The Conformational Variability of FimH: Which Conformation Represents the Therapeutic Target?

Abstract

FimH is a bacterial lectin found at the tips of type 1 pili of uropathogenic Escherichia coli (UPEC). It mediates shear-enhanced adhesion to mannosylated surfaces. Binding of UPEC to urothelial cells initiates the infection cycle leading to urinary tract infections (UTIs). Antiadhesive glycomimetics based on α-d-mannopyranose offer an attractive alternative to the conventional antibiotic treatment because they do not induce a selection pressure and are therefore expected to have a reduced resistance potential. Genetic variation of the fimH gene in clinically isolated UPEC has been associated with distinct mannose binding phenotypes. For this reason, we investigated the mannose binding characteristics of four FimH variants with mannose-based ligands under static and hydrodynamic conditions. The selected FimH variants showed individually different binding behavior under both sets of conditions as a result of the conformational variability of FimH. Clinically relevant FimH variants typically exist in a dynamic conformational equilibrium. Additionally, we evaluated inhibitory potencies of four FimH antagonists representing different structural classes. Inhibitory potencies of three of the tested antagonists were dependent on the binding phenotype and hence on the conformational equilibrium of the FimH variant. However, the squarate derivative was the notable exception and inhibited FimH variants irrespective of their binding phenotype. Information on antagonist affinities towards various FimH variants has remained largely unconsidered despite being essential for successful antiadhesion therapy.

Genetic Diversity and Virulence Determinants of Escherichia coli Strains Isolated from Patients with Crohn's Disease in Spain and Chile

“…Some of the mutations reported here, such as V27A, N70S, and S78N, have been previously reported in UPEC strains. These polymorphisms are considered to be potential patho-adaptations that may confer significant advantages in regards to bacterial epithelial colonization (Eris et al, 2016). Such patho-adaptative polymorphisms were also observed in E. coli strains obtained from pediatric patients with inflammatory bowel disease (IBD) (Iebba et al, 2012).…”

Rational design strategies for FimH antagonists: new drugs on the horizon for urinary tract infection and Crohn’s disease

“…Furthermore, ligand or mannoside binding to FimH shifts its pre-existing equilibrium toward the high-affinity R state while occluding the mannose binding pocket and inhibiting host-pathogen interactions. Reports from several other groups [54-55, 93-94]postulate that urine flow in the bladder kinetically selects the rapidly-associating low-affinity conformation of FimH for receptor binding and that shear stress converts this bound low-affinity conformation to a bound high-affinity conformation of FimH. While the in vivo relevance of shear stress to human UTI remains unclear, these structural studies suggest that mannosides can in fact target both the low-affinity T state in addition to the high-affinity R state.…”

“…These studies are based on only a few FimH mannoside ligands[54], but the data suggests that individual mannosides can bind to these different states with significantly different affinities, while others bind with equal affinity to both the high affinity R and low affinity T conformations. It has also been shown that mannosides can bind with different affinities under “flow” or “non-flow” conditions as determined from in vitro assays [95-97].…”

Improvement of Aglycone π‐Stacking Yields Nanomolar to Sub‐nanomolar FimH Antagonists

“…Intermediate states and a high variability of the conformational ensemble have been described . Although all conformational states of FimH play a relevant role for the pathogenicity of UPEC, efforts for the development of therapeutic FimH antagonists have almost exclusively been focused on the high‐affinity state of the protein …”