Human α-Defensin-6 Neutralizes Clostridioides difficile Toxins TcdA and TcdB by Direct Binding

• Published in: International journal of molecular sciences 2022-04, Vol.23 (9), p.4509
• Main Authors: Barthold, Lara, Heber, Sebastian, Schmidt, Christoph Q, Gradl, Marion, Weidinger, Gilbert, Barth, Holger, Fischer, Stephan
• Format: Article
• Language: English
• Subjects: Actin; Aggregates; alpha-Defensins - pharmacology; Animals; Anti-Bacterial Agents - pharmacology; Antibiotics; Antibodies, Bacterial; Antiinfectives and antibacterials; Antimicrobial peptides; bacterial AB-type protein toxins; Bacterial Proteins - metabolism; Bacterial Toxins - metabolism; Binding; Biocompatibility; Cell cycle; Clostridioides difficile; Clostridioides difficile infections; Clostridium Infections - microbiology; Cytotoxicity; Embryos; Enterotoxins - chemistry; Exotoxins; Fluorescence; Guanine nucleotide-binding protein; human antimicrobial peptide; Humans; Infections; Intoxication; large clostridial glucosylating toxins TcdA and TcdB; Medical treatment; Morphology; Pathogens; Peptides; rho GTP-Binding Proteins - metabolism; Rounding; Signs and symptoms; Toxin A; toxin inhibitor; Toxins; Virulence; Virulence factors; Zebrafish; Zebrafish - metabolism; α-defensin-6
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms23094509

Rising incidences and mortalities have drawn attention to infections (CDIs) in recent years. The main virulence factors of this bacterium are the exotoxins TcdA and TcdB, which glucosylate Rho-GTPases and thereby inhibit Rho/actin-mediated processes in cells. This results in cell rounding, gut barrier disruption and characteristic clinical symptoms. So far, treatment of CDIs is limited and mainly restricted to some antibiotics, often leading to a vicious circle of antibiotic-induced disease recurrence. Here, we demonstrate the protective effect of the human antimicrobial peptide α-defensin-6 against TcdA, TcdB and the combination of both toxins in vitro and in vivo and unravel the underlying molecular mechanism. The defensin prevented toxin-mediated glucosylation of Rho-GTPases in cells and protected human cells, model epithelial barriers as well as zebrafish embryos from toxic effects. In vitro analyses revealed direct binding to TcdB in an SPR approach and the rapid formation of TcdB/α-defensin-6 complexes, as analyzed with fluorescent TcdB by time-lapse microscopy. In conclusion, the results imply that α-defensin-6 rapidly sequesters the toxin into complexes, which prevents its cytotoxic activity. These findings extend the understanding of how human peptides neutralize bacterial protein toxins and might be a starting point for the development of novel therapeutic options against CDIs.