Peptidase S55, sporulation stage IV, protein B (IPR014219)

Short name: Pept_S55_SpoIVB

Overlapping homologous superfamilies


Family relationships



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].

SpoIVB, the stage IV sporulation protein B of endospore-forming bacteria such as Bacillus subtilis, is a serine proteinase expressed in the spore (rather than mother cell) compartment, that participates in a proteolytic activation cascade for Sigma-K. It appears to be universal among endospore-forming bacteria and occurs nowhere else. The members of this entry belong to MEROPS peptidase family S55 (SpoIVB peptidase, clan PA).

Contributing signatures

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