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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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Related in: MedlinePlus

Unhinging pathway of FimH under tensile force in MD simulations.(a) Location of the hinge axis (stereoview) determined with the program DynDom [61] by comparing the conformation of FimH at the end of the run pull 1 with its native conformation. (b) Sequence of rupture events of contacts between Ld and Pd versus distance from the hinge axis. A contact was defined as broken at the first time point when it ruptured and was not seen to reform within 300 ps. The Cα RMSD was calculated at the time of rupture (time averaged over 200 ps, Figures S3a, S4, S5a) in all six pulling runs and ranked according to a fractional ranking algorithm (where equal values receive the same raking as their respective ordinal rankings). The average and standard error of the mean of the ranked RMSD values are plotted against the distance of the respective contact from the hinge axis. The Cα RMSD from the native structure is a better measure of progress than the time of rupture itself, because rupture events are observed to occur in approximately the same order in every simulation but the time point when they occur varies across the simulations. The distance of a contact from the hinge axis is calculated as the distance of the geometric center of the involved side chains from the axis (in the case of hydrogen bonds, the geometric center of the D–H … A atoms is used). Significant inverse linear correlation (Pearson's ρ = 0.78; p value = 0.004) shows that the ranking number decreases with increasing distance, suggesting that the larger the distance from the hinge axis, the earlier the rupture of a contact.
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pbio-1000617-g005: Unhinging pathway of FimH under tensile force in MD simulations.(a) Location of the hinge axis (stereoview) determined with the program DynDom [61] by comparing the conformation of FimH at the end of the run pull 1 with its native conformation. (b) Sequence of rupture events of contacts between Ld and Pd versus distance from the hinge axis. A contact was defined as broken at the first time point when it ruptured and was not seen to reform within 300 ps. The Cα RMSD was calculated at the time of rupture (time averaged over 200 ps, Figures S3a, S4, S5a) in all six pulling runs and ranked according to a fractional ranking algorithm (where equal values receive the same raking as their respective ordinal rankings). The average and standard error of the mean of the ranked RMSD values are plotted against the distance of the respective contact from the hinge axis. The Cα RMSD from the native structure is a better measure of progress than the time of rupture itself, because rupture events are observed to occur in approximately the same order in every simulation but the time point when they occur varies across the simulations. The distance of a contact from the hinge axis is calculated as the distance of the geometric center of the involved side chains from the axis (in the case of hydrogen bonds, the geometric center of the D–H … A atoms is used). Significant inverse linear correlation (Pearson's ρ = 0.78; p value = 0.004) shows that the ranking number decreases with increasing distance, suggesting that the larger the distance from the hinge axis, the earlier the rupture of a contact.

Mentions: However, the most drastic changes occurred in the Ld-Pd structure, where the inter-domain hook straightened to an almost flat angle (Figure 4d and Figure S1e), with a large increase in the distance between the centers of mass of the domains, a significant decrease in buried surface area, and elimination of most native contacts (Figure 4 and Figures S3, S4, S5, S6, S7, S8, S9). In order to improve the statistical sampling of the events occurring during separation of the lectin from the pilin domain, three additional pulling simulations were performed with just the FimH protein. In both sets of pulling runs the rupture of inter-domain contacts between Ld and Pd happened in a sequential manner (Figure S10). Importantly, the combined results analysis indicates that the order of the contact breakage was inversely correlated with the contact's distance from the hinge axis, i.e., bonds further away from the hinge ruptured earlier in the simulations than contacts located closer to it (Figure 5). The Pearson's linear correlation coefficient was 0.78 with a p-value<0.01. This suggests that Pd and Ld unzip under tensile force, where only one or a few inter-domain contacts break at a time instead of most or all of the contacts breaking simultaneously. The fact that the sequence of breaking events is statistically correlated with the distance of the contacts from the hinge axis is indicative that the hooked shape of FimH allows a sequential unzipping of the stabilizing contacts as the hinge opens.


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)

Unhinging pathway of FimH under tensile force in MD simulations.(a) Location of the hinge axis (stereoview) determined with the program DynDom [61] by comparing the conformation of FimH at the end of the run pull 1 with its native conformation. (b) Sequence of rupture events of contacts between Ld and Pd versus distance from the hinge axis. A contact was defined as broken at the first time point when it ruptured and was not seen to reform within 300 ps. The Cα RMSD was calculated at the time of rupture (time averaged over 200 ps, Figures S3a, S4, S5a) in all six pulling runs and ranked according to a fractional ranking algorithm (where equal values receive the same raking as their respective ordinal rankings). The average and standard error of the mean of the ranked RMSD values are plotted against the distance of the respective contact from the hinge axis. The Cα RMSD from the native structure is a better measure of progress than the time of rupture itself, because rupture events are observed to occur in approximately the same order in every simulation but the time point when they occur varies across the simulations. The distance of a contact from the hinge axis is calculated as the distance of the geometric center of the involved side chains from the axis (in the case of hydrogen bonds, the geometric center of the D–H … A atoms is used). Significant inverse linear correlation (Pearson's ρ = 0.78; p value = 0.004) shows that the ranking number decreases with increasing distance, suggesting that the larger the distance from the hinge axis, the earlier the rupture of a contact.
© Copyright Policy
Related In: Results  -  Collection

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

pbio-1000617-g005: Unhinging pathway of FimH under tensile force in MD simulations.(a) Location of the hinge axis (stereoview) determined with the program DynDom [61] by comparing the conformation of FimH at the end of the run pull 1 with its native conformation. (b) Sequence of rupture events of contacts between Ld and Pd versus distance from the hinge axis. A contact was defined as broken at the first time point when it ruptured and was not seen to reform within 300 ps. The Cα RMSD was calculated at the time of rupture (time averaged over 200 ps, Figures S3a, S4, S5a) in all six pulling runs and ranked according to a fractional ranking algorithm (where equal values receive the same raking as their respective ordinal rankings). The average and standard error of the mean of the ranked RMSD values are plotted against the distance of the respective contact from the hinge axis. The Cα RMSD from the native structure is a better measure of progress than the time of rupture itself, because rupture events are observed to occur in approximately the same order in every simulation but the time point when they occur varies across the simulations. The distance of a contact from the hinge axis is calculated as the distance of the geometric center of the involved side chains from the axis (in the case of hydrogen bonds, the geometric center of the D–H … A atoms is used). Significant inverse linear correlation (Pearson's ρ = 0.78; p value = 0.004) shows that the ranking number decreases with increasing distance, suggesting that the larger the distance from the hinge axis, the earlier the rupture of a contact.
Mentions: However, the most drastic changes occurred in the Ld-Pd structure, where the inter-domain hook straightened to an almost flat angle (Figure 4d and Figure S1e), with a large increase in the distance between the centers of mass of the domains, a significant decrease in buried surface area, and elimination of most native contacts (Figure 4 and Figures S3, S4, S5, S6, S7, S8, S9). In order to improve the statistical sampling of the events occurring during separation of the lectin from the pilin domain, three additional pulling simulations were performed with just the FimH protein. In both sets of pulling runs the rupture of inter-domain contacts between Ld and Pd happened in a sequential manner (Figure S10). Importantly, the combined results analysis indicates that the order of the contact breakage was inversely correlated with the contact's distance from the hinge axis, i.e., bonds further away from the hinge ruptured earlier in the simulations than contacts located closer to it (Figure 5). The Pearson's linear correlation coefficient was 0.78 with a p-value<0.01. This suggests that Pd and Ld unzip under tensile force, where only one or a few inter-domain contacts break at a time instead of most or all of the contacts breaking simultaneously. The fact that the sequence of breaking events is statistically correlated with the distance of the contacts from the hinge axis is indicative that the hooked shape of FimH allows a sequential unzipping of the stabilizing contacts as the hinge opens.

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