AB toxin

ADPrib_exo_Tox
File:PDB 1giq EBI.jpg crystal structure of the enzymatic component of iota-toxin from clostridium perfringens with nadh
Identifiers
Symbol	ADPrib_exo_Tox
Pfam	PF03496
Pfam clan	CL0084
InterPro	IPR003540
SCOP	1giq
SUPERFAMILY	1giq
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Binary_toxB
File:PDB 1tzo EBI.jpg crystal structure of the anthrax toxin protective antigen heptameric prepore
Identifiers
Symbol	Binary_toxB
Pfam	PF03495
InterPro	IPR003896
SCOP	1acc
SUPERFAMILY	1acc
TCDB	1.C.42
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

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. 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. The "A" subunit possesses enzyme activity, and is transferred to the host cell following a conformational change in the membrane-bound transport "B" subunit. 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.

Members of the "A" binary toxin family include C. perfringens iota toxin Ia, C. botulinum C2 toxin CI, and Clostridium difficile ADP-ribosyltransferase . Other homologous proteins have been found in Clostridium spiroforme.

Members of the "B" binary toxin family include the Bacillus anthracis protective antigen (PA) protein, The toxin comprises three 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 and LF) into target cells. PA protein forms the central part of the complete anthrax toxin, and translocates the B moiety into host cells after assembling as a heptamer in the membrane.

The Diphteria 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.

References

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

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