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The bacterial fimbrial tip acts as a mechanical force sensor.

Aprikian P, Interlandi G, Kidd BA, Le Trong I, Tchesnokova V, Yakovenko O, Whitfield MJ, Bullitt E, Stenkamp RE, Thomas WE, Sokurenko EV - PLoS Biol. (2011)

Bottom Line: The conformation between the FimH pilin domain and the following FimG subunit of the tip is open and stable even when tensile force is applied, providing an extended lever arm for the hook unhinging under shear.Finally, the conformation between FimG and FimF subunits is highly flexible even in the absence of tensile force, conferring to the FimH adhesin an exploratory function and high binding rates.Comparison to other structures suggests that this property is common in unrelated bacterial and eukaryotic adhesive complexes that must function in dynamic conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, University of Washington, Seattle, Washington, United States of America.

ABSTRACT
There is increasing evidence that the catch bond mechanism, where binding becomes stronger under tensile force, is a common property among non-covalent interactions between biological molecules that are exposed to mechanical force in vivo. Here, by using the multi-protein tip complex of the mannose-binding type 1 fimbriae of Escherichia coli, we show how the entire quaternary structure of the adhesive organella is adapted to facilitate binding under mechanically dynamic conditions induced by flow. The fimbrial tip mediates shear-dependent adhesion of bacteria to uroepithelial cells and demonstrates force-enhanced interaction with mannose in single molecule force spectroscopy experiments. The mannose-binding, lectin domain of the apex-positioned adhesive protein FimH is docked to the anchoring pilin domain in a distinct hooked manner. The hooked conformation is highly stable in molecular dynamics simulations under no force conditions but permits an easy separation of the domains upon application of an external tensile force, allowing the lectin domain to switch from a low- to a high-affinity state. The conformation between the FimH pilin domain and the following FimG subunit of the tip is open and stable even when tensile force is applied, providing an extended lever arm for the hook unhinging under shear. Finally, the conformation between FimG and FimF subunits is highly flexible even in the absence of tensile force, conferring to the FimH adhesin an exploratory function and high binding rates. The fimbrial tip of type 1 Escherichia coli is optimized to have a dual functionality: flexible exploration and force sensing. Comparison to other structures suggests that this property is common in unrelated bacterial and eukaryotic adhesive complexes that must function in dynamic conditions.

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Shear-enhanced adhesion and catch bond behavior.(a) Binding of E. coli to uroepithelial cells at low (0.01 Pa) and high (0.1 Pa) shear stress in a flow chamber. (b) Level of E. coli binding under low (0.01 Pa) and high (0.1 Pa) shear stress to uroepithelial cells and mannose-BSA coated surface. (c) Binding of fimbrial tip-coated beads to mannose-BSA coated surface. (d) Binding of fimbrial tips to mannose-BSA in single molecule force spectroscopy experiments. The histograms in black (ordinate on the left, abscissa at the bottom) show the fraction of total pulls rupturing within a bin of a force range. The red line (ordinate on the right, abscissa at the top) displays the calculated unbinding rate (k_off) as a function of the force.
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pbio-1000617-g002: Shear-enhanced adhesion and catch bond behavior.(a) Binding of E. coli to uroepithelial cells at low (0.01 Pa) and high (0.1 Pa) shear stress in a flow chamber. (b) Level of E. coli binding under low (0.01 Pa) and high (0.1 Pa) shear stress to uroepithelial cells and mannose-BSA coated surface. (c) Binding of fimbrial tip-coated beads to mannose-BSA coated surface. (d) Binding of fimbrial tips to mannose-BSA in single molecule force spectroscopy experiments. The histograms in black (ordinate on the left, abscissa at the bottom) show the fraction of total pulls rupturing within a bin of a force range. The red line (ordinate on the right, abscissa at the top) displays the calculated unbinding rate (k_off) as a function of the force.

Mentions: The shear-dependent properties of the tip-incorporated FimH have been demonstrated previously using either yeast mannan, mannose coupled to bovine-serum-albumin (BSA), or guinea pig red blood cells [5],[7],[16],[17], all of which are surrogate receptors for the type 1 fimbriae [15]. We tested whether the type 1 fimbriae mediate shear-dependent adhesion to a natural target like bladder epithelial cells. Bacteria expressing type 1 fimbriae, with FimH, FimG, and FimF structurally identical to the ones in the crystallized tip complex, were used in parallel plate flow chamber experiments over the monolayer of bladder cell line T24. Bacterial adhesion to the cells increased more than 20-fold when shear was switched from 0.01 Pa to 0.1 Pa (Figure 2a,b). The pattern of E. coli adhesion to uroepthelial cells under different shears was similar to the bacterial binding to mannose-BSA coated on a surface (Figure 2b), indicating the monomannose specific mechanism of the shear-dependent E. coli adhesion to the bladder cells. Moreover, purified fimbrial tips that were used for the X-ray studies, when coupled to plastic beads, also mediated shear-enhanced binding to a mannose-BSA coated surface (Figure 2c).


The bacterial fimbrial tip acts as a mechanical force sensor.

Aprikian P, Interlandi G, Kidd BA, Le Trong I, Tchesnokova V, Yakovenko O, Whitfield MJ, Bullitt E, Stenkamp RE, Thomas WE, Sokurenko EV - PLoS Biol. (2011)

Shear-enhanced adhesion and catch bond behavior.(a) Binding of E. coli to uroepithelial cells at low (0.01 Pa) and high (0.1 Pa) shear stress in a flow chamber. (b) Level of E. coli binding under low (0.01 Pa) and high (0.1 Pa) shear stress to uroepithelial cells and mannose-BSA coated surface. (c) Binding of fimbrial tip-coated beads to mannose-BSA coated surface. (d) Binding of fimbrial tips to mannose-BSA in single molecule force spectroscopy experiments. The histograms in black (ordinate on the left, abscissa at the bottom) show the fraction of total pulls rupturing within a bin of a force range. The red line (ordinate on the right, abscissa at the top) displays the calculated unbinding rate (k_off) as a function of the force.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3091844&req=5

pbio-1000617-g002: Shear-enhanced adhesion and catch bond behavior.(a) Binding of E. coli to uroepithelial cells at low (0.01 Pa) and high (0.1 Pa) shear stress in a flow chamber. (b) Level of E. coli binding under low (0.01 Pa) and high (0.1 Pa) shear stress to uroepithelial cells and mannose-BSA coated surface. (c) Binding of fimbrial tip-coated beads to mannose-BSA coated surface. (d) Binding of fimbrial tips to mannose-BSA in single molecule force spectroscopy experiments. The histograms in black (ordinate on the left, abscissa at the bottom) show the fraction of total pulls rupturing within a bin of a force range. The red line (ordinate on the right, abscissa at the top) displays the calculated unbinding rate (k_off) as a function of the force.
Mentions: The shear-dependent properties of the tip-incorporated FimH have been demonstrated previously using either yeast mannan, mannose coupled to bovine-serum-albumin (BSA), or guinea pig red blood cells [5],[7],[16],[17], all of which are surrogate receptors for the type 1 fimbriae [15]. We tested whether the type 1 fimbriae mediate shear-dependent adhesion to a natural target like bladder epithelial cells. Bacteria expressing type 1 fimbriae, with FimH, FimG, and FimF structurally identical to the ones in the crystallized tip complex, were used in parallel plate flow chamber experiments over the monolayer of bladder cell line T24. Bacterial adhesion to the cells increased more than 20-fold when shear was switched from 0.01 Pa to 0.1 Pa (Figure 2a,b). The pattern of E. coli adhesion to uroepthelial cells under different shears was similar to the bacterial binding to mannose-BSA coated on a surface (Figure 2b), indicating the monomannose specific mechanism of the shear-dependent E. coli adhesion to the bladder cells. Moreover, purified fimbrial tips that were used for the X-ray studies, when coupled to plastic beads, also mediated shear-enhanced binding to a mannose-BSA coated surface (Figure 2c).

Bottom Line: The conformation between the FimH pilin domain and the following FimG subunit of the tip is open and stable even when tensile force is applied, providing an extended lever arm for the hook unhinging under shear.Finally, the conformation between FimG and FimF subunits is highly flexible even in the absence of tensile force, conferring to the FimH adhesin an exploratory function and high binding rates.Comparison to other structures suggests that this property is common in unrelated bacterial and eukaryotic adhesive complexes that must function in dynamic conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, University of Washington, Seattle, Washington, United States of America.

ABSTRACT
There is increasing evidence that the catch bond mechanism, where binding becomes stronger under tensile force, is a common property among non-covalent interactions between biological molecules that are exposed to mechanical force in vivo. Here, by using the multi-protein tip complex of the mannose-binding type 1 fimbriae of Escherichia coli, we show how the entire quaternary structure of the adhesive organella is adapted to facilitate binding under mechanically dynamic conditions induced by flow. The fimbrial tip mediates shear-dependent adhesion of bacteria to uroepithelial cells and demonstrates force-enhanced interaction with mannose in single molecule force spectroscopy experiments. The mannose-binding, lectin domain of the apex-positioned adhesive protein FimH is docked to the anchoring pilin domain in a distinct hooked manner. The hooked conformation is highly stable in molecular dynamics simulations under no force conditions but permits an easy separation of the domains upon application of an external tensile force, allowing the lectin domain to switch from a low- to a high-affinity state. The conformation between the FimH pilin domain and the following FimG subunit of the tip is open and stable even when tensile force is applied, providing an extended lever arm for the hook unhinging under shear. Finally, the conformation between FimG and FimF subunits is highly flexible even in the absence of tensile force, conferring to the FimH adhesin an exploratory function and high binding rates. The fimbrial tip of type 1 Escherichia coli is optimized to have a dual functionality: flexible exploration and force sensing. Comparison to other structures suggests that this property is common in unrelated bacterial and eukaryotic adhesive complexes that must function in dynamic conditions.

Show MeSH
Related in: MedlinePlus