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Published on: December 15, 2017
Mucoricin is a ricin-like toxin that is critical for the pathogenesis of mucormycosis
Sameh S M Soliman1,2, Clara Baldin1,3, Yiyou Gu1
1Division of Infectious Diseases, The Lundquist Institute for Biomedical Innovation, Harbor-University of California at Los Angeles (UCLA) Medical Center, Torrance, CA, USA.
Abstract:
Fungi of the order Mucorales cause mucormycosis, a lethal infection with an incompletely understood pathogenesis. We demonstrate that Mucorales fungi produce a toxin, which plays a central role in virulence. Polyclonal antibodies against this toxin inhibit its ability to damage human cells in vitro and prevent hypovolemic shock, organ necrosis and death in mice with mucormycosis. Inhibition of the toxin in Rhizopus delemar through RNA interference compromises the ability of the fungus to damage host cells and attenuates virulence in mice. This 17 kDa toxin has structural and functional features of the plant toxin ricin, including the ability to inhibit protein synthesis through its N-glycosylase activity, the existence of a motif that mediates vascular leak and a lectin sequence. Antibodies against the toxin inhibit R. delemar- or toxin-mediated vascular permeability in vitro and cross react with ricin. A monoclonal anti-ricin B chain antibody binds to the toxin and also inhibits its ability to cause vascular permeability. Therefore, we propose the name 'mucoricin' for this toxin. Not only is mucoricin important in the pathogenesis of mucormycosis but our data suggest that a ricin-like toxin is produced by organisms beyond the plant and bacterial kingdoms. Importantly, mucoricin should be a promising therapeutic target.
Insights
Mucorales fungi produce a lethal toxin, named mucoricin, crucial for virulence in mucormycosis. Antibodies targeting mucoricin show therapeutic potential by neutralizing its damaging effects and preventing lethal outcomes in animal models.
Area of Science:
- Mycology
- Infectious Diseases
- Toxicology
Background:
- Mucormycosis is a lethal fungal infection caused by Mucorales fungi with poorly understood pathogenesis.
- Virulence factors of Mucorales fungi are critical for disease development and patient outcomes.
Purpose of the Study:
- To identify and characterize the key virulence factor produced by Mucorales fungi.
- To investigate the therapeutic potential of targeting this virulence factor in mucormycosis.
Main Methods:
- Identification and purification of a fungal toxin from Mucorales.
- In vitro assays using human cells to assess toxin-induced damage.
- In vivo studies in mice to evaluate the efficacy of anti-toxin antibodies and RNA interference.
- Structural and functional analysis of the toxin, comparing it to known toxins like ricin.
Main Results:
- A 17 kDa toxin, named mucoricin, was identified as a major virulence factor.
- Mucoricin inhibits protein synthesis via N-glycosylase activity and causes vascular leak.
- Polyclonal antibodies against mucoricin neutralized its cytotoxic effects and protected mice from mucormycosis.
- RNA interference targeting mucoricin production attenuated fungal virulence in vitro and in vivo.
- Mucoricin shares structural and functional similarities with the plant toxin ricin.
Conclusions:
- Mucoricin is a critical virulence factor in mucormycosis, acting similarly to ricin.
- Targeting mucoricin with antibodies represents a promising therapeutic strategy for invasive fungal infections.
- The discovery of mucoricin expands our understanding of toxin production across different kingdoms of life.
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