Peptidase S49, protease IV (IPR004634)

Short name: Pept_S49_pIV

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].

This group of serine peptidases belong to MEROPS peptidase family S49 (protease IV family, clan S-). The predicted active site serine for members of this family occurs in a transmembrane domain.

Signal peptides of secretory proteins seem to serve at least two important biological functions. First, they are required for protein targeting to and translocation across membranes, such as the eubacterial plasma membrane and the endoplasmic reticular membrane of eukaryotes. Second, in addition to their role as determinants for protein targeting and translocation, certain signal peptides have a signalling function.

During or shortly after pre-protein translocation, the signal peptide is removed by signal peptidases. The integral membrane protein, SppA (protease IV), of Escherichia coli was shown experimentally to degrade signal peptides. The member of this family from Bacillus subtilis has only been shown to be required for efficient processing of pre-proteins under conditions of hyper-secretion [PMID: 10455123]. These enzymes have a molecular mass around 67 kDa and a duplication such that the N-terminal half shares extensive homology with the C-terminal half and was shown in E. coli to form homotetramers. E. coli SohB, which is most closely homologous to the C-terminal duplication of SppA, is predicted to perform a similar function of small peptide degradation, but in the periplasm. Many prokaryotes have a single SppA/SohB homologue that may perform the function of either or both.

GO terms

Biological Process

GO:0006465 signal peptide processing

Molecular Function

GO:0008233 peptidase activity

Cellular Component

GO:0016021 integral component of membrane

Contributing signatures

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