Family

Peptidase M48, protease HtpX, putative (IPR022919)

Short name: Pept_M48_protease_HtpX

Family relationships

  • Peptidase M48 (IPR001915)
    • Peptidase M48, protease HtpX, putative (IPR022919)

Description

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.

Metalloproteases are the most diverse of the four main types of protease, with more than 50 families identified to date. In these enzymes, a divalent cation, usually zinc, activates the water molecule. The metal ion is held in place by amino acid ligands, usually three in number. The known metal ligands are His, Glu, Asp or Lys and at least one other residue is required for catalysis, which may play an electrophillic role. Of the known metalloproteases, around half contain an HEXXH motif, which has been shown in crystallographic studies to form part of the metal-binding site [PMID: 7674922]. The HEXXH motif is relatively common, but can be more stringently defined for metalloproteases as 'abXHEbbHbc', where 'a' is most often valine or threonine and forms part of the S1' subsite in thermolysin and neprilysin, 'b' is an uncharged residue, and 'c' a hydrophobic residue. Proline is never found in this site, possibly because it would break the helical structure adopted by this motif in metalloproteases [PMID: 7674922].

This group of metallopeptidases belong to MEROPS peptidase family M48 (subfamily M48B). The members of this set of proteins are mostly described as probable protease htpX homologue (EC:3.4.24).

HtpX is a zinc-dependent endoprotease member of the membrane-localized proteolytic system in E. coli, which participates in the proteolytic quality control of membrane proteins in conjunction with FtsH, a membrane-bound and ATP-dependent protease. Biochemical characterisation revealed that HtpX undergoes self-degradation upon cell disruption or membrane solubilisation. It can also degraded casein and cleaves solubilised membrane proteins, for example, SecY [PMID: 16076848]. Expression of HtpX in the plasma membrane is under the control of CpxR, with the metalloproteinase active site of HtpX located on the cytosolic side of the membrane. This suggests a potential role for HtpX in the response to mis-folded proteins [PMID: 12081643].

GO terms

Biological Process

No terms assigned in this category.

Molecular Function

GO:0004222 metalloendopeptidase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

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