Blocking Vibrio cholerae-mediated hemagglutination with short peptide antagonists

Many bacteria use repeats-in-toxin (RTX) adhesins to mediate binding to host cells and facilitate subsequent colonisation and infection by forming biofilms. Vibrio cholerae, the causative agent of cholera, uses a 230-kDa RTX adhesin, FrhA, to facilitate intestinal colonization. FrhA also mediates hemagglutination of red-blood cells (erythrocytes). Here we have demonstrated that the hemagglutination capability of FrhA is localized to a ~ 20-kDa domain near its C terminus. Bioinformatic analyses indicated this erythrocyte-binding domain (VcEBD) is 65% identical to a peptide-binding module found in the 1.5-MDa ice-binding RTX adhesin that helps its Antarctic bacterium, Marinomonas primoryensis, form symbiotic biofilms with diatoms on the underside of sea ice. This suggested that the FrhA binds V. cholerae to proteins present on the cell surface of erythrocytes. X-ray crystallography revealed that VcEBD has an oblong β-sandwich fold with a shallow, Ca²⁺-dependent ligand-binding cavity that can anchor a peptidyl ligand with a free terminal carboxyl group. Using a structure-guided approach, we screened a small library of ~ 60 short peptides and optimized the affinity of VcEBD’s peptidyl ligands by roughly 1,000-fold. Importantly, the high-affinity ligands are effective at blocking V. cholerae from binding to erythrocytes at nano-molar concentrations. Structures of VcEBD in complex with three different peptides further elucidated the molecular basis for their interactions, which sets the stage for the development of ligand-based antagonists that may help disrupt V. cholerae interaction with intestinal cells to prevent or treat cholera. With the spread of antibiotic-resistant pathogenic bacteria, this work sheds light on an anti-adhesion approach for combating bacterial infections without the excessive use of antibiotics.