| Type: | Family | Name: | Peptidase M20A, peptidase V |
| Description: | 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 []. 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 [].This entry represents a small clade of dipeptidase enzymes from the Lactobacillaceae, which belong to MEROPS peptidase family M20A. The Lactococcus lactisenzyme has been shown to act on a wide range of dipeptides, but not larger peptides. The enzyme from Lactobacillus delbrueckiiwas originally characterised as a Xaa-His dipeptidase, specifically a carnosinase (beta-Ala-His) by complementation of an Escherichia colimutant. Further study, including the crystallisation of the enzyme [], has shown it to also be a non-specific dipeptidase. This group also includes enzymes from Streptococcus and Enterococcus. | Short Name: | Pept_M20A_peptidaseV |
