Structural Basis for Binding of Neutralizing Antibodies to Clostridioides difficile Binary Toxin

Area of Science:

• Microbiology
• Immunology
• Structural Biology

Background:

• Clostridioides difficile is a major cause of infectious diarrhea, with binary toxin (CDT) contributing to severe disease.
• Understanding CDT neutralization mechanisms is crucial for developing effective vaccines and therapeutics.

Purpose of the Study:

• To isolate and characterize neutralizing monoclonal antibodies against CDT.
• To elucidate the structural and biochemical mechanisms by which these antibodies inhibit CDT activity.

Main Methods:

• Isolation of neutralizing monoclonal antibodies against CDT.
• X-ray crystallography to determine antibody-CDT complex structures at high resolution.
• In vitro assessment of antibody effects on CDT protoxin oligomerization.

Main Results:

• Two neutralizing antibodies, BINTOXB/22 and BINTOXB/9, were identified.
• Crystal structures revealed antibodies sterically hinder CDTb heptamer assembly.
• Antibodies prevented CDTb oligomerization in vitro, blocking toxin activation.

Conclusions:

• Antibody-mediated steric hindrance of CDT oligomerization is a viable neutralization mechanism.
• Targeting CDT oligomerization is a promising strategy for C. difficile vaccine and therapeutic development.