|Family type peptidase||M97.001 - EcxAB peptidase (Escherichia coli), MEROPS Accession MER0494979 (peptidase unit: 21-285)|
|Content of family|
Identifier created: MEROPS 9.10 (20 December 2013)|
The AB5 toxins are key virulence factors from pathogenic bacteria such as Vibrio cholerae. Each toxin is a heterooligomer consisting of an enzymatic A subunit and five B subunits. The B subunits are required for cell invasion and bind to cell surface glycans, whereupon the enzymatic subunit A, known as the 'cargo', is internalized by the host cell, activates and disrupts cellular function (Ng et al., 2013). The A subunit is frequently an ADP-ribosyltransferase or an RNA-glycosidase, but in some toxins may be a peptidase, such as the subtilisin homologue in the subtilase cytotoxin (S08.121; Paton et al., 2004). In the EcxAB toxin from Echerichia coli, the enzymatic A subunit is a Met-zincin-like metallopeptidase with an HEXXHXXGXXH zinc-binding motif (Ng et al., 2013).
|Active site residues||E180 |
|Active site||From the tertiary structure, the active site residues is the glutamic acid and the zinc ligands are the histidines within the HEXXHXXGXXH motif found in subunit A. The Met-turn is present but is preceded by a loop that interacts with the B subunits (Ng et al., 2013).|
|Activities and specificities||No peptidolytic activity has so far been demonstrated, and it has been proposed that the crystallized form, which is a heterooligomer, may represent a latent form of the peptidase, which once released from its carrier B subunits becomes active following a probable structural rearrangement (Ng et al., 2013).|
|Molecular structure||The structure of the EcxAB peptidase has been solved and shows a fold similar to that of other Met-zincins Ng et al., 2013). Consequently, family M97 in included in clan MA, subclan MA(M).|