Conformational Basis and Small Molecule Antagonists of E. coli Adhesion to the Urinary Tract

Urinary tract infections (UTIs) are one of the most prevalent infections, afflicting 15 million women per year in the United States with annual healthcare costs exceeding $2-3 billion. Uropathogenic Escherichia coli (UPEC) are the main etiological agent of UTIs and employ numerous virulence factors for host colonization. The most common adhesive mechanism by which UPEC mediate host-pathogen interactions is the chaperone-usher pathway (CUP), which is responsible for the assembly of proteinaceous surface appendages termed pili. Generally, CUP pili function in adherence or invasion of host tissues and in biofilm formation on medical devices and body habitats. CUP pili are highly abundant and diverse among a wide variety of Gram-negative pathogens, with 38 distinct pilus types in Escherichia species alone, mediating a considerable range of biological tropisms through adhesins at the distal pilus tip. Typically, these adhesins have a lectin domain, which recognizes a specific carbohydrate receptor, and a pilin domain to anchor the adhesin to the pilus. This thesis specifically examines the structural, dynamic, and allosteric properties of distinct E. coli CUP pilus adhesins that govern interactions critical for pilus function at the host-pathogen interface during UTI. The type 1 pilus adhesin FimH is a critical virulence factor necessary for bacterial attachment to mannosylated receptors on the bladder epithelium during UTI. I determined through molecular and computational biophysics that FimH natively exists in a two-state conformational equilibrium in solution, composed of one low-affinity tense (T) and multiple high-affinity relaxed (R) conformations. I demonstrated that positively selected residues in FimH and ligand binding allosterically modulate this conformational equilibrium and that each of these conformational states engage mannose receptors through distinct binding modes. Mouse models of UTI indicate that FimH has evolved a ҭoderateӠmannose binding affinity through a balanced conformational equilibrium to optimize persistence in the bladder during UTI. Furthermore, I discovered novel small-molecule galactoside antagonists that inhibit the FimH-like adhesin FmlH from binding galactose-containing bladder and kidney epithelial receptors present during chronic UTI. Taken together, this thesis defines the biophysical basis of host receptor recognition and bacterial pathogenesis mediated by FimH and defines the atomic bases of distinct bacterial host tropisms mediated by FimH homologs, which were leveraged to spur the development of antibiotic-sparing, small-molecule glycomimetic antagonists as therapeutics for UTI and other infectious diseases