AB5 toxin
Encyclopedia
The 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.
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.)
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
complexes secreted by a number of pathogenic
Pathogenicity
Pathogenicity is the ability of a pathogen to produce an infectious disease in an organism.It is often used interchangeably with the term "virulence", although virulence is used more specifically to describe the relative degree of damage done by a pathogen, or the degree of pathogenicity caused by...
bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. 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
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
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 jejuniCampylobacter jejuniCampylobacter jejuni is a species of curved, helical-shaped, non-spore forming, Gram-negative, microaerophilic bacteria commonly found in animal feces. It is one of the most common causes of human gastroenteritis in the world. Food poisoning caused by Campylobacter species can be severely...
) - cholera toxinCholera toxinCholera toxin is a protein complex secreted by the bacterium Vibrio cholerae. CTX is responsible for the massive, watery diarrhea characteristic of cholera infection.- Structure :...
(Vibrio choleraeVibrio choleraeVibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
) - heat-labile enterotoxins (LT and LT-II) (Escherichia coliEscherichia coliEscherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
) - pertussis toxinPertussis toxinPertussis toxin is a protein-based AB5-type exotoxin produced by the bacterium Bordetella pertussis, which causes whooping cough. PT is involved in the colonization of the respiratory tract and the establishment of infection...
(Bordetella pertussisBordetella pertussisBordetella pertussis is a Gram-negative, aerobic coccobacillus of the genus Bordetella, and the causative agent of pertussis or whooping cough. Unlike B. bronchiseptica, B. pertussis is non-motile. Its virulence factors include pertussis toxin, filamentous hæmagglutinin, pertactin, fimbria, and...
) - shiga toxinShiga toxinShiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, whose genes are considered to be part of the genome of lambdoid prophages. The toxins are named for Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. The most common...
(Shigella dysenteriaeShigella dysenteriaeShigella dysenteriae is a species of the rod-shaped bacterial genus Shigella. Shigella can cause shigellosis . Shigellae are Gram-negative, non-spore-forming, facultatively anaerobic, non-motile bacteria.S...
) - shiga-like toxinShiga-like toxinShiga-like toxin, also known as verotoxin, is a toxin generated by some strains of Escherichia coli . It is named for its similarity to the AB5-type Shiga toxin produced by the bacteria Shigella dysenteriae....
(or verotoxin) (enterohemorrhagic varieties of E. coli including O157:H7)