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123  structures 365  species 4  interactions 469  sequences 37  architectures

Family: ADPrib_exo_Tox (PF03496)

Summary: ADP-ribosyltransferase exoenzyme

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This is the Wikipedia entry entitled "AB toxin". More...

AB toxin Edit Wikipedia article

PDB 1giq EBI.jpg
crystal structure of the enzymatic component of iota-toxin from clostridium perfringens with nadh
Symbol ADPrib_exo_Tox
Pfam PF03496
Pfam clan CL0084
InterPro IPR003540
SCOP 1giq
PDB 1tzo EBI.jpg
crystal structure of the anthrax toxin protective antigen heptameric prepore
Symbol Binary_toxB
Pfam PF03495
InterPro IPR003896
SCOP 1acc
TCDB 1.C.42

The AB toxins are two-component protein complexes secreted by a number of pathogenic bacteria. They can be classified as Type III toxins because they interfere with internal cell function.[1] They are named AB toxins due to their components: the "A" component is usually the "active" portion, and the "B" component is usually the "binding" portion.[1][2] The "A" subunit possesses enzyme activity, and is transferred to the host cell following a conformational change in the membrane-bound transport "B" subunit.[3] Among the toxins produced by certain Clostridium spp. are the binary exotoxins. These proteins consist of two independent polypeptides, which correspond to the A/B subunit moieties. The enzyme component (A) enters the cell through endosomes produced by the oligomeric binding/translocation protein (B), and prevents actin polymerisation through ADP-ribosylation of monomeric G-actin.[3][4][5]

Examples of the "A" component of an AB toxin include C. perfringens iota toxin Ia,[3] C. botulinum C2 toxin CI,[4] and Clostridium difficile ADP-ribosyltransferase .[5] Other homologous proteins have been found in Clostridium spiroforme.[4][5]

An example of the B component of an AB toxin is Bacillus anthracis protective antigen (PA) protein,[3] B. anthracis secretes three toxin factors: the protective antigen (PA); the oedema factor (EF); and the lethal factor (LF). Each is a thermolabile protein of ~80kDa. PA forms the "B" part of the exotoxin and allows passage of the "A" moiety (consisting of EF or LF) into target cells. PA protein forms the central part of the complete anthrax toxin, and translocates the A moiety into host cells after assembling as a heptamer in the membrane.[6][7]

The Diphtheria toxin also is an AB toxin. It inhibits protein synthesis in the host cell through phosphorylation of the eukaryotic elongation factor 2, which is an essential component for protein synthesis. The exotoxin A of Pseudomonas aeruginosa is another example of an AB toxin that targets the eukaryotic elongation factor 2.

The AB5 toxins are usually considered a type of AB toxin, characterized by B pentamers. Less commonly, the term "AB toxin" is used to emphasize the monomeric character of the B component.


  1. ^ a b "Bacterial Pathogenesis: Bacterial Factors that Damage the Host - Producing Exotoxins - A-B Toxins". Archived from the original on 2010-07-27. Retrieved 2008-12-13. 
  2. ^ De Haan L, Hirst TR (2004). "Cholera toxin: a paradigm for multi-functional engagement of cellular mechanisms (Review)". Mol. Membr. Biol. 21 (2): 77–92. doi:10.1080/09687680410001663267. PMID 15204437. 
  3. ^ a b c d Perelle S, Gibert M, Boquet P, Popoff MR (December 1993). "Characterization of Clostridium perfringens iota-toxin genes and expression in Escherichia coli". Infect. Immun. 61 (12): 5147–56. PMC 281295Freely accessible. PMID 8225592. 
  4. ^ a b c Fujii N, Kubota T, Shirakawa S, Kimura K, Ohishi I, Moriishi K, Isogai E, Isogai H (March 1996). "Characterization of component-I gene of botulinum C2 toxin and PCR detection of its gene in clostridial species". Biochem. Biophys. Res. Commun. 220 (2): 353–9. doi:10.1006/bbrc.1996.0409. PMID 8645309. 
  5. ^ a b c Stubbs S, Rupnik M, Gibert M, Brazier J, Duerden B, Popoff M (May 2000). "Production of actin-specific ADP-ribosyltransferase (binary toxin) by strains of Clostridium difficile". FEMS Microbiol. Lett. 186 (2): 307–12. doi:10.1111/j.1574-6968.2000.tb09122.x. PMID 10802189. 
  6. ^ Pezard C, Berche P, Mock M (October 1991). "Contribution of individual toxin components to virulence of Bacillus anthracis". Infect. Immun. 59 (10): 3472–7. PMC 258908Freely accessible. PMID 1910002. 
  7. ^ Welkos SL, Lowe JR, Eden-McCutchan F, Vodkin M, Leppla SH, Schmidt JJ (September 1988). "Sequence and analysis of the DNA encoding protective antigen of Bacillus anthracis". Gene. 69 (2): 287–300. doi:10.1016/0378-1119(88)90439-8. PMID 3148491. 

This article incorporates text from the public domain Pfam and InterPro IPR003540

This article incorporates text from the public domain Pfam and InterPro IPR003896

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

ADP-ribosyltransferase exoenzyme Provide feedback

This is a family of bacterial and viral bi-glutamic acid ADP-ribosyltransferases, where, in Q93Q17 E403 is the catalytic residue and E401 contributes to the transfer of ADP-ribose to the target protein. In clostridial species it is actin that is being ADP-ribosylated; this result is lethal and dermonecrotic in infected mammals.

Literature references

  1. Radke J, Pederson KJ, Barbieri JT;, Infect Immun. 1999;67:1508-1510.: Pseudomonas aeruginosa exoenzyme S is a biglutamic acid ADP-ribosyltransferase. PUBMED:10024602 EPMC:10024602

  2. Tsuge H, Nagahama M, Nishimura H, Hisatsune J, Sakaguchi Y, Itogawa Y, Katunuma N, Sakurai J;, J Mol Biol. 2003;325:471-483.: Crystal structure and site-directed mutagenesis of enzymatic components from Clostridium perfringens iota-toxin. PUBMED:12498797 EPMC:12498797

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR003540

ADP-ribosylation is a posttranslational modification of proteins involving the addition of one or more ADP-ribose moieties [PUBMED:17161604, PUBMED:10712584]. These reactions are involved in cell signaling and the control of many cell processes, including DNA repair and apoptosis [PUBMED:15003268, PUBMED:12727863].

This entry represents an ADP-ribosyltransferase domain found in various proteins, including bacterial and viral toxins.

Gene Ontology

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Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan ADP-ribosyl (CL0084), which has the following description:

The members of this clan all represent ADP-ribosylating catalytic domains. The structurally conserved regions are located at the NAD binding region [1]. According to SCOP, the ADP-ribosylation domain is thought to have an "unusual fold".

The clan contains the following 19 members:

ADPrib_exo_Tox ADPRTs_Tse2 Anthrax-tox_M Arr-ms ART ART-PolyVal AvrPphF-ORF-2 Diphtheria_C Dot_icm_IcmQ DUF2441 DUF952 Enterotoxin_a Exotox-A_cataly NADase_NGA PARP Pertussis_S1 PTS_2-RNA RolB_RolC TNT


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Curation and family details

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Seed source: PRINTS
Previous IDs: Binary_toxA;
Type: Family
Sequence Ontology: SO:0100021
Author: Griffiths-Jones SR
Number in seed: 22
Number in full: 469
Average length of the domain: 178.70 aa
Average identity of full alignment: 17 %
Average coverage of the sequence by the domain: 27.90 %

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HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 45638612 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 23.4 21.9
Trusted cut-off 23.4 21.9
Noise cut-off 23.3 21.8
Model length: 197
Family (HMM) version: 14
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Species distribution

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Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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There are 4 interactions for this family. More...

ATLF Ras Actin ADPrib_exo_Tox


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the ADPrib_exo_Tox domain has been found. There are 123 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.

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