Family

Peptidase C1A, cathepsin K (IPR015644)

Short name: Peptidase_C1A_cathepsin-K

Family relationships

  • Peptidase C1A (IPR013128)
    • Peptidase C1A, cathepsin K (IPR015644)

Description

In the MEROPS database peptidases and peptidase homologues are grouped into clans and families. Clans are groups of families for which there is evidence of common ancestry based on a common structural fold:

  • Each clan is identified with two letters, the first representing the catalytic type of the families included in the clan (with the letter 'P' being used for a clan containing families of more than one of the catalytic types serine, threonine and cysteine). Some families cannot yet be assigned to clans, and when a formal assignment is required, such a family is described as belonging to clan A-, C-, M-, N-, S-, T- or U-, according to the catalytic type. Some clans are divided into subclans because there is evidence of a very ancient divergence within the clan, for example MA(E), the gluzincins, and MA(M), the metzincins.
  • Peptidase families are grouped by their catalytic type, the first character representing the catalytic type: A, aspartic; C, cysteine; G, glutamic acid; M, metallo; N, asparagine; S, serine; T, threonine; and U, unknown. The serine, threonine and cysteine peptidases utilise the amino acid as a nucleophile and form an acyl intermediate - these peptidases can also readily act as transferases. In the case of aspartic, glutamic and metallopeptidases, the nucleophile is an activated water molecule. In the case of the asparagine endopeptidases, the nucleophile is asparagine and all are self-processing endopeptidases.

In many instances the structural protein fold that characterises the clan or family may have lost its catalytic activity, yet retain its function in protein recognition and binding.

Cysteine peptidases have characteristic molecular topologies, which can be seen not only in their three-dimensional structures, but commonly also in the two-dimensional structures. These are peptidases in which the nucleophile is the sulphydryl group of a cysteine residue. Cysteine proteases are divided into clans (proteins which are evolutionary related), and further sub-divided into families, on the basis of the architecture of their catalytic dyad or triad [PMID: 11517925].

This group of cysteine peptidases belong to the MEROPS peptidase family C1, sub-family C1A (papain family, clan CA).

Cathepsin K is a cysteine protease expressed predominantly in osteoclasts. Activated cathepsin K cleaves key bone matrix proteins and is believed to play an important role in degrading the organic phase of bone during bone resorption. Cathepsin K is essential for normal bone resorption; Homo sapiens (Human) lacking cathepsin K exhibit pycnodysostosis, which is characterised by short stature and osteosclerosis [PMID: 14993931]. Histological and radiographic analysis of the cathepsin K-deficient Mus musculus (Mouse) revealed osteoporosis of the long bones and vertebrae, and abnormal joint morphology [PMID: 10491212].

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0008234 cysteine-type peptidase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PANTHER