Intervening with Urinary Tract Infections Using Anti-Adhesives Based on the Crystal Structure of the FimH–Oligomannose-3 Complex

Abstract

Background Escherichia coli strains adhere to the normally sterile human uroepithelium using type 1 pili, that are long, hairy surface organelles exposing a mannose-binding FimH adhesin at the tip. A small percentage of adhered bacteria can successfully invade bladder cells, presumably via pathways mediated by the high-mannosylated uroplakin-Ia and α3β1 integrins found throughout the uroepithelium. Invaded bacteria replicate and mature into dense, biofilm-like inclusions in preparation of fluxing and of infection of neighbouring cells, being the major cause of the troublesome recurrent urinary tract infections.Methodology/Principal FindingsWe demonstrate that α-d-mannose based inhibitors of FimH not only block bacterial adhesion on uroepithelial cells but also antagonize invasion and biofilm formation. Heptyl α-d-mannose prevents binding of type 1-piliated E. coli to the human bladder cell line 5637 and reduces both adhesion and invasion of the UTI89 cystitis isolate instilled in mouse bladder via catheterization. Heptyl α-d-mannose also specifically inhibited biofilm formation at micromolar concentrations. The structural basis of the great inhibitory potential of alkyl and aryl α-d-mannosides was elucidated in the crystal structure of the FimH receptor-binding domain in complex with oligomannose-3. FimH interacts with Manα1,3Manβ1,4GlcNAcβ1,4GlcNAc in an extended binding site. The interactions along the α1,3 glycosidic bond and the first β1,4 linkage to the chitobiose unit are conserved with those of FimH with butyl α-d-mannose. The strong stacking of the central mannose with the aromatic ring of Tyr48 is congruent with the high affinity found for synthetic inhibitors in which this mannose is substituted for by an aromatic group.Conclusions/SignificanceThe potential of ligand-based design of antagonists of urinary tract infections is ruled by the structural mimicry of natural epitopes and extends into blocking of bacterial invasion, intracellular growth and capacity to fluxing and of recurrence of the infection.

Cutting Edge: FimH Adhesin of Type 1 Fimbriae Is a Novel TLR4 Ligand

“…FimH is located at the tip and is involved in recognition by mannose. Recent crystal structure determination of FimH complexed with oligomannose-3 highlighted the feasibility of using natural and engineered mannose antagonists to block bacterial invasion and growth and biofilm formation (18). Previous studies using intact UPEC showed that both P and type 1 fimbriae signal through TLR4 to elicit chemokine production and neutrophil infiltration (6).…”

Recognition of Blood Group ABH Type 1 Determinants by the FedF Adhesin of F18-fimbriated Escherichia coli

“…The role of the FedF adhesin in this binding process was defined by using a FedF-negative mutant strain (5). Knowledge of the F18R structure could provide better insights into the interactions between F18-fimbriated E. coli and the porcine gut, and may, additionally, lead to the design of potent inhibitors of adherence for use in antiadhesive therapy (16).…”

Glycoconjugates and Glycomimetics as Microbial Anti-Adhesives

“…Crystallographic studies [8] (pdb: 1UWF, 1TR7) showed that the lectin domain of the adhesin contains a relatively deep sugar-binding pocket lined by aromatic lipophylic residues at the rim (the tyrosine gate, formed by Tyr48, Tyr137 and Ile52) and established butyl α-D-mannoside 1 ( Figure 1a) as a strong antagonist. Optimization of the aglycone chain length led to the discovery of n-heptyl α-D-mannoside (α-D-HM, 2, Figure 1a) as a nanomolar FimH antagonist [9]. Recent structural studies [10] have called into question the importance of the tyrosine gate in the recognition process of mannosides by the full FimH protein.…”

“…The biochemical and structural data that have been accumulating on sugar-protein interactions, and the current ability to decipher the sequence and function of cell-associated glycans, will surely offer in the near future the possibility of developing novel tools to interfere in the infection process using materials that mimic the natural presentation of adhesion oligosaccharides. [8], heptyl α-D-mannoside (α-D-HM) 2 [9], 3 [13], 4 [15] and 5 [17] for antiadhesion therapy of urinary tract infections; FimH antagonist 6 [32,33] was developed for antiadhesion of AIEC to intestinal cells; b) Surface functionalization of small NDs 5 by Diels-Alder reaction of an in situ generated o-quinodimethide [27]. The sugar 10 is grafted using a thiol-ene reaction [34]; c)…”