Urinary tract infections (UTI) belong to the most common infections worldwide and are predominantly caused by uropathogenic E. coli (UPEC). UPEC initiate the infection cycle by adhering to urothelial cells through the bacterial lectin FimH. Located at the tip of type 1 pili, FimH mediates adhesion by binding to high-mannose glycoproteins present on urothelial cells. Preventing the initial adhesion by blocking FimH with glycomimetic antagonists represents a promising alternative to the conventional antibiotic treatment of UTI, which has become increasingly inefficacious due to the aggravating issue of antibiotic resistance. The FimH-mannose interaction is peculiar in that it is shear stress dependent, meaning that FimH mediates weaker binding at low shear stress and stronger binding at high shear stress. This type of bond is called catch-bond and results from the ability of FimH to adopt two distinct bound conformations, a medium- and a high-affinity conformation. In the urinary tract, the shear stress-induced switch from the medium- to the high-affinity conformation becomes an effective tool for UPEC to evade clearance by the bulk flow of urine. So far, efforts in developing FimH antagonists have been predominantly focused on the high-affinity conformation, and the importance of the conformational heterogeneity of FimH has been mostly neglected. To this effect, we have investigated FimH binding of various clinically and functionally relevant FimH variants in a cell-based assay under hydrodynamic conditions. Clinical FimH variants were typically characterized by a catch-bond behavior. By studying bacterial binding in a cell motility assay, we were able to show that conformationally dynamic FimH variants are highly mobile on a mannosylated surface, allowing optimal colonization in the bladder. In addition, by switching to the high-affinity conformation, these bacteria can resist upcoming shear stress and are thus protected from being washed out through urination. In contrast, a variant with constitutive high-affinity also formed long-lived interactions with mannose in the absence of shear stress, rendering bacteria immobile. It becomes evident that dynamic FimH variants are pathophysiologically favored and represents the dominant therapeutic target. To further elucidate this conformational issue, antagonists with high binding affinities to both affinity states were synthesized and characterized in various in vitro and in vivo models.

Conformational variability of the bacterial lectin FimH: Which conformation represents the therapeutic target?

254th National Meeting (2017)

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