Catch Bond-mediated Adhesion without a Shear Threshold: TRIMANNOSE VERSUS MONOMANNOSE INTERACTIONS WITH THE FimH ADHESIN OF ESCHERICHIA COLI

Lina M Nilsson,Wendy E Thomas,Elena Trintchina,Viola Vogel,Evgeni V Sokurenko

doi:10.1074/jbc.m511496200

Lina M Nilsson, Wendy E Thomas + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m511496200

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Abstract

The FimH protein is the adhesive subunit of Escherichia coli type 1 fimbriae. It mediates shear-dependent bacterial binding to monomannose (1M)-coated surfaces manifested by the existence of a shear threshold for binding, below which bacteria do not adhere. The 1M-specific shear-dependent binding of FimH is consistent with so-called catch bond interactions, whose lifetime is increased by tensile force. We show here that the oligosaccharide-specific interaction of FimH with another of its ligands, trimannose (3M), lacks a shear threshold for binding, since the number of bacteria binding under static conditions is higher than under any flow. However, similar to 1M, the binding strength of surface-interacting bacteria is enhanced by shear. Bacteria transition from rolling into firm stationary surface adhesion as the shear increases. The shear-enhanced bacterial binding on 3M is mediated by catch bond properties of the 1M-binding subsite within the extended oligosaccharide-binding pocket of FimH, since structural mutations in the putative force-responsive region and in the binding site affect 1M- and 3M-specific binding in an identical manner. A shear-dependent conversion of the adhesion mode is also exhibited by P-fimbriated E. coli adhering to digalactose surfaces.

Highlights

Bacterial adhesion, a critical initial step in colonization and biofilm formation, is commonly mediated by carbohydrate-binding lectin-like proteins expressed on the bacterial surface as part of hair-like fimbrial appendages or as nonfimbrial components [1,2,3,4]
Shear Stress Does Not Enhance Accumulation of E. coli on Surfaces Coated with a 3M Ligand—We tested the ability of bacteria that expressed a shear-enhanced 1M-binding FimH phenotype to adhere under flow conditions to surfaces coated with bovine RNase B, a model ligand containing N-linked high mannose type with terminally exposed 3M structures (3M-RB) [26]
In contrast to adhesion to 1M-BSA (Fig. 1A), shear stress did not cause any significant increase in accumulation of E. coli on surfaces coated with 3M-RB (Fig. 1B)

Summary

The abbreviations used are

1M, monomannose; 3M, trimannose; PBS, phosphate-buffered saline; BSA, bovine serum albumin; RB, RNase B; pN, piconewtons. ␣MM, methyl-␣-D-mannopyranoside. 1M, monomannose; 3M, trimannose; PBS, phosphate-buffered saline; BSA, bovine serum albumin; RB, RNase B; pN, piconewtons. We show here that the number of E. coli binding to 3M surfaces lacks a shear threshold (i.e. is both high and maximal at the lowest shear). The surface adhesion strength of individual bacteria on 3M was still enhanced by shear stress; at low shear, bacteria rolled along the surface, but as the shear was increased, the bacteria stopped and adhered firmly. We show here that, in analogy to FimH-1M, the lifetime of the FimH-3M complex can probably be switched by force from short to long lived. Shear-enhanced adhesion independent of FimH, but without a binding shear threshold, is demonstrated by E. coli expressing the P fimbrial adhesin PapG, a bacterial adhesin that binds to digalactose

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION