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From Wikipedia, the free encyclopedia

Cholera toxin, an AB5 toxin. the A subunit is red and orange; the B subunit is blue. A portion of the B subunit complex has been rendered partially transparent to show the bound tail of the A2 chain.

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.[1]

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.[2] (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


  1. ^ Merritt E, Hol W (1995). "AB5 toxins". Curr Opin Struct Biol 5 (2): 165–71. doi:10.1016/0959-440X(95)80071-9. PMID 7648317.  
  2. ^ Lencer W, Saslowsky D (2005). "Raft trafficking of AB5 subunit bacterial toxins". Biochim Biophys Acta 1746 (3): 314–21. doi:10.1016/j.bbamcr.2005.07.007. PMID 16153723.  


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