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Some exotoxins act directly at the ribosome to inhibit protein synthesis. An example is Shiga toxin. Other toxins act at elongation factor-2. In the case of the diphtheria toxin, EF2 is ADP-ribosylated and becomes unable to participate in protein elongation, and, so, the cell dies. Pseudomonas exotoxin has a similar action.
It is slightly unusual in that it combines the A and B parts in the same protein chain: the pre-toxin is cleaved into two parts, then the two parts are joined by a disulfide bond. [5] The exotoxin A of Pseudomonas aeruginosa is another example of an AB toxin that targets the eEF2. The "A" part is structually similar to the DT "A" part; the "B ...
The Pseudomonas exotoxin (or exotoxin A) is an exotoxin produced by Pseudomonas aeruginosa. [1] Vibrio cholerae produces a similar protein called the Cholix toxin 2] It inhibits elongation factor-2. It does so by ADP-ribosylation of EF2 using NAD+. This then causes the elongation of polypeptides to cease.
Diphtheria toxin is a single polypeptide chain of 535 amino acids consisting of two subunits linked by disulfide bridges, known as an A-B toxin.Binding to the cell surface of the B subunit (the less stable of the two subunits) allows the A subunit (the more stable part of the protein) to penetrate the host cell.
Pertussis toxin is an exotoxin with six subunits (named S1 through S5—each complex contains two copies of S4). [12] [13] The subunits are arranged in A-B structure: the A component is enzymatically active and is formed from the S1 subunit, while the B component is the receptor-binding portion and is made up of subunits S2–S5. [13]
Often the toxin and antitoxin are encoded on opposite strands of DNA. The 5' or 3' overlapping region between the two genes is the area involved in complementary base-pairing, usually with between 19–23 contiguous base pairs. [39] Toxins of type I systems are small, hydrophobic proteins that confer toxicity by damaging cell membranes. [1]
SpeB was identified in 1919 as an ectoenzyme secreted by certain strains of streptococci. [11] It was originally studied as two separate toxins, streptococcal pyrogenic exotoxin B and streptococcal cysteine proteinase, until it was shown that both proteins were encoded by the speB gene and that the attributed pyrogenic activities were due to contamination by SpeA and SpeC.
The partner proteins in these combinations may belong to different structural groups, depending on the individual toxin: two Toxin_10 proteins (BinA and BinB) act together in the Bin mosquitocidal toxin of Lysinibacillus sphaericus; [14] the Toxin_10 Cry49 is co-dependent on the 3-domain toxin family member Cry48 for its activity against Culex ...