as the cysteine cathepsins and plays an important role in intracellular proteolysis. In humans, cathepsin B is encoded by the CTSB gene. Cathepsin B is upregulated in certain cancers, in pre-malignant lesions, and in various other pathological conditions.
Cathepsin D is a protein that in humans is encoded by the CTSD gene. This gene encodes a lysosomal aspartyl protease composed of a protein dimer of disulfide-linked heavy and light chains, both produced from a single protein precursor. Cathepsin D is an aspartic endo-protease that is ubiquitously distributed in lysosomes. The main function of cathepsin D is to degrade proteins and activate precursors of bioactive proteins in pre-lysosomal compartments. This proteinase, which is a member of the peptidase A1 family, has a specificity similar to but narrower than that of pepsin A. Transcription of the CTSD gene is initiated from several sites, including one that is a start site for an estrogen-regulated transcript. Mutations in this gene are involved in the pathogenesis of several diseases, including breast cancer and possibly Alzheimer disease. Homozygous deletion of the CTSD gene leads to early lethality in the postnatal phase. Deficiency of CTSD gene has been reported an underlying cause of neuronal ceroid lipofuscinosis (NCL).
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.
Cathepsin H is a protein that in humans is encoded by the CTSH gene.
Cystatin-SN is a protein that in humans is encoded by the CST1 gene.
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.
Cystatin-F is a protein that in humans is encoded by the CST7 gene.
Cystatin-D is a protein that in humans is encoded by the CST5 gene.
Cathepsin Z, also called cathepsin X or cathepsin P, is a protein that in humans is encoded by the CTSZ gene. It is a member of the cysteine cathepsin family of cysteine proteases, which has 11 members. As one of the 11 cathepsins, cathepsin Z contains distinctive features from others. Cathepsin Z has been reported involved in cancer malignancy and inflammation.
Cathepsin L2 is a protein encoded in humans by the CTSV gene.
Cathepsin W is a protein that in humans is encoded by the CTSW gene.
Tubulointerstitial nephritis antigen-like is a protein that in humans is encoded by the TINAGL1 gene.
Cystatin-9-like is a protein that in humans is encoded by the CST9L gene.
Papain-like proteases are a large protein family of cysteine protease enzymes that share structural and enzymatic properties with the group's namesake member, papain. They are found in all domains of life. In animals, the group is often known as cysteine cathepsins or, in older literature, lysosomal peptidases. In the MEROPS protease enzyme classification system, papain-like proteases form Clan CA. Papain-like proteases share a common catalytic dyad active site featuring a cysteine amino acid residue that acts as a nucleophile.
