Carboxypeptidase E, carboxypeptidase domain (IPR034232)

Short name: M14_CPE_CPD

Overlapping homologous superfamilies


Domain relationships


This entry represents the carboxypeptidase domain found in carboxypeptidase (CP) E (CPE, also known as carboxypeptidase H, and enkephalin convertase;(EC:; MEROPS identifier M14.005). CPE belongs to subfamily M14B (N/E subfamily) of the M14 family of metallocarboxypeptidases (MCPs) [PMID: 7674922]. It is an important enzyme responsible for the proteolytic processing of prohormone intermediates (such as pro-insulin, pro-opiomelanocortin, or pro-gonadotropin-releasing hormone) by specifically removing C-terminal basic residues [PMID: 10966857]. In addition, it has been proposed that the regulated secretory pathway (RSP) of the nervous and endocrine systems utilizes membrane-bound CPE as a sorting receptor. A naturally occurring point mutation in CPE reduces the stability of the enzyme and causes its degradation, leading to an accumulation of numerous neuroendocrine peptides that result in obesity and hyperglycemia [PMID: 10500303, PMID: 7663508]. Reduced CPE enzyme and receptor activity could underlie abnormal placental phenotypes from the observation that CPE is down-regulated in enlarged placentas of interspecific hybrid (interspecies hybrid placental dysplasia, IHPD) and cloned mice [PMID: 17177860].

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) [PMID: 7674922, PMID: 17244818]. Members of subfamily M14B have longer C-termini than those of subfamily M14A [PMID: 1449602], 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 [PMID: 7674922]. 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 [PMID: 7674922, PMID: 6887246]. 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 alpha-helix; this shields the catalytic site, without specifically binding to it, while the substrate-binding site is blocked by making specific contacts [PMID: 7674922, PMID: 1548696].

Contributing signatures

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