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. Antagonists of the FrhA-PBD were designed based on the tripeptide motif H-Trp-Thr-Asp-OH. Constraining the N-terminal tryptophan as a 1,2,3,4-tetrahydro-{beta}-carboline-3-carboxylic acid (Tcc) residue and X-ray analysis of a co-crystal with the FrhA-PBD define the minimal inhibitory motif. Moreover, H-(R)-Tcc-Thr-Asp-OH exhibited nanomolar binding affinity (Kd = 101 {+/-} 30.2 nM) to the FrhA-PBD, blocking adhesion protein-mediated bacterial hemagglutination and reducing biofilm formation in vitro. Intestinal epithelial cell adhesion to the FrhA-PBD was also blocked by the Tcc tripeptide (IC50 = 24 M; 95% CI, 11-51 M), which resisted chymotrypsin proteolysis. The activity of this peptidomimetic inhibitor and the atomic-level understanding of FrhA-PBD binding provide insights for developing anti-adhesion therapies to treat cholera.