Peptidase S51, cyanophycinase (IPR011811)

Short name: Peptidase_S51_cyanophycinase

Overlapping homologous superfamilies

Family relationships

  • Peptidase S51 (IPR005320)
    • Peptidase S51, cyanophycinase (IPR011811)


Proteolytic enzymes that exploit serine in their catalytic activity are ubiquitous, being found in viruses, bacteria and eukaryotes [PMID: 7845208]. 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 [PMID: 7845208]. 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 [PMID: 7845208].

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 [PMID: 7845208]. The geometric orientations of the catalytic residues are similar between families, despite different protein folds [PMID: 7845208]. 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) [PMID: 7845208, PMID: 8439290].

This entry describes both cytosolic and extracellular cyanophycinases. These are serine exopeptidases that hydrolyse alpha-aspartyl bonds and belonging to MEROPS peptidase family S51, clan PC. They are part of a system in many Cyanobacteria and a few other species of generating and later utilizing a storage polymer for nitrogen, carbon, and energy, called cyanophycin. The latter are found in species such as Pseudomonas anguilliseptica that can use external cyanophycin. The polymer has a backbone of L-aspartic acid, with most Asp side chain carboxyl groups attached to L-arginine.

GO terms

Biological Process

GO:0044260 cellular macromolecule metabolic process

Molecular Function

GO:0016787 hydrolase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.