Proteolytic enzymes that exploit serine in their catalytic activity are ubiquitous, being found in viruses, bacteria and eukaryotes [ PUBMED:7845208 ]. They include a wide range of peptidase activity, including exopeptidase, endopeptidase, oligopeptidase and omega-peptidase activity. Many families of serine protease have … expand

Proteolytic enzymes that exploit serine in their catalytic activity are ubiquitous, being found in viruses, bacteria and eukaryotes [ PUBMED: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 [ PUBMED: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 [ PUBMED: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 [ PUBMED:7845208 ]. The geometric orientations of the catalytic residues are similar between families, despite different protein folds [ PUBMED: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) [ PUBMED:7845208 PUBMED:8439290 ].

This entry contains proteins that are annotated as penicillin-binding protein 5 and 6. These belong to MEROPS peptidase family S11 (D-Ala-D-Ala carboxypeptidase A family, clan SE). Penicillin-binding protein 5 expressed by Escherichia coli functions as a D-alanyl-D-alanine carboxypeptidase. It is composed of two domains that are oriented at approximately right angles to each other. The N-terminal domain ( IPR001967 ) is the catalytic domain. The C-terminal domain, this entry, is organised into a sandwich of two anti-parallel β-sheets, and has a relatively hydrophobic surface as compared to the N-terminal domain. Its precise function is unknown; it may mediate interactions with other cell wall-synthesising enzymes, thus allowing the protein to be recruited to areas of active cell wall synthesis. It may also function as a linker domain that positions the active site in the catalytic domain closer to the peptidoglycan layer, to allow it to interact with cell wall peptides [ PUBMED:10967102 ].