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Updated: Oct 16, 2025

Detection of Toxin Translocation into the Host Cytosol by Surface Plasmon Resonance
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Structural basis for selective modification of Rho and Ras GTPases by Clostridioides difficile toxin B

Zheng Liu1, Sicai Zhang2, Peng Chen1

  • 1Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA 92697, USA.

Science Advances
|October 22, 2021
PubMed

Insights

Toxin B, a cause of Clostridioides difficile infection (CDI), targets Rho GTPases. Structural studies reveal how Toxin B recognizes its targets, offering new strategies for CDI therapies.

Area of Science:

  • Molecular biology
  • Structural biology
  • Microbiology

Background:

  • Clostridioides difficile infection (CDI) is a significant healthcare concern, primarily caused by Toxin B (TcdB).
  • TcdB functions by glucosylating small GTPases, but the precise structural mechanisms of substrate recognition and selectivity are not fully understood.

Purpose of the Study:

  • To elucidate the structural basis of TcdB recognition and selectivity for its small GTPase substrates.
  • To identify key residues and mechanisms governing TcdB substrate specificity.

Main Methods:

  • Cocrystallization of the TcdB glucosyltransferase domain (GTD) with human Cdc42 and R-Ras.
  • X-ray crystallography to determine the complex structures.
  • Site-directed mutagenesis to investigate the role of specific residues.

Main Results:

  • Determined cocrystal structures of TcdB GTD variants with Cdc42 and R-Ras, revealing a conserved recognition mechanism.
  • Identified adaptive residue variations within GTDs that dictate substrate specificity, classifying TcdB variants into two distinct groups.
  • Demonstrated that mutations disrupting GTPase binding reduce GTD activity and TcdB holotoxin toxicity.

Conclusions:

  • Established the structural foundation for TcdB's interaction with Rho/Ras family GTPases.
  • Uncovered how TcdB variants achieve distinct substrate specificities.
  • Provided insights into potential therapeutic strategies targeting TcdB for CDI treatment.

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