Metallopeptidase

Peptidases have been classified by the MEROPS system since 1993 [2], which has been available viatheMEROPS database since 1996 [3]. The classification is based on sequence and structural similarities. Because peptidases are often multidomain proteins, only the domain directly involved in catalysis, and which beais the active site residues, is used in comparisons. This domain is known as the peptidase unit. Peptidases with statistically significant peptidase unit sequence similarities are included in the same family. To date 186 families of peptidase have been detected. Examples from 86 of these families are known in humans. A family is named from a letter representing the catalytic type ( A for aspartic, G for glutamic, M for metallo, C for cysteine, S for serine and T for threonine) plus a number. Examples of family names are shown in Table 1. There are 53 families of metallopeptidases (24 in human), 14 of aspartic peptidases (three of which are found in human), 62 of cysteine peptidases (19 in human), 42 of serine peptidases (17 in human), four of threonine peptidases (three in human), one of ghitamicpeptidases and nine families for which the catalytic type is unknown (one in human). It should be noted that within a family not all of the members will be peptidases. Usually non-peptidase homologues are a minority and can be easily detected because not all of the active site residues are conserved. 

MA M10 M10.001 Matrix metallopeptidase-1 Drug target for prevention of pathological tissue damage... 

It is recommended that a well-characterized peptidase should have a trivial name. Although not rigidly adhered to, there is a different suffix for each catalytic type, metallopeptidases names end with lysin , aspartic peptidases with pepsin , cysteine pqrtidase with ain and serine peptidases with in . 

The previous chapter offered a broad overview of peptidases and esterases in terms of their classification, localization, and some physiological roles. Mention was made of the classification of hydrolases based on a characteristic functionality in their catalytic site, namely serine hydrolases, cysteine hydrolases, aspartic hydrolases, and metallopeptidases. What was left for the present chapter, however, is a detailed presentation of their catalytic site and mechanisms. As such, this chapter serves as a logical link between the preceding overview and the following chapters, whose focus is on metabolic reactions. 

Like aspartic peptidases, metallopeptidases act by activating a H20 molecule, and they do not form a covalent intermediate with the substrate. Here, the activation of a H20 molecule is mediated by a residue that acts as general base (e.g., Glu, His, Lys, Arg, or Tyr), with a divalent cation (usually Zn2+ but sometimes Co2+ or Mn2+) perhaps also contributing. The major role of the metal cation, however, is to act as an electrophilic catalyst by coordinating the carbonyl (or phosphoryl) O-atom in the substrate and orienting the latter for nucleophilic attack by the HO ion generated from H20 by the general base. 

The metal ion is held in place by amino acid residues, generally His, Glu, Asp, or Lys. In many metallopeptidases, which may be exopeptidases or en-dopeptidases, only one zinc ion is required. In all Co2+ or Mn2+-dependent, and in some Zn2+-dependent metallopeptidases, two metal ions are present and act cocatalytically these enzymes are exopeptidases [2][73][74],... 

Neprilysin (enkephalinase, Endopeptidase-24.11, neutral endopeptidase, NEP, EC 3.4.24.11) bears considerable resemblance to other zinc-containing metallopeptidases it is an oligopeptidase that hydrolyzes enkephalins and a range of other active peptides. Enkephalins are endogenous ligands of opiate receptors, and the prolongation of their action via inhibition of enkephalinase... 

Metallopeptidases display an equal or greater catalytic efficiency toward peptides than toward the corresponding esters [84], This behavior is the opposite of that observed with serine peptidases and is unexpected, since the ester bond is chemically more labile than an amide bond. It has been postulated that the difference in catalytic efficiency is due to difference in product release, meaning that this step could be rate-limiting for esters but not for amides [85]. 

In the other subdivision, water activation occurs in the first step of the enzymatic cycle. This activation is achieved by a carboxylate group in aspartic hydrolases (Fig. 3.10), Zn2+ and a carboxy group in metallopep-tidases (Fig. 3.12 ), a histidine side chain in calcium-dependent hydrolases (Fig. 3.14), or a Zn2+ in carbonic anhydrase (Fig. 3.15). The substrate, on the other hand, is polarized (activated) by a carboxy group in aspartic hydrolases or by a cation in metallopeptidases and calcium-dependent hydrolases. In this manner, the reactivity of both the water molecule and the substrate is enhanced and fine-tuned to drive formation of a tetrahedral intermediate that will break down to form the hydrolysis products. 

A metallopeptidase isolated from hemolytic streptococci. It hydrolyzes peptide bonds in plasminogen, producing plasmin. 

Rawlings ND, Barrett AJ (1995) Evolutionary families of metallopeptidases. Methods En-zymol 248 183-228... 

After translocation into the mitosome, the N-terminal presequences of mitosomal proteins are cleaved off, most likely by a peptidase that is homologous to the mitochondrial processing peptidase (MPP). The MPP is a matrix-localized metallopeptidase with a zinc binding motif His-X-X-Glu-His that is conserved in the putative mitosomal processing peptidase reported in G. intestinalis (Dolezal et al. 2005). 

Membranes, for electroblots, 185-198 Metallopeptidases, 365 Methanol, in protein electroblots, 185-198 Methionine digestibility of, 135 hydrolysis, effect on, 134 Methylation... 

The above studies indicate that metal ions catalyze the hydrolysis of amides and peptides at pH values where the carbonyl-bonded species (25) is present. At higher pH values where deprotonated complexes (26) can be formed the hydrolysis is inhibited. These conclusions have been amply confirmed in subsequent studies involving inert cobalt(III) complexes (Section 61.4.2.2.2). Zinc(II)-promoted amide ionization is uncommon, and the first example of such a reaction was only reported in 1981.103 Zinc(II) does not inhibit the hydrolysis of glycylglycine at high pH, and amide deprotonation does not appear to occur at quite high pH values. Presumably this is one important reason for the widespread occurrence of zinc(Il) in metallopeptidases. Other metal ions such as copper(II) would induce amide deprotonation at relatively low pH values leading to catalytically inactive complexes. 

The active sites of ACE contain the sequence His-Glu-X-X-His, in which the histidines are considered to participate in Zn2+ binding and Glu in the catalytic mechanism. A third Zn2+ ligand is proposed to be a glutamic acid, and the fourth is the nucleophilic water molecule (62). This structural motif is present in a number of metallopeptidases,... 

Owing to the complementary roles of NEP and APN in enkephalin inactivation, selective inhibitor of only one of the two peptidases gives weak antinoceptive effects even after ICV administration. This led us to propose the concept of mixed inhibitors, that is, compounds able to simultaneously block NEP and APN activities [reviews in 9,20]. This was possible owing to the fact that these two membrane-bound enzymes belong to the superfamily of zinc metallopeptidases. 

Bravo-Osuna, I., C. Vauthier, et al. (2008). Effect of chitosan and thiolated chitosan coating on the inhibition behaviour of PIBCA nanoparticles against intestinal metallopeptidases. J. Nanopart. Res DOI 10.1007/sl 1051-008-9364-5. 

A variety of plant bioactives inhibit the metallopeptidase aminopeptidase N [63-68], the most potent inhibitors (variously active at 1-7 pM) being the phenolics curcumin, phloretin and quercetin [64-67] and the lupane triterpene betulinic acid (IC5o value 7 pM) [68] (Table 2). 

Table 2. Plant non-protein metallopeptidase inhibitors For details see the legend to Table 1.

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