Family M97


Summary Holotypes Alignment Tree Genomes Structure Literature

Summary for family M97

Family type peptidaseM97.001 - EcxAB peptidase (Escherichia coli), MEROPS Accession MER0494979 (peptidase unit: 21-285)
Content of family
History 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).
Catalytic typeMetallo
Active site residuesH179 E180 H183 H189 
Active siteFrom 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 specificitiesNo 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 structureThe 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).
Distribution of family Bacteria details  
Archaea -  
Protozoa -  
Fungi -  
Plants -  
Animals -  
Viruses -  
Biological functions
Statistics for family M97Sequences:170
Identifiers with PDB entries:1
Downloadable files Sequence library (FastA format)
Sequence alignment (FastA format)
Phylogenetic tree (Newick format)
Peptidases and Homologues MEROPS ID Structure
EcxAB peptidaseM97.001Yes
non-peptidase homologue-
family M97 unassigned peptidasesunassigned-