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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.
A third protein can sometimes be involved in type II toxin-antitoxin systems. in the case of the ω-ε-ζ (omega-epsilon-zeta) system, the omega protein is a DNA binding protein that negatively regulates the transcription of the whole system. [64] Similarly, the paaR2 protein regulates the expression of the paaR2-paaA2-parE2 toxin-antitoxin ...
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.
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.
Pore-forming proteins (PFTs, also known as pore-forming toxins) are usually produced by bacteria, and include a number of protein exotoxins but may also be produced by other organisms such as apple snails that produce perivitellin-2 [1] [2] or earthworms, who produce lysenin.
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.
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 ...
In the nucleotide sequence of TSST-1, there is a 708 base-pair open-reading frame and a Shine-Dalgarno sequence which is seven base pairs downstream from the start site. [6] In the entire nucleotide sequence, only 40 amino acids make up the signal peptide.