Metallocarboxypeptidases

Abstract

Metallocarboxypeptidases (CP) catalyze the removal of C‐terminal amino acids from proteins and/or peptides. The different members of the CP family differ in their specificity for C‐terminal residues and physiological function and can be divided into two subfamilies. Members of the A/B subfamily are generally produced as proenzymes, contain an approximately 300‐residue CP catalytic domain, have greatest amino acid sequence identity to the exocrine pancreatic enzymes CPA and CPB, and prefer hydrophobic or basic residues. They function in the breakdown of peptides in food or in other physiological processes ranging from inflammation to fibrinolysis. Members of the N/E group cleave C‐terminal basic residues and are not produced as inactive proenzymes but contain an approximately 80‐residue region following the 300‐residue CP domain with structural homology to transthyretin. They act either extra‐ or intracellularly in the processing of peptide hormones and neurotransmitters and other physiologically relevant peptides. The tertiary folding of CPs corresponds to the α/β hydrolase fold and is formed by a central mixed parallel/antiparallel eight‐strand β‐sheet, with a 120° twist between the first and the last strand, over which eight α‐helices pack on both sides to form a globular molecule. All of the enzymatically active CPs bind one atom of Zn 2+ at the active site. Some members of the CP family that are inactive against standard CP substrates lack some of the cation‐binding ligands and may therefore not be able to bind the metal.

A novel metallocarboxypeptidase‐like enzyme from the marine annelid Sabellastarte magnifica– a step into the invertebrate world of proteases

“…A central question in the analysis of novel MCPs from biological sources is whether they occur in their precursor or mature forms [2–5]. In the present study, using direct extracts from S. magnifica , we found only a monomeric and activated form of SmCP, as shown by its enzymatic activity, molecular mass, derived N‐terminal sequence and homology analysis.…”

“…Again, the addition of rPCI prevented any kind of hydrolysis by the enzyme. The release of a glutamic acid residue from the C‐terminus of peptides is a very unusual capability of a CPA‐like enzyme and is reminiscent of the so‐called CPO forms [3,5].…”

“…Very recently, a novel subfamily composed of enzymes of larger size and apparently with a predominant cytosolic location, termed M14D, Nna‐like or CCPs, has been proposed [4]. Furthermore, three main classes may be distinguished according to their substrate specificity: (a) for aromatic/hydrophobic residues (A‐like), (b) for basic residues (B‐like) and (c) for acidic residues (O‐like) [3,5].…”

“…MCP enzymes have been isolated from different sources [3,5,6], mainly from vertebrates, but a few of them have come from marine invertebrate organisms: the digestive crayfish carboxypeptidase (CPB) [7], the carboxypeptidase E‐like enzyme from the sea hare Aplysia californica , with important regulatory functions in this organism [8], two CPs (A and B types) from the hepatopancreas of the crab Paralithodes camtschatica [9], the CPA‐like protease from squid hepatopancreas of Illex illecebrosus [10], and CPs (two A and one B type) isolated from the pyloric ceca of the starfishes Asterias amurensis [11,12] and Asterina pectinifera [13].…”

“…From this, it is apparent that SmCP is a novel M14 MCP (belonging to the pancreatic‐like subfamily), showing simultaneous CPA‐ and CPO‐like activities, which is an unusual feature. The present study comprises an attempt to expand the growing field of the M14 family of proteolytic enzymes, which is now quite diverse and contains more than 25 different variants [4–6], but for which only very few members from invertebrates have been characterized until now.…”