Translocation domain mutations affecting cellular toxicity identify the Clostridium difficile toxin B pore

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Clostridium difficile toxins (TcdA, TcdB) cause disease by targeting colonic epithelial cells.
• Toxin internalization and pore formation are critical for cytosolic delivery of cytotoxic domains.

Purpose of the Study:

• To elucidate the mechanism of transmembrane pore formation by Clostridium difficile toxin B (TcdB).
• To identify key residues and structural elements involved in TcdB translocation into host cells.

Main Methods:

• Systematic mutagenesis of conserved residues within the TcdB translocation domain.
• Assessment of cellular toxicity and pore formation in lipid bilayers for mutant variants.

Main Results:

• Identified a critical region (amino acids 1,035–1,107) in the TcdB translocation domain essential for pore formation.
• Mutations in this region drastically reduced cellular toxicity (>1,000-fold) by impairing pore formation.
• Defective variants failed to intoxicate cells via apoptotic or necrotic pathways.

Conclusions:

• The identified 'hotspot' residues are crucial for TcdB pore formation and membrane translocation.
• Structural similarities exist between TcdB and diphtheria toxin translocation domains.
• Findings provide mechanistic insights into the pore formation and cell intoxication by pathogenic toxins.