AB5 toxin

The AB5 (or AB5) toxins are six-component protein complexes secreted by a number of pathogenic bacteria. All share a similar structure and mechanism for entering targeted host cells.

Structure and mechanism
A complete AB5 toxin complex contains six protein units. Five – the B subunits – are similar or identical in structure; the remaining A subunit is unique.

The A subunit (or a portion thereof) of an AB5 toxin is the portion of the complex responsible for toxicity. Typically it will have enzymatic activity inside the host cell.

The B subunits form a pentameric (five-membered) ring, into which one end of the A subunit extends and is held. This B subunit ring is also capable of binding to a receptor on the surface of the host cell. (Without the B subunits, the A subunit has no way of attaching to or entering the cell, and thus no way to exert its toxic effect.)

List of AB5 toxins

 * Campylobacter jejuni enterotoxin (from Campylobacter jejuni)
 * cholera toxin (Vibrio cholerae)
 * heat-labile enterotoxins (LT and LT-II) (Escherichia coli)
 * pertussis toxin (Bordetella pertussis)
 * shiga toxin (Shigella dysenteriae)
 * shiga-like toxin (or verotoxin) (enterohemorrhagic varieties of E. coli including O157:H7)