Peptidase M14 carboxypeptidase subfamily N/E-like; Carboxypeptidase D, domain I subgroup
The first carboxypeptidase (CP)-like domain of Carboxypeptidase D (CPD; EC 3.4.17.22), domain I. CPD differs from all other metallocarboxypeptidases in that it contains multiple CP-like domains. CPD belongs to the N/E-like subfamily of the M14 family of metallocarboxypeptidases (MCPs).The M14 family are zinc-binding CPs which hydrolyze single, C-terminal amino acids from polypeptide chains, and have a recognition site for the free C-terminal carboxyl group, which is a key determinant of specificity. 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, 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. This Domain I family contains two contiguous surface cysteines that may become palmitoylated and target the enzyme to membranes, thus regulating intracellular trafficking. 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. In D. melanogaster, the CPD variant 1B short (DmCPD1Bs) is necessary and sufficient for viability of the fruit fly.
Comment:Metallocarboxypeptidases share the zinc binding motif HXXE...H, where the zinc ion is penta-coordinated to ND1 atoms of the histidines, OE1 and OE2 atoms of the glutamic acid, and to a water molecule in a slightly distorted tetrahedral manner.
Structure:3MN8: Drosophila melanogaster carboxypeptidase D isoform 1B bound to a zinc ion; contacts at 4.0A - View structure with Cn3D
Jiyao W et al.(2023). "The conserved domain database in 2023.",