(150e) Design of Peptides to Inhibit Multiple Clostridium Difficile toxin B Subtypes in the Presence of UDP-Glucose and Mn2+

Clostridium difficile (C. diff) infections cause diarrhea and severe colitis. C. diff kills 30,000 out of the 500,000 people it affects every year in the United States. Current antibiotic treatments are not always effective due to antibiotic resistance. Short peptides are being considered as potential drug candidates to prevent and treat C. diff infection by inhibiting the biocatalytic activity of the two toxins, TcdA and TcdB, released by the bacterium. These toxins transfer glucose from UDP-Glucose to Rho/Rac family proteins, leading to the death of colonic epithelial cells. In our group’s previous efforts, a solid-phase peptide screening library and the Peptide Binding Design (PepBD) algorithm were used to design peptides to prevent the binding of UDP-Glucose to TcdB. Interestingly, one of the most effective peptides identified, SB5, was found experimentally to bind to a different site than the one where UDP-Glucose binds. Instead, this peptide bound to the site on TcdB where the Rho/Rac protein binds, thus preventing cell death by preventing the Rho/Rac family proteins from being glycosylated. We aim to determine how SB5 binds to the TcdB1 and TcdB3 subtypes when UDP-Glucose and Mn²⁺ are already bound since UDP-Glucose and Mn²⁺ are both present on TcdB in cellular environments. This may help us to design peptides with a lower binding free energy to multiple TcdB subtypes than the SB5 peptide. We have applied a computational approach that combines explicit-solvent atomistic molecular dynamics simulations and the PepBD algorithm to design new and more-effective peptides for combating C. diff infections.