Wednesday, October 26, 2022

Pseudomonas Exotoxin A

Exotoxins are toxins, often proteins in nature, secreted from a living bacterium but also released upon bacterial lysis.

There are three main types of exotoxins:
“Superantigens (Type I toxins);
“Exotoxins that damage host cell membranes (Type II toxins);
*A-B toxins and other toxin that interfere with host cell function (Type III toxins)

An extracellular enzyme, Pseudomonas Exotoxin A is the most toxic virulence factor of the pathogenic bacterium Pseudomonas aeruginosa. It is a single-chain polypeptide (molecular weight, 71,000) with A and B fragments that mediate enzymatic and cell-binding functions, respectively.

P. aeruginosa is a common Gram-negative, rod-shaped bacterium, which is optimally adapted in various environmental conditions. P. aeruginosa is considered as one of the most important causative agents responsible for life-threatening systemic infections in the intensive care units and to the immuno­ compromised patients.

Virulence factor Pseudomonas Exotoxin A, enables P. aeruginosa to adhere to tissue surfaces, to damage tissue for dissemination and nutrition supply and to increase its survival rate. The infections range from endophtalmitis, endocarditis, meningitis, and septicemia to chronic lung infections.

Exotoxin A catalyses the transfer of the adenosine diphosphate-ribosyl moiety from nicotinamide-adenine dinucleotide to elongation factor 2, which results in the inactivation of the latter and the inhibition of protein biosynthesis. Exotoxin A is a potent cytotoxin and is lethal for a variety of animals, including subhuman primates.

The mature toxin is composed of three major functional domains: a receptor binding domain, a translocation domain, and a catalytic domain.
Pseudomonas Exotoxin A

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