Urinary tract infections (UTI) caused by uropathogenic E. coli (UPEC) are among the most common bacterial infections. To date, patients with acute uncomplicated lower UTI are treated with antibiotics to relieve them from infection related symptoms and to prevent exacerbation into life-threatening pyelonephritis or urosepsis. However, the repeated use of antibiotics as a first-line treatment provokes resistance, underlining the need for new strategies to prevent and treat UTI.
The bacterial adhesin FimH, an important virulence factor of UPEC, is located at the distal tip of type 1 pili of uropathogenic E. coli strains (UPECs), which are the major cause of urinary tract infections (UTI). In the initial step of infection, bacteria only weakly interact with the host cell surfaces, still allowing their exploration for optimal nutrition supply. However, when shear forces arise, strong adherence to host cells is necessary to avoid clearance from the bladder. To fulfill these two opposing tasks, FimH relies on a sophisticated allosteric mechanism, fine-tuning its mannose binding affinity according the current requirements through conformational adaption.
Here, we show that the binding affinity, kinetics, and thermodynamics of glycomimetic antagonists to FimH are greatly affected by the conformational dynamics of the protein. Isothermal titration calorimetry (ITC) experiments reveal that strong enthalpy–entropy compensation effects dominate the thermodynamic binding profiles. Kinetic data derived from kinITC analysis gives additional insight into the molecular mechanism of protein–ligand interaction.
Furthermore, we present a series of novel FimH antagonists with high affinity to both disease relevant conformations. Crystallographic and NMR spectroscopic experiments reveal that their unprecedented affinity in the nano- to subnanomolar range is driven by strong π-stacking interactions with the tyrosine gate of FimH. In combination with in vitro pharmacokinetic properties indicative for oral bioavailability, the presented antagonists constitute exhibit promising characteristics for an antiadhesive therapy of UTI.