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Main articles: and This family is also known as SubAB and was discovered during the 1990s. It produced by strains of STEC that do not have the (LEE), and is known to cause hemolytic-uremic syndrome (HUS). It is called a subtilase cytotoxin because its A subunit sequence is similar to that of a subtilase-like in. Some symptoms caused by this toxin are a decrease in count in the blood or, an increase in count or, and cell damage.

Structure [ ] A complete AB5 toxin complex contains six protein units. Five units are similar or identical in structure and they comprise the B subunit. The last protein unit is unique and is known as the A subunit. Ribbon diagram of the B-subunit of the cholera toxin. A subunit [ ] The A subunit of an AB5 toxin is the portion responsible for catalysis of specific targets. For Shiga toxin family, the A subunit hosts a -sensitive region which gives out two fragmented domains when cleaved.

This region has not been confirmed for the other AB5 toxin families as yet. In general, the two domains of the A subunit, named A1 and A2, are linked by a. Domain A1 (approximately 22kDa in cholera toxin or heat labile enterotoxins) is the part of the toxin responsible for its toxic effects. Domain A2 (approximately 5kDa in cholera toxin or heat labile enterotoxin) provides a linkage to the B subunit through the B subunit's central pore.

The A1 chain for cholera toxin catalyzes the transfer of from (NAD) to or other compounds by utilizing (ARFs). In the absence of arginine or simple guanidino compounds, the toxin mediated (NADase) activity proceeds using water as a.

B subunit [ ] The B subunits form a five-membered or pentameric ring, where one end of the A subunit goes into and is held. This B subunit ring is also capable of binding to a 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. Cholera toxin, shiga toxin, and SubAB toxin all have B subunits that are made up of five identical protein components, meaning that their B subunits are homopentamers.

Pertussis toxin is different where its pentameric ring is made up of four different protein components, where one of the components is repeated to form a heteropentamer. Mechanisms [ ] Cholera toxin, pertussis toxin, and shiga toxin all have their targets in the of the cell.

After their B subunit binds to receptors on the cell surface, the toxin is enveloped by the cell and transported inside either through. The mechanism pathways for the four AB5 toxins: cholera toxin, pertussis toxin, shiga toxin, and subtilase cytotoxin. For the cholera toxin, the principal receptor for the cholera toxin is.

After endocytosis to the, the toxin is redirected to the. In order for the A subunit to reach its target, a disulfide bond between the A1 and A2 domain must be broken.

This breakage is catalyzed by a that is in the endoplasmic reticulum. Following separation, the A1 domain unfolds and is redirected back to the cytosol where it refolds and catalyzes of certain alpha subunits.