This family consists of probable oligoendopeptidases belonging to MEROPS peptidase family M3, subfamily M3B (clan MA(E)). The family is related to lactococcal PepF and group B streptococcal PepB () but in a distinct clade with considerable sequence differences not only to but also to . Likely substrates are small peptides and not whole proteins, as with PepF, but members are not characterised and the activity profile may differ. Several bacteria have both a member of this family and a member of the PepF family.
Oligopeptidase F (PepF; Pz-peptidase B; MEROPS identifier M03.010) is mostly bacterial and includes oligoendopeptidase F from Lactococcus lactis. This enzyme hydrolyzes peptides containing between 7 and 17 amino acids with fairly broad specificity. The PepF gene is duplicated in L. lactis on the plasmid that bears it, while a shortened second copy is found in Bacillus subtilis. Most bacterial PepFs are cytoplasmic endopeptidases; however, the PepF Bacillus amyloliquefaciens oligopeptidase is a secreted protein and may facilitate the process of sporulation []. Specifically, the yjbG gene encoding the homologue of the PepF1 and PepF2 oligoendopeptidases of Lactococcus lactis has been identified in Bacillus subtilis as an inhibitor of sporulation initiation when over expressed from a multicopy plasmid [].
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 []. 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 family consists of probable oligoendopeptidases belonging to MEROPS peptidase family M3, subfamily M3B (clan MA(E)). It is related to lactococcal PepF and group B streptococcal PepB () but in a distinct clade with considerable sequence differences not only to but also to . Members are not characterised with respect to their substrates and the activity profile may differ.
