A peptidomimetic inhibitor blocks Vibrio cholerae adhesin FrhA

Cholera is a diarrheal disease resulting from colonization of the small intestine by the Gram-negative bacterium Vibrio cholerae . The peptide-binding domain (PBD) of the adhesion protein FrhA is critical for V. cholerae intestinal colonization and biofilm formation. In a program aimed at blocking cholera infection, antagonists of the FrhA-PBD are described based on a tripeptide motif, such as H-Trp-Thr-Asp-OH. Notably, constraining the N-terminal tryptophan residue using 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (Tcc) and co-crystallization of H-(S)-Tcc-Thr-Asp-OH with a FrhA construct have provided structural information to guide inhibitor design. The diastereomer H-(R)-Tcc-Thr-Asp-OH exhibited nanomolar binding affinity K _d = 101 ± 30.2 nM), blocked bacterial hemagglutination mediated by FrhA-PBD, and reduced biofilm formation in vitro. It also inhibited intestinal epithelial cell adhesion to an immobilized recombinant FrhA-PBD construct (IC□□ = 24 µM; 95% CI, 11–51 µM). Its resistance to chymotrypsin proteolysis supports further investigation as an anti-adhesion peptidomimetic.