| Primary Identifier | IPR034224 | Type | Domain |
| Short Name | M14_CPD_II |
| description | This entry represents the second carboxypeptidase (CP)-like domain of carboxypeptidase D (CPD; EC 3.4.17.22; MEROPS M14.016).Carboxypeptidase D (CPD) differs from all other metallocarboxypeptidases in that it contains multiple CP-like domains []. CPD belongs to the N/E-like subfamily (subfamily M14B) of the M14 family of metallocarboxypeptidases (MCPs) []. CPD is a single-chain protein containing a signal peptide, three tandem repeats of CP-like domains separated by short bridge regions, followed by a transmembrane domain, and a C-terminal cytosolic tail. The first two CP-like domains of CPD contain all of the essential active site and substrate-binding residues, while the third CP-like domain lacks critical residues necessary for enzymatic activity and is inactive towards standard CP substrates. Domain I is optimally active at pH 6.3-7.5 and prefers substrates with C-terminal Arg, whereas domain II is active at pH 5.0-6.5 and prefers substrates with C-terminal Lys [, , ]. CPD functions in the processing of proteins that transit the secretory pathway, and is present in all vertebrates as well as Drosophila[]. It is broadly distributed in all tissue types. Within cells, CPD is present in the trans-Golgi network and immature secretory vesicles, but is excluded from mature vesicles []. It is thought to play a role in the processing of proteins that are initially processed by furin or related endopeptidases present in the trans-Golgi network, such as growth factors and receptors []. CPD is implicated in the pathogenesis of lupus erythematosus (LE), it is regulated by TGF-beta in various cell types of murine and human origin and is significantly down-regulated in CD14 positive cells isolated from patients with LE. As down-regulation of CPD leads to down-modulation of TGF-beta, CPD may have a role in a positive feedback loop [].The carboxypeptidase A family can be divided into four subfamilies: M14A(carboxypeptidase A or digestive), M14B (carboxypeptidase H or regulatory), M14C (gamma-D-glutamyl-L-diamino acid peptidase I) and M14D (AGTPBP-1/Nna1-like proteins) [, ]. Members of subfamily M14B have longer C-termini than those of subfamily M14A [], and carboxypeptidase M (a member of the H family) is bound to the membrane by a glycosylphosphatidylinositol anchor, unlike the majority of the M14 family, which are soluble []. The zinc ligands have been determined as two histidines and a glutamate,and the catalytic residue has been identified as a C-terminal glutamate,but these do not form the characteristic metalloprotease HEXXH motif [, ]. Members of the carboxypeptidase A family are synthesised as inactive molecules with propeptides that must be cleaved to activate the enzyme. Structural studies of carboxypeptidases A and B reveal the propeptide to exist as a globular domain, followed by an extended α-helix; this shields the catalytic site, without specifically binding to it, while the substrate-binding site is blocked by making specific contacts [, ]. |
