InterPro domain: IPR001818

Over 70 metallopeptidase families have been identified to date. In these enzymes a divalent cation which is usually zinc, but may be cobalt, manganese or copper, activates the water molecule. The metal ion is held in place by amino acid ligands, usually three in number. In some families of co-catalytic metallopeptidases, two metal ions are observed in crystal structures ligated by five amino acids, with one amino acid ligating both metal ions. The known metal ligands are His, Glu, Asp or Lys. At least one other residue is required for catalysis, which may play an electrophillic role. Many metalloproteases contain an HEXXH motif, which has been shown in crystallographic studies to form part of the metal-binding site [ 1 ]. 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 [ 2 ].

This group of metallopeptidases belong to the MEROPS peptidase family M10 (clan MA(M)).

The protein fold of the peptidase domain for members of this family resembles that of thermolysin, the type example for clan MA.

Sequences having this domain are extracellular metalloproteases, such as collagenase and stromelysin, whichdegrade the extracellular matrix, are known as matrixins. They are zinc-dependent,calcium-activated proteases synthesised as inactive precursors(zymogens), which are proteolytically cleaved to yield the active enzyme[ 2 , 3 ]. All matrixins and related proteins possess 2 domains: an N-terminaldomain, and a zinc-binding active site domain. The N-terminal domainpeptide, cleaved during the activation step, includes a conserved PRCGVPDVoctapeptide, known as the cysteine switch, whose Cys residue chelates theactive site zinc atom, rendering the enzyme inactive [ 4 , 5 ]. The active enzymedegrades components of the extracellular matrix, playing a role in theinitial steps of tissue remodelling during morphogenesis, wound healing,angiogenesis and tumour invasion [ 6 , 6 ].

1. Evolutionary families of metallopeptidases. Meth. Enzymol. 248, 183-228
2. SV40-transformed human lung fibroblasts secrete a 92-kDa type IV collagenase which is identical to that secreted by normal human macrophages. J. Biol. Chem. 264, 17213-21
3. Early expression of a collagenase-like hatching enzyme gene in the sea urchin embryo. EMBO J. 9, 3003-12
4. Structure-function relationships in the collagenase family member transin. J. Biol. Chem. 263, 11892-9
5. Mutational analysis of the transin (rat stromelysin) autoinhibitor region demonstrates a role for residues surrounding the "cysteine switch". J. Biol. Chem. 266, 1584-90