Differential Stability and Trade-Off Effects of Pathoadaptive Mutations in the Escherichia coli FimH Adhesin

Abstract

FimH is the tip adhesin of mannose-specific type 1 fimbriae of Escherichia coli, which are critical to the pathogenesis of urinary tract infections. Point FimH mutations increasing monomannose (1M)-specific uroepithelial adhesion are commonly found in uropathogenic strains of E. coli. Here, we demonstrate the emergence of a mixed population of clonally identical E. coli strains in the urine of a patient with acute cystitis, where half of the isolates carried a glycine-to-arginine substitution at position 66 of the mature FimH. The R66 mutation induced an unusually strong 1M-binding phenotype and a 20-fold advantage in mouse bladder colonization. However, E. coli strains carrying FimH-R66, but not the parental FimH-G66, had disappeared from the patient's rectal and urine samples collected from 29 to 44 days later, demonstrating within-host instability of the R66 mutation. No FimH variants with R66 were identified in a large (>600 strains) sequence database of fimH-positive E. coli strains. However, several strains carrying genes encoding FimH with either S66 or C66 mutations appeared to be relatively stable in the E. coli population. Relative to FimH-R66, the FimH-S66 and FimH-C66 variants mediated only moderate increases in 1M binding but preserved the ability to enhance binding under flow-induced shear conditions. In contrast, FimH-R66 completely lost shearenhanced binding properties, with bacterial adhesion being inhibited by shear forces and lacking a rolling mode of binding. These functional trade-offs may determine the natural populational instability of this mutation or other pathoadaptive FimH mutations that confer dramatic increases in 1M binding strength.Most Escherichia coli strains express type 1 fimbriae, hairlike adhesive organelles that mediate mannose-sensitive binding to host glycoproteins. The tip subunit, adhesin FimH, mediates shear-enhanced adhesion to monomannose (1M) receptors; the strength of binding is relatively weak under static conditions but is dramatically increased at high flow (21,22). Binding properties of FimH can be dramatically altered by single point mutations that occur throughout the protein and are responsible for up to 15-fold increases in the ability of E. coli strains to bind 1M under static conditions (4,14,15,17,18). Uropathogenic strains tend to bind 1M significantly better than strains of intestinal origin, and 1M binding is correlated with the ability to bind uroepithelial cells and with colonization of the urinary bladder in the mouse model of urinary tract infection (15). Thus, FimH mutations resulting in enhanced 1M binding are pathogenicity adaptive (pathoadaptive) in nature.Though FimH variants are 99% identical at the protein level, evolutionary analysis indicates that mutations occur in the adhesin more frequently than in even the structurally diverse major subunit of type 1 fimbriae, FimA (23). At the same time, mutations that enhance 1M binding do not persist in evolutionary terms due to the trade-off effects of pathoadaptive mutations (15). However, the na...

Genomic evidence of adaptive evolution in emergent Vibrio parahaemolyticus ecotypes

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Whole-genome comparison of urinary pathogenic Escherichia coli and faecal isolates of UTI patients and healthy controls

“…In the current study, with a large collection of clinical isolates, we observed only few signs of patho-adaptive mutations in the UTI isolates and no correlation of T6N with UTI. Previous studies have suggested that the FimH mutations A48V, A62S and G66R affect the binding affinity of FimH and N70S in combination with S78N has been correlated to UTI isolates without effect on the binding affinity (Aprikian et al, 2007; Chen et al, 2009; Schwartz et al, 2013; Sokurenko et al, 1995; Weissman et al, 2007). We identified N70S/S78N in FimH significantly more often in UTI isolates compared to faecal isolates.…”

Urinary tract infections: epidemiology, mechanisms of infection and treatment options

“…The two forms of the lectin domain have important implications for binding and pathogenesis: the elongated conformation binds mannose with a significantly higher affinity than the compact form 126 . Residues that control these conformational transitions have been shown to be under positive selection, and pathoadaptive alleles of FimH have subsequently been identified 126–128 . Thus, we now understand how protein–protein interactions and ligand binding can regulate a dynamic conformational equilibrium in the receptor-binding domain of FimH, and this is revealing unexpected insights into UTI pathogenesis and potentiating mannoside development.…”