Inhibitors and Countermeasures against Bacterial and Plant Toxins

A special issue of Toxins (ISSN 2072-6651).

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 21982

Special Issue Editors


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Guest Editor
Section of Molecular Engineering for Health (SIMoS), JOLIOT, CEA, Université Paris-Saclay, F-91191 Gif Sur Yvette, France
Interests: bacterial toxins; diphtheria toxin; ricin toxin; Shiga toxins; botulinum toxins; intracellular trafficking; biodefense; toxin inhibitors; antitoxin drug development
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Guest Editor
Service d'Ingénierie Moléculaire des Protéines (SIMOPRO), JOLIOT, CEA, Université Paris-Saclay, F-91191 Gif Sur Yvette, France
Interests: ricin; Shiga toxins; bacterial toxins; retrograde transport; toxin inhibitors
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Inhibitors of bacterial and plant toxins are used as research tools to understand the mechanism of action of toxins. Inhibitors also form the basis for the development of drugs to treat intoxications and bacterial infections. Thus, inhibitors are central to the field of toxinology.

During bacterial infections of host organisms, protein toxins are among the most important virulence factors used by the bacteria to invade, survive, and expand in a rich nutritive, but also hostile, environment. These toxins may contain all the components necessary to achieve their deleterious effects or can be effector proteins injected into host cells through diverse and complex secretion systems acting as transmembrane injectors. Microorganisms also fight each other with toxins to secure their existence in their ecological niche and protect themselves from their own toxins with natural inhibitors called antitoxins. Plants produce protein toxins that resemble bacterial toxins in their architecture and mechanisms of action. These toxins may play a role of defense against infection or predation. They are also the cause of accidental, voluntary or criminal poisoning.

There is an extraordinary diversity of bacterial and plant toxins. Likewise, there is a high diversity of toxin substrates and mechanisms leading to cellular perturbations. The actions of these toxins may include the perforation of membranes, the manipulation of the cytoskeleton and/or of signaling pathways, the diversion of protein trafficking, the impairment of neuromediator secretion, the inhibition of protein synthesis, the deregulation of transcription, the damaging of DNA, and many other effects. As a result, toxins may paralyze or kill cells, open cellular barriers, manipulate the host’s immune defenses to favor bacterial invasion or persistence in tissues, or kill the infected organism as a whole.

After less than a century of relative relief from mortal bacterial infections thanks to antibiotics, the development of bacterial strains resistant to multiple antibiotics has induced a re-emergence of infectious diseases. Infections become untreatable, inducing 700,000 deaths per year worldwide. Vaccines against toxins have helped to reduce dramatically the prevalence of a series of fatal bacterial diseases such as diphtheria, tetanus or whooping cough. However, lack of, or breaches in vaccination coverage result in the resurgence of these mortal diseases. In addition, some less frequent toxin infections never benefited from efficient treatment or vaccines. In the past, highly pathogenic bacterial and plant toxins as well as toxin-producing bacteria have been weaponized and used in warfare. They are now involved in terrorist threats and criminal or suicidal actions. Thus, altogether, there is an urgent need for countermeasures to neutralize and treat intoxications and infections involving bacterial and plant toxins.

This Special Issue proposes to highlight, through reviews, research articles, and communications, as well as opinion statements, novel concepts and molecular developments to inhibit the effects of bacterial and plant toxins and understand their mechanisms of action. Inhibitors and countermeasures are taken here in their broader meaning. They can be natural or synthetic small molecule inhibitors acting on toxins or on pathways exploited by toxins; they can be peptides, proteins, or of another chemical nature; they enclose monoclonal, polyclonal or engineered antibodies, vaccines, or other means to counteract the action of toxins. Contributions may address fundamental aspects, drug discovery and development, clinical evaluation or any other domains of toxinology.

Dr. Daniel Gillet
Dr. Julien Barbier
Guest Editors

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Keywords

  • Toxin Inhibitors;
  • Toxin countermeasures;
  • Bacterial infections;
  • Bacterial Toxin;
  • Plant toxins.

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Published Papers (5 papers)

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Research

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14 pages, 4802 KiB  
Article
Two VHH Antibodies Neutralize Botulinum Neurotoxin E1 by Blocking Its Membrane Translocation in Host Cells
by Kwok-Ho Lam, Kay Perry, Charles B. Shoemaker and Rongsheng Jin
Toxins 2020, 12(10), 616; https://doi.org/10.3390/toxins12100616 - 27 Sep 2020
Cited by 12 | Viewed by 3721
Abstract
Botulinum neurotoxin serotype E (BoNT/E) is one of the major causes of human botulism, which is a life-threatening disease caused by flaccid paralysis of muscles. After receptor-mediated toxin internalization into motor neurons, the translocation domain (HN) of BoNT/E transforms into a [...] Read more.
Botulinum neurotoxin serotype E (BoNT/E) is one of the major causes of human botulism, which is a life-threatening disease caused by flaccid paralysis of muscles. After receptor-mediated toxin internalization into motor neurons, the translocation domain (HN) of BoNT/E transforms into a protein channel upon vesicle acidification in endosomes and delivers its protease domain (LC) across membrane to enter the neuronal cytosol. It is believed that the rapid onset of BoNT/E intoxication compared to other BoNT serotypes is related to its swift internalization and translocation. We recently identified two neutralizing single-domain camelid antibodies (VHHs) against BoNT/E1 termed JLE-E5 and JLE-E9. Here, we report the crystal structures of these two VHHs bound to the LCHN domain of BoNT/E1. The structures reveal that these VHHs recognize two distinct epitopes that are partially overlapping with the putative transmembrane regions on HN, and therefore could physically block membrane association of BoNT/E1. This is confirmed by our in vitro studies, which show that these VHHs inhibit the structural change of BoNT/E1 at acidic pH and interfere with BoNT/E1 association with lipid vesicles. Therefore, these two VHHs neutralize BoNT/E1 by preventing the transmembrane delivery of LC. Furthermore, structure-based sequence analyses show that the 3-dimensional epitopes of these two VHHs are largely conserved across many BoNT/E subtypes, suggesting a broad-spectrum protection against the BoNT/E family. In summary, this work improves our understanding of the membrane translocation mechanism of BoNT/E and paves the way for developing VHHs as diagnostics or therapeutics for the treatment of BoNT/E intoxication. Full article
(This article belongs to the Special Issue Inhibitors and Countermeasures against Bacterial and Plant Toxins)
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18 pages, 3237 KiB  
Article
Camelid VHH Antibodies that Neutralize Botulinum Neurotoxin Serotype E Intoxication or Protease Function
by Jacqueline M. Tremblay, Edwin Vazquez-Cintron, Kwok-Ho Lam, Jean Mukherjee, Daniela Bedenice, Celinia A. Ondeck, Matthieu T. Conroy, Skylar M. L. Bodt, Brittany M. Winner, Robert P. Webb, Konstantin Ichtchenko, Rongsheng Jin, Patrick M. McNutt and Charles B. Shoemaker
Toxins 2020, 12(10), 611; https://doi.org/10.3390/toxins12100611 - 24 Sep 2020
Cited by 14 | Viewed by 3807
Abstract
Botulinum neurotoxin (BoNT) serotype E is one of three serotypes that cause the preponderance of human botulism cases and is a Tier 1 Select Agent. BoNT/E is unusual among BoNT serotypes for its rapid onset and short duration of intoxication. Here we report [...] Read more.
Botulinum neurotoxin (BoNT) serotype E is one of three serotypes that cause the preponderance of human botulism cases and is a Tier 1 Select Agent. BoNT/E is unusual among BoNT serotypes for its rapid onset and short duration of intoxication. Here we report two large panels of unique, unrelated camelid single-domain antibodies (VHHs) that were selected for their ability to bind to BoNT/E holotoxin and/or to the BoNT/E light chain protease domain (LC/E). The 19 VHHs which bind to BoNT/E were characterized for their subunit specificity and 8 VHHs displayed the ability to neutralize BoNT/E intoxication of neurons. Heterodimer antitoxins consisting of two BoNT/E-neutralizing VHHs, including one heterodimer designed using structural information for simultaneous binding, were shown to protect mice against co-administered toxin challenges of up to 500 MIPLD50. The 22 unique VHHs which bind to LC/E were characterized for their binding properties and 9 displayed the ability to inhibit LC/E protease activity. Surprisingly, VHHs selected on plastic-coated LC/E were virtually unable to recognize soluble or captured LC/E while VHHs selected on captured LC/E were poorly able to recognize LC/E coated to a plastic surface. This panel of anti-LC/E VHHs offer insight into BoNT/E function, and some may have value as components of therapeutic antidotes that reverse paralysis following BoNT/E exposures. Full article
(This article belongs to the Special Issue Inhibitors and Countermeasures against Bacterial and Plant Toxins)
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14 pages, 1628 KiB  
Article
A Humanized Monoclonal Antibody Cocktail to Prevent Pulmonary Ricin Intoxication
by Yinghui Rong, Michael Pauly, Adrian Guthals, Henry Pham, Dylan Ehrbar, Larry Zeitlin and Nicholas J. Mantis
Toxins 2020, 12(4), 215; https://doi.org/10.3390/toxins12040215 - 29 Mar 2020
Cited by 15 | Viewed by 3425
Abstract
PB10 IgG1, a monoclonal antibody (MAb) directed against an immunodominant epitope on the enzymatic subunit (RTA) of ricin toxin (RT), has been shown to passively protect mice and non-human primates from an aerosolized lethal-dose RT challenge. However, it was recently demonstrated [...] Read more.
PB10 IgG1, a monoclonal antibody (MAb) directed against an immunodominant epitope on the enzymatic subunit (RTA) of ricin toxin (RT), has been shown to passively protect mice and non-human primates from an aerosolized lethal-dose RT challenge. However, it was recently demonstrated that the therapeutic efficacy of PB10 IgG1 is significantly improved when co-administered with a second MAb, SylH3, targeting RT’s binding subunit (RTB). Here we report that the PB10/SylH3 cocktail is also superior to PB10 alone when used as a pre-exposure prophylactic (PrEP) in a mouse model of intranasal RT challenge. The benefit of the PB10/SylH3 cocktail prompted us to engineer a humanized IgG1 version of SylH3 (huSylH3). The huPB10/huSylH3 cocktail proved highly efficacious in the mouse model, thereby opening the door to future testing in non-human primates. Full article
(This article belongs to the Special Issue Inhibitors and Countermeasures against Bacterial and Plant Toxins)
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13 pages, 4908 KiB  
Article
Revisiting Old Ionophore Lasalocid as a Novel Inhibitor of Multiple Toxins
by Nassim Mahtal, Yu Wu, Jean-Christophe Cintrat, Julien Barbier, Emmanuel Lemichez and Daniel Gillet
Toxins 2020, 12(1), 26; https://doi.org/10.3390/toxins12010026 - 1 Jan 2020
Cited by 10 | Viewed by 3809
Abstract
The ionophore lasalocid is widely used as a veterinary drug against coccidiosis. We found recently that lasalocid protects cells from two unrelated bacterial toxins, the cytotoxic necrotizing factor-1 (CNF1) from Escherichia. coli and diphtheria toxin. We evaluated lasalocid’s capacity to protect cells against [...] Read more.
The ionophore lasalocid is widely used as a veterinary drug against coccidiosis. We found recently that lasalocid protects cells from two unrelated bacterial toxins, the cytotoxic necrotizing factor-1 (CNF1) from Escherichia. coli and diphtheria toxin. We evaluated lasalocid’s capacity to protect cells against other toxins of medical interest comprising toxin B from Clostridium difficile, Shiga-like toxin 1 from enterohemorrhagic E. coli and exotoxin A from Pseudomonas aeruginosa. We further characterized the impact of lasalocid on the endolysosomal and the retrograde pathways and organelle integrity, especially the Golgi apparatus. We found that lasalocid protects cells from all toxins tested and impairs the drop of vesicular pH along the trafficking pathways that are required for toxin sorting and translocation to the cytoplasm. Lasalocid also has an impact on the cellular distribution of GOLPH4 and GOLPH2 Golgi markers. Other intracellular trafficking compartments positive for EEA1 and Rab9A display a modified cellular pattern. In conclusion, lasalocid protects cells from multiple deadly bacterial toxins by corrupting vesicular trafficking and Golgi stack homeostasis. Full article
(This article belongs to the Special Issue Inhibitors and Countermeasures against Bacterial and Plant Toxins)
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Review

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15 pages, 2335 KiB  
Review
Targeting the Early Endosome-to-Golgi Transport of Shiga Toxins as a Therapeutic Strategy
by Danyang Li, Andrey Selyunin and Somshuvra Mukhopadhyay
Toxins 2020, 12(5), 342; https://doi.org/10.3390/toxins12050342 - 22 May 2020
Cited by 11 | Viewed by 5577
Abstract
Shiga toxin (STx) produced by Shigella and closely related Shiga toxin 1 and 2 (STx1 and STx2) synthesized by Shiga toxin-producing Escherichia coli (STEC) are bacterial AB5 toxins. All three toxins target kidney cells and may cause life-threatening renal disease. While Shigella [...] Read more.
Shiga toxin (STx) produced by Shigella and closely related Shiga toxin 1 and 2 (STx1 and STx2) synthesized by Shiga toxin-producing Escherichia coli (STEC) are bacterial AB5 toxins. All three toxins target kidney cells and may cause life-threatening renal disease. While Shigella infections can be treated with antibiotics, resistance is increasing. Moreover, antibiotic therapy is contraindicated for STEC, and there are no definitive treatments for STEC-induced disease. To exert cellular toxicity, STx, STx1, and STx2 must undergo retrograde trafficking to reach their cytosolic target, ribosomes. Direct transport from early endosomes to the Golgi apparatus is an essential step that allows the toxins to bypass degradative late endosomes and lysosomes. The essentiality of this transport step also makes it an ideal target for the development of small-molecule inhibitors of toxin trafficking as potential therapeutics. Here, we review the recent advances in understanding the molecular mechanisms of the early endosome-to-Golgi transport of STx, STx1, and STx2, as well as the development of small-molecule inhibitors of toxin trafficking that act at the endosome/Golgi interface. Full article
(This article belongs to the Special Issue Inhibitors and Countermeasures against Bacterial and Plant Toxins)
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