SMART accession number:SM00631
Description: -
Interpro abstract (IPR000834):

Metalloproteases are the most diverse of the four main types of protease, with more than 50 families identified to date. In these enzymes, a divalent cation, usually zinc, activates the water molecule. The metal ion is held in place by amino acid ligands, usually three in number. The known metal ligands are His, Glu, Asp or Lys and at least one other residue is required for catalysis, which may play an electrophillic role. Of the known metalloproteases, around half contain an HEXXH motif, which has been shown in crystallographic studies to form part of the metal-binding site [(PUBMED:7674922)]. The HEXXH motif is relatively common, but can be more stringently defined for metalloproteases as 'abXHEbbHbc', where 'a' is most often valine or threonine and forms part of the S1' subsite in thermolysin and neprilysin, 'b' is an uncharged residue, and 'c' a hydrophobic residue. Proline is never found in this site, possibly because it would break the helical structure adopted by this motif in metalloproteases [(PUBMED:7674922)].

This group of sequences contain a diverse range of gene families, which include metallopeptidases belonging to MEROPS peptidase family M14 (carboxypeptidase A, clan MC), subfamilies M14A and M14B.

The carboxypeptidase A family can be divided into two subfamilies: carboxypeptidase H (regulatory) and carboxypeptidase A (digestive) [(PUBMED:7674922)]. Members of the H family have longer C-termini than those of family A [(PUBMED: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 [(PUBMED: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 [(PUBMED:7674922), (PUBMED: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 [(PUBMED:7674922), (PUBMED:1548696)].

Other examples of protein families in this entry include:

  • Intron maturase
  • Putative mitochondrial processing peptidase alpha subunit
  • Superoxide dismutase [Mn] (EC
  • Asparagine synthetase [glutamine-hydrolysing] 3 (EC
  • Glucose-6-phosphate isomerase (EC

GO process:proteolysis (GO:0006508)
GO function:metallocarboxypeptidase activity (GO:0004181), zinc ion binding (GO:0008270)
Family alignment:
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There are 6332 Zn_pept domains in 6039 proteins in SMART's nrdb database.

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