Carboxypeptidase E
Carboxypeptidase E, also known as carboxypeptidase H and enkephalin convertase, is an enzyme that in humans is encoded by the CPE gene.[1][2]
Carboxypeptidase E is found in brain and throughout the neuroendocrine system, including the endocrine pancreas, pituitary, and adrenal gland chromaffin cells. Within cells, carboxypeptidase E is present in the secretory granules along with its peptide substrates and products. Carboxypeptidase E is a glycoprotein that exists in both membrane-associated and soluble forms. The membrane-binding is due to an amphiphilic α-helix within the C-terminal region of the protein. Carboxypeptidase E is found in all species of vertebrates that have been examined, and is also present in many other organisms that have been studied (nematode, sea slug). Carboxypeptidase E is not found in the fruit fly (Drosophila), and another enzyme (presumably carboxypeptidase D) fills in for carboxypeptidase E in this organism.
Carboxypeptidase E functions in the production of nearly all neuropeptides and peptide hormones. The enzyme acts as an exopeptidase to activate neuropeptides. It does that by cleaving off basic C-terminal amino acids, producing the active form of the peptide. Products of carboxypeptidase E include insulin, enkephalin, vasopressin, oxytocin, and most other neuroendocrine peptide hormones and neuropeptides.
It has been proposed that membrane-associated carboxypeptidase E acts as a sorting signal for regulated secretory proteins in the trans-Golgi network of the pituitary and in secretory granules; regulated secretory proteins are mostly hormones and neuropeptides. However, this role for carboxypeptidase E remains controversial, and evidence shows that this enzyme is not necessary for the sorting of regulated secretory proteins.
Mice with mutant carboxypeptidase E, Cpefat, display endocrine disorders like obesity and infertility. In some strains of mice, the fat mutation also causes hyperproinsulinemia in adult male mice, but this is not found in all strains of mice. The obesity and infertility in the Cpefat mice develop with age; young mice (<8 weeks of age) are fertile and have normal body weight. Peptide processing in Cpefat mice is impaired, with a large accumulation of peptides with C-terminal lysine and/or arginine extensions. Levels of the mature forms of peptides are generally reduced in these mice, but not completely eliminated. It is thought that a related enzyme (carboxypeptidase D) also contributes to neuropeptide processing and gives rise to the mature peptides in the Cpefat mice.
See also
References
- ^ Manser E, Fernandez D, Loo L, Goh PY, Monfries C, Hall C, Lim L (1990). "Human carboxypeptidase E. Isolation and characterization of the cDNA, sequence conservation, expression and processing in vitro". Biochem J. 267 (2): 517–25. PMC 1131319. PMID 2334405.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ "Entrez Gene: CPE carboxypeptidase E".
Further reading
External links
- The MEROPS online database for peptidases and their inhibitors: M14.005
- Carboxypeptidase+E at the U.S. National Library of Medicine Medical Subject Headings (MeSH)