Special Issue "A-B Type of Toxins: Mode of Transport and Interaction with Lipid Bilayers"

A special issue of Toxins (ISSN 2072-6651). This special issue belongs to the section "Bacterial Toxins".

Deadline for manuscript submissions: 10 November 2021.

Special Issue Editor

Prof. Roland Benz
E-Mail Website
Guest Editor
Department of Life Sciences and Chemistry, Jacobs-University Bremen, Campus-Ring 1, 28759 Bremen, Germany
Interests: porins of gram-negative bacteria; cell wall channels of the mycolate; cytolytic toxins from gram-negative bacteria; A-B type of toxins of gram-positive bacteria; clostridial toxins; pore-forming toxins from gram-positive bacteria
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Special Issue Information

Dear Colleagues, 

A-B types of toxins (so-called binary toxins) are potent virulence factors of certain Gram-positive bacteria. They consist of an enzymatic subunit A that is, in many cases, able to kill target cells by its enzymatic activity. The subunit B is secreted separately by the bacteria. It represents the binding/translocation subunit needed for the binding of toxins to target cells, and is responsible for the translocation of the enzymatic subunits into the cells via endosomal pathways. The most prominent example of this type of toxins is the tripartite anthrax toxin produced by Bacillus anthracis, which is listed by the World Health Organization (WHO) as a possible biological weapon. It consists of a binding protein, termed ‘protective antigen’, and two enzymatic subunits, the lethal factor and the edema factor, that are both able to kill target cells. Other prominent examples for A-B types of toxins are C2-toxin of Clostridium botulinum and Iota-toxin of Clostridium perfringens. Both toxins consist also of two distinct subunits that are secreted separately into the extracellular media: Component A is an actin-specific ADP-ribosyltransferase that is transported via component B into the target cells. After proteolytic activation, the binding components form ring-shaped heptamers. They form channels that mediate the transport of the enzymatic subunits of all A-B types of toxins into target cells via endosomal pathways. Reconstituted in lipid bilayers, the heptamers form cation-selective channels that can be blocked by interaction with the enzymatic subunits. They can also be blocked by positively charged heterocyclic molecules, such as chloroquine and related compounds. In vivo experiments also revealed that the same molecules inhibit intoxication by A-B types of toxins. The block of intoxication of target cells by compounds that bind to the heptamers is of considerable interest because of the possible use of A-B type of toxins as biological weapons.

Prof. Roland Benz
Guest Editor

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Keywords

  • A-B type of toxins
  • anthrax
  • C2-toxin
  • Iota-toxin
  • binding components
  • aminoquinolinium salts
  • black lipid bilayer
  • channel formation
  • channel block
  • block of intoxication

Published Papers (1 paper)

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Research

Article
Characterization and Pharmacological Inhibition of the Pore-Forming Clostridioides difficile CDTb Toxin
Toxins 2021, 13(6), 390; https://0-doi-org.brum.beds.ac.uk/10.3390/toxins13060390 - 28 May 2021
Viewed by 1146
Abstract
The clinically highly relevant Clostridioides (C.) difficile releases several AB-type toxins that cause diseases such as diarrhea and pseudomembranous colitis. In addition to the main virulence factors Rho/Ras-glycosylating toxins TcdA and TcdB, hypervirulent strains produce the binary AB-type toxin CDT. CDT [...] Read more.
The clinically highly relevant Clostridioides (C.) difficile releases several AB-type toxins that cause diseases such as diarrhea and pseudomembranous colitis. In addition to the main virulence factors Rho/Ras-glycosylating toxins TcdA and TcdB, hypervirulent strains produce the binary AB-type toxin CDT. CDT consists of two separate proteins. The binding/translocation B-component CDTb facilitates uptake and translocation of the enzyme A-component CDTa to the cytosol of cells. Here, CDTa ADP-ribosylates G-actin, resulting in depolymerization of the actin cytoskeleton. We previously showed that CDTb exhibits cytotoxicity in the absence of CDTa, which is most likely due to pore formation in the cytoplasmic membrane. Here, we further investigated this cytotoxic effect and showed that CDTb impairs CaCo-2 cell viability and leads to redistribution of F-actin without affecting tubulin structures. CDTb was detected at the cytoplasmic membrane in addition to its endosomal localization if CDTb was applied alone. Chloroquine and several of its derivatives, which were previously identified as toxin pore blockers, inhibited intoxication of Vero, HCT116, and CaCo-2 cells by CDTb and CDTb pores in vitro. These results further strengthen pore formation by CDTb in the cytoplasmic membrane as the underlying cytotoxic mechanism and identify pharmacological pore blockers as potent inhibitors of cytotoxicity induced by CDTb and CDTa plus CDTb. Full article
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