Carboxypeptidase E

Group II consists of the enkephalins which come from the 267-aniino acid piecuisoi pro-enkephalin A [88402-54-4] (Fig. 2). This proteia contains four copies of Met-enkephalin, one copy of Leu-enkephalin, and the extended peptides Met-enkephalin-Arg -Phe (the last Met-enkephalin sequence ia Fig. 2) and Met-enkephalin-Arg -Gly -Leu (the fourth Met-enkephalin sequence ia Fig. 2) (25,26). AH of these products ate formed by trypsin-like cleavage between pairs of basic residues. The extended enkephalin peptides are further cleaved by carboxypeptidase E (27) to form authentic Met-enkephalin. 

FIGURE 18-12 The/af//af mutation in carboxypeptidase E (CPE) leads to secretion of proinsulin, not mature insulin, and results in diabetes. The S202P mutation within CPE results in degradation of the enzyme and defective insulin processing in the fat/fat heterozygous mouse. LDCV, large dense-core vesicle. 

Figure 6.1 Characterization of impaired prohormone processing in mice lacking functional active carboxypeptidase E (Cpe mice) by peptidomics.

Fricker, L. D., Berman, Y. L, Leiter E. H., Devi, L. A. (1996). Carboxypeptidase E activity is deficient in mice with the fat mutation Effect on peptide processing. 

Figure 3 Cysteine protease and subtilisin-like protease pathways for proneuropeptide processing. Distinct cysteine protease and subtilisin-like protease pathways have been demonstrated for pro-neuropeptide processing. Recent studies have identified secretory vesicle cathepsin L as an important processing enzyme for the production of the endogenous enkephalin opioid peptide. Preference of cathepsin L to cleave at the NH2-terminal side of dibasic residue processing sites yields peptide intermediates with NH2-terminal residues, which are removed by Arg/Lys aminopeptidase. The well-established subtilisin-like protease pathway involves several prohormone convertases (PC). PC1/3 and PC2 have been characterized as neuroendocrine processing proteases. The PC enzymes preferentially cleave at the COOH-terminal side of dibasic processing sites, which results in peptide intermediates with basic residue extensions at their COOH-termini that are removed by carboxypeptidase E/H.

Significantly, the approach of activity profiling for cysteine proteases has established cathepsin L as a new protease pathway for neuropeptide biosynthesis. Together with current knowledge in the field, these data demonstrate the existence of two distinct protease pathways for converting proneuropeptides into active peptide neurotransmitters and hormones. These dual pathways consist of the newly discovered cysteine protease pathway for proneuropeptide processing, which consists of cathepsin L followed by Arg/Lys aminopeptidase (aminopeptidase B), and the previously known proprotein convertase (PC) family of subtilisin-like proteases (15-17) that process proneuropeptides with carboxypeptidase E (Fig. 3). Elucidation of these two protease pathways resulted from the application of the biochemical criteria required for processing proteases. 

After the actions of PCl/3 and PC2 for cleavage at the C-terminal side of paired basic residues (Fig. 3), the resulting peptide products contain basic residues at the C-termini that are then removed by carboxypeptidase E (CPE). Studies of ijjgj contain mutant, inactive CPE, showed that these animals show altered neuropeptide production (49-55). Studies of CPE peptide substrates in the fat/fat mice have been facilitated with specific isolation of peptides with C-terminal basic residues by the anhydrotrypsin affinity column for enrichment of CPE substrates (49-53). Analyses of such CPE substrates have demonstrated that numerous neuropeptides use CPE for their biosynthesis (49-55). 

Proteases are essential for the conversion of inactive proprotein precursors into the active neuropeptides. Two main protease pathways have been elucidated for processing proneuropeptides and hormones the recently discovered cysteine protease cathepsin L with aminopeptidase B and the well-established subtilisin-like serine proteases that consist of prohormone con-vertases 1 and 2 followed by carboxypeptidase E/H. Endogenous regulators modulate these two protease pathways as endogenous peptide inhibitors, activators, and in vivo secretory vesicle proteins. Neuropeptides in CSE (cerebrospinal fluid) in neurological diseases can monitor brain nervous activity because neuropeptides represent active neurotransmission (93, 94). 

Cool DR, Normant E, Shen F, Chen HC, Pannell L, Zhang Y, Loh YP. Carboxypeptidase E is a regulated secretory pathway sorting receptor genetic obliteration leads to endocrine disorders in Cpe(fat) mice. Cell 1997 88 73-83. 

Figure 8.7. The two-step reaction of inhibition of transpeptidase and carboxypeptidase (E) by p-lactam antibiotics (A), according to the structural analogue model...

Agouti Gene and Agouti Protein Melanocortin Receptors Proposed Feedback Loop Fat Gene and Carboxypeptidase E Tubby Gene Summary References Bibliography... 

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