| Type: | Family | Name: | Peptidase S51 |
| Description: | Proteolytic enzymes that exploit serine in their catalytic activity are ubiquitous, being found in viruses, bacteria and eukaryotes []. They include a wide range of peptidase activity, including exopeptidase, endopeptidase, oligopeptidase and omega-peptidase activity. Many families of serine protease have been identified, these being grouped into clans on the basis of structural similarity and other functional evidence []. Structures are known for members of the clans and the structures indicate that some appear to be totally unrelated, suggesting different evolutionary origins for the serine peptidases [].Not withstanding their different evolutionary origins, there are similarities in the reaction mechanisms of several peptidases. Chymotrypsin, subtilisin and carboxypeptidase C have a catalytic triad of serine, aspartate and histidine in common: serine acts as a nucleophile, aspartate as an electrophile, and histidine as a base []. The geometric orientations of the catalytic residues are similar between families, despite different protein folds []. The linear arrangements of the catalytic residues commonly reflect clan relationships. For example the catalytic triad in the chymotrypsin clan (PA) is ordered HDS, but is ordered DHS in the subtilisin clan (SB) and SDH in the carboxypeptidase clan (SC) [, ].This group of serine peptidases belong to MEROPS peptidase family S51 (clan PC(S)). The type example being dipeptidase E (alpha-aspartyl dipeptidase) from Escherichia coli. The family contains alpha-aspartyl dipeptidases (dipeptidase E) and cyanophycinases.The three-dimensional structure of Salmonella typhimuriumaspartyl dipeptidase, peptidase E has been determine at 1.2-A resolution. The structure of this 25kDa enzyme consists of two mixed beta-sheets forming a V, flanked by six alpha-helices. The active site contains a Ser-His-Glu catalytic triad and is the first example of a serine peptidase/protease with a glutamate in the catalytic triad. The active site Ser is located on a strand-helix motif reminiscent of that found in alpha/beta-hydrolases, but the polypeptide fold and the organisation of the catalytic triad differ from those of the known serine proteases. This enzyme appears to represent a new example of convergent evolution of peptidase activity [].Alpha-aspartyl dipeptidase hydrolyses dipeptides containing N-terminal aspartate residues, asp-|-xaa. It does not act on peptides with N-terminal Glu, Asn or Gln, nor does it cleave isoaspartyl peptides. In the cyanobacteria, cyanophycinase is an exopeptidase that catalyses the hydrolytic cleavage of multi-l-arginyl-poly-l-aspartic acid (cyanophycin; a water- insoluble reserve polymer) into aspartate-arginine dipeptides. | Short Name: | Peptidase_S51 |
| DB identifier | UniProt Accession | Secondary Identifier | Organism Name | Length |
|---|---|---|---|---|
| 28678.m000041 | B9TBM4 | PAC:16801503 | Ricinus communis |
388
 |
| 29330.m000049 | B9TBE2 | PAC:16802652 | Ricinus communis |
227
|
