| 1. |
- Castelain, Mickaël, et al.
(författare)
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Characterization of the Biomechanical Properties of T4 Pili Expressed by Streptococcus pneumoniae – A Comparison between Helix-like and Open Coil-like Pili
- 2009
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 10:9-10, s. 1533-1540
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial adhesion organelles, known as fimbria or pili, are expressed by Gram–positive as well as Gram–negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by Gram–positive Streptococcus pneumoniae with respect to their biomechanicalproperties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by Gram–negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble. Open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached bydistributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins.
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| 2. |
- Zakrisson, Johan, et al.
(författare)
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Helix-like bio-polymers can act as effective dampers for bacteria in flows
- 2012
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Ingår i: European Biophysics Journal. - Springer : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 41:6, s. 551-560
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Tidskriftsartikel (refereegranskat)abstract
- Biopolymers are vital structures for many liv- ing organisms; for a variety of bacteria, adhesion polymers play a crucial role for the initiation of colonization. Some bacteria express, on their surface, attachment organelles (pili) that comprise subunits formed into stiff helix-like structures that possess unique biomechanical properties. These helix-like structures possess a high degree of flexi- bility that gives the biopolymers a unique extendibility. This has been considered beneficial for piliated bacteria adhering to host surfaces in the presence of a fluid flow. We show in this work that helix-like pili have the ability to act as efficient dampers of force that can, for a limited time, lower the load on the force-mediating adhesin-receptor bond on the tip of an individual pilus. The model presented is applied to bacteria adhering with a single pilus of either of the two most common types expressed by uropathogenic Escherichia coli, P or type 1 pili, subjected to realistic flows. The results indicate that for moderate flows (~25 mm/s) the force experienced by the adhesin-receptor interaction at the tip of the pilus can be reduced by a factor of ~6 and ~4, respectively. The uncoiling ability pro- vides a bacterium with a ‘‘go with the flow’’ possibility that acts as a damping. It is surmised that this can be an important factor for the initial part of the adhesion process, in particular in turbulent flows, and thereby be of use for bacteria in their striving to survive a natural defense such as fluid rinsing actions.
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| 3. |
- Zakrisson, Johan, et al.
(författare)
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Rigid multibody simulation of a helix-like structure : the dynamics of bacterial adhesion pili
- 2015
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Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 44:5, s. 291-300
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Tidskriftsartikel (refereegranskat)abstract
- We present a coarse-grained rigid multibody model of a subunit assembled helix-like polymer, e.g., adhesion pili expressed by bacteria, that is capable of describing the polymer's force-extension response. With building blocks representing individual subunits, the model appropriately describes the complex behavior of pili expressed by the gram-negative uropathogenic Escherichia coli bacteria under the action of an external force. Numerical simulations show that the dynamics of the model, which include the effects of both unwinding and rewinding, are in good quantitative agreement with the characteristic force-extension response as observed experimentally for type 1 and P pili. By tuning the model, it is also possible to reproduce the force-extension response in the presence of anti-shaft antibodies, which dramatically changes the mechanical properties. Thus, the model and results in this work give enhanced understanding of how a pilus unwinds under the action of external forces and provide a new perspective of the complex bacterial adhesion processes.
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| 4. |
- Zakrisson, Johan, et al.
(författare)
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Tethered cells in fluid flows : beyond the Stokes’ drag force approach
- 2015
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Ingår i: Physical Biology. - : IOP Publishing. - 1478-3967 .- 1478-3975. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Simulations of tethered cells in viscous sub-layers are frequently performed using the Stokes' drag force, but without taking into account contributions from surface corrections, lift forces, buoyancy, the Basset force, the cells' finite inertia, or added mass. In this work, we investigate to what extent such contributions, under a variety of hydrodynamic conditions, influence the force at the anchor point of a tethered cell and the survival probability of a bacterium that is attached to a host by either a slip or a catch bond via a tether with a few different biomechanical properties. We show that a consequence of not including some of these contributions is that the force to which a bond is exposed can be significantly underestimated; in general by similar to 32-46%, where the influence of the surface corrections dominate ( the parallel and normal correction coefficients contribute similar to 5-8 or similar to 23-26%, respectively). The Basset force is a major contributor, up to 20%, for larger cells and shear rates. The lift force and inertia contribute when cells with radii >3 mu m have shear rates>2000 s(-1). Buoyancy contributes significantly for cells with radii > 3 mu m for shear rates<10 s(-1). Since the lifetime of a bond depends strongly on the force, both the level of approximation and the biomechanical model of the tether significantly affect the survival probability of tethered bacteria. For a cell attached by a FimH-mannose bond and an extendable tether with a shear rate of 3000 s(-1), neglecting the surface correction coefficients or the Basset force can imply that the survival probability is overestimated by more than an order of magnitude. This work thus shows that in order to quantitatively assess bacterial attachment forces and survival probabilities, both the fluid forces and the tether properties need to be modeled accurately.
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| 5. |
- Zakrisson, Johan, et al.
(författare)
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The shaft of the type 1 fimbriae regulates an externalforce to match the FimH catch bond
- 2013
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 104:10, s. 2137-2148
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Tidskriftsartikel (refereegranskat)abstract
- Type 1 fimbriae mediate adhesion of uropathogenic Escherichia coli to host cells. It has been hypothesized that due to their ability to uncoil under exposure to force, fimbriae can reduce fluid shear stress on the adhesin-receptor interaction by which the bacterium adheres to the surface. In this work, we develop a model that describes how the force on the adhesin-receptor interaction of a type 1 fimbria varies as a bacterium is affected by a time-dependent fluid flow mimicking in vivo conditions. The model combines in vivo hydrodynamic conditions with previously assessed biomechanical properties of the fimbriae. Numerical methods are used to solve for the motion and adhesion force under the presence of time-dependent fluid profiles. It is found that a bacterium tethered with a type 1 pilus will experience significantly reduced shear stress for moderate to high flow velocities and that the maximum stress the adhesin will experience is limited to ∼120 pN, which is sufficient to activate the conformational change of the FimH adhesin into its stronger state but also lower than the force required for breaking it under rapid loading. Our model thus supports the assumption that the type 1 fimbria shaft and the FimH adhesin-receptor interaction are optimized to each other, and that they give piliated bacteria significant advantages in rapidly changing fluidic environments.
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