Structural basis of tropism of Escherichia coli to the bladder during urinary tract infection

Abstract

The first step in the colonization of the human urinary tract by pathogenic Escherichia coli is the mannose-sensitive binding of FimH, the adhesin present at the tip of type 1 pili, to the bladder epithelium. We elucidated crystallographically the interactions of FimH with D-mannose. The unique site binding pocket occupied by D-mannose was probed using site-directed mutagenesis. All but one of the mutants examined had greatly diminished mannose-binding activity and had also lost the ability to bind human bladder cells. The binding activity of the mono-saccharide D-mannose was delineated from this of mannotriose (Man(alpha 1-3)[Man(alpha 1-6)]Man) by generating mutants that abolished D-mannose binding but retained mannotriose binding activity. Our structure/function analysis demonstrated that the binding of the monosaccharide alpha-D-mannose is the primary bladder cell receptor for uropathogenic E. coli and that this event requires a highly conserved FimH binding pocket. The residues in the FimH mannose-binding pocket were sequenced and found to be invariant in over 200 uropathogenic strains of E. coli. Only enterohaemorrhagic E. coli (EHEC) possess a sequence variation within the mannose-binding pocket of FimH, suggesting a naturally occurring mechanism of attenuation in EHEC bacteria that would prevent them from being targeted to the urinary tract.

Positive selection identifies an in vivo role for FimH during urinary tract infection in addition to mannose binding

“…This binding is thought to be the primary molecular feature by which FimH supports UTI (1). Identified amino acid variation in FimH is restricted to 29 residues distributed throughout the protein structure, but the 8 amino acids making up its mannose-binding pocket (16) are invariant in all 188 UPEC strains we studied. Mutation of residues in the mannose binding pocket, such as Q133K, completely abolishes mannose binding activity (16).…”

“…The structural basis for FimH recognition of mannose is known (16). FimH-mediated binding to mannosylated receptors produced by urothelial cells is critical for UPEC to cause bladder infection (cystitis) (17,18), as it mediates colonization and invasion of superficial umbrella cells lining the luminal surface of the urothelium.…”

Catch Bond-mediated Adhesion without a Shear Threshold

“…Mutations in the 1M-binding Pocket Similarly Affect 1M-and 3M-specific Binding under Shear-To test further to what extent the 1M-binding subsite is involved in the 3M-specific interaction under shear, we modified some of the residues that constitute the 1M-binding site according to the crystal structure (18) and determined their effect on the 3M-specific binding under various shear stresses. Most of the 1M-binding residues are primarily clustered on two larger loops that form a hydrophobic ring around the FimH 1M-binding site, with the N terminus also contributing to the ligand interaction.…”

“…Most of the 1M-binding residues are primarily clustered on two larger loops that form a hydrophobic ring around the FimH 1M-binding site, with the N terminus also contributing to the ligand interaction. Most of the mutations tested here have been tested previously in static conditions only and in the shear-dependent FimH variant (from E. coli strain J96) with relatively weak 1M-binding under static conditions (18). Instead, we introduced these and other mutations into the background of the same FimH variant but with the V156P mutation that mediates a high level and strength of adhesion to both 1M and 3M ligands already in static conditions (see above).…”

“…FimH is a two-domain protein consisting of the mannose-binding lectin domain and the fimbria-incorporating pilin domain. On the top of the lectin domain, distal from the pilin domain, is the ligand-binding pocket that accommodates a 1M 3 residue (18). The ability of FimH to bind to 1M under static, no-flow conditions is a highly variable property.…”