A sequence invariable region in TcdB2 is required for toxin escape from Clostridioides difficile

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Clostridioides difficile is a major cause of antibiotic-associated diarrhea.
• Toxins TcdA and TcdB are the primary virulence factors of C. difficile.
• TcdB exhibits sequence variants with differing functional properties.

Purpose of the Study:

• To investigate the functional role of a highly conserved, invariable region in the C-terminus of TcdB.
• To determine the importance of this conserved region for TcdB secretion and activity.

Main Methods:

• Construction and analysis of a C. difficile strain producing a truncated TcdB lacking the sequence invariable region (SIR).
• Assessment of TcdB mutant's enzymatic activity, cytopathic effects, and secretion.
• Cell fractionation and antibody detection to localize the truncated TcdB.

Main Results:

• The SIR domain is not required for TcdB's enzymatic or cytotoxic activity.
• TcdB lacking the SIR domain is retained within the bacterial cell and not secreted.
• The truncated TcdB accumulates at the cell membrane, indicating a role in toxin release.

Conclusions:

• The sequence invariable region (SIR) of TcdB is crucial for its efficient secretion from C. difficile.
• Conservation of the SIR domain across TcdB subtypes is likely driven by its role in toxin release.
• Understanding TcdB secretion mechanisms can inform strategies to combat C. difficile infections.