PBP5_C

Penicillin-binding protein 5, C-terminal domain
PBP5_C
SMART accession number:SM00936
Description: Penicillin-binding protein 5 expressed by E. coli (P04287) 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 (PF00768) is the catalytic domain. The C-terminal domain featured in this family is organised into a sandwich of two anti-parallel beta-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).
Interpro abstract (IPR012907):

In the MEROPS database peptidases and peptidase homologues are grouped into clans and families. Clans are groups of families for which there is evidence of common ancestry based on a common structural fold:

  • Each clan is identified with two letters, the first representing the catalytic type of the families included in the clan (with the letter 'P' being used for a clan containing families of more than one of the catalytic types serine, threonine and cysteine). Some families cannot yet be assigned to clans, and when a formal assignment is required, such a family is described as belonging to clan A-, C-, M-, N-, S-, T- or U-, according to the catalytic type. Some clans are divided into subclans because there is evidence of a very ancient divergence within the clan, for example MA(E), the gluzincins, and MA(M), the metzincins.
  • Peptidase families are grouped by their catalytic type, the first character representing the catalytic type: A, aspartic; C, cysteine; G, glutamic acid; M, metallo; N, asparagine; S, serine; T, threonine; and U, unknown. The serine, threonine and cysteine peptidases utilise the amino acid as a nucleophile and form an acyl intermediate - these peptidases can also readily act as transferases. In the case of aspartic, glutamic and metallopeptidases, the nucleophile is an activated water molecule. In the case of the asparagine endopeptidases, the nucleophile is asparagine and all are self-processing endopeptidases.

In many instances the structural protein fold that characterises the clan or family may have lost its catalytic activity, yet retain its function in protein recognition and binding.

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 beta-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)].

GO process:proteolysis (GO:0006508)
GO function:serine-type D-Ala-D-Ala carboxypeptidase activity (GO:0009002)
Family alignment:
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There are 4641 PBP5_C domains in 4641 proteins in SMART's nrdb database.

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