| 1. |
- Andersson, Magnus, et al.
(författare)
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A structural basis for sustained bacterial adhesion : Biomechanical properties of CFA/I Pili
- 2012
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Ingår i: Journal of Molecular Biology. - : Elsevier. - 0022-2836 .- 1089-8638. ; 415:5, s. 918-928
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Tidskriftsartikel (refereegranskat)abstract
- Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal disease worldwide. Adhesion pili (or fimbriae), such as the CFA/I (colonization factor antigen I) organelles that enable ETEC to attach efficiently to the host intestinal tract epithelium, are critical virulence factors for initiation of infection. We characterized at single organelle level the intrinsic biomechanical properties and kinetics of individual CFA/I pili, demonstrating that weak external forces (7.5 pN) are sufficient to unwind the intact helical filament of this prototypical ETEC pilus and that it quickly regains its original structure when the force is removed. While the general relationship between exertion of force and an increase in the filament length for CFA/I pili associated with diarrheal disease is analogous to that of P-pili and type 1 pili, associated with urinary tract and other infections, the biomechanical properties of these different pili differ in key quantitative details. Unique features of CFA/I pili, including the significantly lower force required for unwinding, the higher extension speed at which the pili enter a dynamic range of unwinding, and the appearance of sudden force drops during unwinding can be attributed to morphological features of CFA/I pili including weak layer-to-layer interactions between subunits on adjacent turns of the helix, and the approximately horizontal orientation of pilin subunits with respect to the filament axis. Our results indicate that ETEC CFA/I pili are flexible organelles optimized to withstand harsh motion without breaking, resulting in continued attachment to the intestinal epithelium by the pathogenic bacteria that express these pili.
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| 2. |
- Andersson, Magnus, et al.
(författare)
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Differentiating pili expressed by enterotoxigenic and uropathogenic escherichia coli with optical tweezers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Enterotoxigenic Escherichia coli (ETEC) attach to the host epithelium in the intestinal tract via specific adhesion organelles expressed on the cell membrane. We investigate, by force measuring optical tweezers, the intrinsic biomechanical properties and kinetics of the colonization factor I (CFA/I) at a single pilus level. The measurements indicate that CFA/I pili are helix-like structures that can both be unraveled to a linearized polymer by applying a small external force, 7.5 ± 1.5 pN but also regain its helix-like structure when the applied force is reduced. The data confirm that layer-to-layer interactions, that stabilize the helix-like structure, are much weaker than the interactions found in pili expressed by Uropathogenic Escherichia coli (UPEC). It is also found, contrary to previous results assessed from UPEC pili, that the CFA/I undergo in some cases a sudden structural change, a force drop of ~2 pN, when unraveled from the helix-like configuration to an open helical linearized fiber. These data suggest a rotation of the filament about its helical axis, followed by a region in which the force required to extend the pili further increases rapidly. During this final elongation to a super-extended fiber, CFA/I pili do not show any structural transition as seen for UPEC pili. In addition, the CFA/I pili show faster kinetics than UPEC pili that allows for a larger dynamic regime of in vivo shear forces. The unfolding and refolding possibility points toward an organelle that has evolved to allow for dynamic damping of external forces and handling of harsh motion without breaking.
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| 3. |
- Baker, Joseph, et al.
(författare)
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Impact of an alpha helix and a cysteine-cysteine disulfide bond on the resistance of bacterial adhesion pili to stress
- 2021
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:21
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Tidskriftsartikel (refereegranskat)abstract
- Escherichia coli express adhesion pili that mediate attachment to host cell surfaces and are exposed to body fluids in the urinary and gastrointestinal tracts. Pilin subunits are organized into helical polymers, with a tip adhesin for specific host binding. Pili can elastically unwind when exposed to fluid flow forces, reducing the adhesin load, thereby facilitating sustained attachment. Here we investigate biophysical and structural differences of pili commonly expressed on bacteria that inhabit the urinary and intestinal tracts. Optical tweezers measurements reveal that Class 1a pili of uropathogenic E. coli (UPEC), as well as Class 1b of enterotoxigenic E. coli (ETEC), undergo an additional conformational change beyond pilus unwinding, providing significantly more elasticity to their structure than ETEC Class 5 pili. Examining structural and steered molecular dynamics simulation data, we find this difference in Class 1 pili subunit behavior originates from an alpha-helical motif that can unfold when exposed to force. A disulfide bond cross-linking beta-strands in Class 1 pili stabilizes subunits, allowing them to tolerate higher forces than Class 5 pili that lack this covalent bond. We suggest that these extra contributions to pilus resiliency are relevant for the UPEC niche since resident bacteria are exposed to stronger, more transient drag forces compared to those experienced by ETEC bacteria in the mucosa of the intestinal tract. Interestingly, Class 1b ETEC pili include the same structural features seen in UPEC pili, while requiring lower unwinding forces that are more similar to those of Class 5 ETEC pili.
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| 4. |
- Baker, Joseph, et al.
(författare)
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Unveiling the Contributions of Secondary Structure and Disulfide Bonds for Bacterial Adhesion Pili Extension using a Multiscale Approach
- 2021
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Bacterial adhesion pili are essential virulence factors for many pathogenic Escherichia coli, including bacteria that cause urinary tract infections (UPEC) and diarrheal diseases (ETEC). To sustain adhesion under forces similar to those in the fluid environments of the urinary tract and gastrointestinal tract, these pili (also called fimbriae) can extend to over seven times their original length. Both UPEC and ETEC can uncoil their quaternary structure under pulling force and re-coil to their helical form when the force is reduced, as observed using optical tweezers. However, after extension to a linear polymer UPEC undergo an additional reversible conformational change, that is not seen in ETEC. The mechanism for this conformational change in UPEC is not known. Therefore, to obtain a comprehensive picture of pilus extension we have taken a synergistic approach that combines optical tweezer experiments, structural data from cryo-EM, and steered molecular dynamics simulations to investigate the response of pilin subunits to force.Our multi-faceted approach provides novel molecular-scale insights into the structural changes that occur in UPEC and ETEC pili under pulling forces. We find that the conformational change observed in UPEC pili in optical tweezer experiments is correlated with the presence of an alpha helix. In addition, structural analysis and steered molecular dynamics simulations show that there is a disulfide bond that provides additional stability of UPEC pilin subunits that is not observed in ETEC pilins, which lack cysteine residues. Together, these results suggest that the mechanism of extension of bacterial adhesion pili is related to their environmental niche, and the magnitude of fluid forces in the urinary tract versus the GI tract.
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| 5. |
- Barbercheck Epler, Chelsea R., et al.
(författare)
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Bacterial adhesion pili
- 2018
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Ingår i: Membrane protein complexes. - Singapore : Springer Publishing Company. - 9789811077579 - 9789811077562 ; , s. 1-18
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Bokkapitel (refereegranskat)abstract
- Escherichia coli bacterial cells produce multiple types of adhesion pili that mediate cell-cell and cell-host attachments. These pili (also called 'fimbriae') are large biopolymers that are comprised of subunits assembled via a sophisticated micro-machinery into helix-like structures that are anchored in the bacterial outer membrane. They are commonly essential for initiation of disease and thus provide a potential target for antibacterial prevention and treatment. To develop new therapeutics for disease prevention and treatment we need to understand the molecular mechanisms and the direct role of adhesion pili during pathogenesis. These helix-like pilus structures possess fascinating and unique biomechanical properties that have been thoroughly investigated using high-resolution imaging techniques, force spectroscopy and fluid flow chambers. In this chapter, we first discuss the structure of pili and the micro-machinery responsible for the assembly process. Thereafter, we present methods for measurement of the biomechanics of adhesion pili, including optical tweezers. Data demonstrate unique biomechanical properties of pili that allow bacteria to sustain binding during in vivo fluid shear forces. We thereafter summarize the current biomechanical findings related to adhesion pili and show that pili biomechanical properties are niche-specific. That is, the data suggest that there is an organ-specific adaptation of pili that facilitates infection of the bacteria's target tissue. Thus, pilus biophysical properties are an important part of Escherichia coli pathogenesis, allowing bacteria to overcome hydrodynamic challenges in diverse environments.
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| 6. |
- Dahlberg, Tobias, 1990-, et al.
(författare)
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Unveiling molecular interactions that stabilize bacterial adhesion pili
- 2022
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Ingår i: Biophysical Journal. - : Biophysical Society. - 0006-3495 .- 1542-0086. ; 121:11, s. 2096-2106
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Tidskriftsartikel (refereegranskat)abstract
- Adhesion pili assembled by the chaperone-usher pathway are superelastic helical filaments on the surface of bacteria, optimized for attachment to target cells. Here, we investigate the biophysical function and structural interactions that stabilize P pili from uropathogenic bacteria. Using optical tweezers, we measure P pilus subunit-subunit interaction dynamics and show that pilus compliance is contour-length dependent. Atomic details of subunit-subunit interactions of pili under tension are shown using steered molecular dynamics (sMD) simulations. sMD results also indicate that the N-terminal “staple” region of P pili, which provides interactions with pilins that are four and five subunits away, significantly stabilizes the helical filament structure. These data are consistent with previous structural data, and suggest that more layer-to-layer interactions could compensate for the lack of a staple in type 1 pili. This study informs our understanding of essential structural and dynamic features of adhesion pili, supporting the hypothesis that the function of pili is critically dependent on their structure and biophysical properties.
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| 7. |
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| 8. |
- Doran, Matthew, et al.
(författare)
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CS20 bridge the gap between class 1 and class 5 bacterial adhesion pili
- 2022
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Ingår i: Biophysical Journal. - : Cell press. - 0006-3495 .- 1542-0086. ; 121:3, suppl. 1, s. 168a-168a
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Tidskriftsartikel (refereegranskat)abstract
- Enterotoxigenic Escherichia coli (ETEC) are pathogenic bacteria that cause diarrheal disease that disrupts the nutrition and the growth of children under the age of 5 and causes illness in travelers to countries where these bacteria are endemic. ETEC express long thin helical filaments on their surface, ∼1 micron long and 8 nm in diameter, called pili or fimbriae. Often essential virulence factors, these filaments, including ETEC CS20 pili, are composed of approximately 1,000 copies of the major pilin protein and one copy of a tip protein that provides binding specificity. While the structures of ETEC pili from different strains are similar, there are critical differences that alter their biophysical properties.ETEC express Class 1 and/or Class 5 pilins. The Class 1 CS20 pilin, CsbA, is genetically similar to FimA from Type 1 pili that are expressed on many strains of Escherichia coli, including bacteria that infect the urinary tract or the gastrointestinal tract, and also to PapA pilins expressed on bacteria that infect the kidneys. Thus, despite CS20 being expressed on ETEC, its pilin is genetically distant from the Class 5 CFA/I pilin, CfaB, the most commonly expressed ETEC pilin.We show here the three-dimensional structure and surface coulombic charge of CS20 pili, determined at 3.4 Å resolution by electron cryomicroscopy (cryo-EM). Our force spectroscopy data show that CS20 pili have a helix unwinding force that is twice that of CFA/I pili, and half that of Type 1 pili. Molecular dynamics simulations are further used to unveil features along the unwinding pathway at an atomistic scale. We see that CS20 pili bridge the genetic and environmental gap between Class 1 and Class 5 adhesion pili that are expressed on pathogenic bacteria.
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| 9. |
- Doran, Matthew H., et al.
(författare)
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Three structural solutions for bacterial adhesion pilus stability and superelasticity
- 2023
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Ingår i: Structure. - : Elsevier. - 0969-2126 .- 1878-4186.
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial adhesion pili are key virulence factors that mediate host-pathogen interactions in diverse epithelial environments. Deploying a multimodal approach, we probed the structural basis underpinning the biophysical properties of pili originating from enterotoxigenic (ETEC) and uropathogenic bacteria. Using cryo-electron microscopy we solved the structures of three vaccine target pili from ETEC bacteria, CFA/I, CS17, and CS20. Pairing these and previous pilus structures with force spectroscopy and steered molecular dynamics simulations, we find a strong correlation between subunit-subunit interaction energies and the force required for pilus unwinding, irrespective of genetic similarity. Pili integrate three structural solutions for stabilizing their assemblies: layer-to-layer interactions, N-terminal interactions to distant subunits, and extended loop interactions from adjacent subunits. Tuning of these structural solutions alters the biophysical properties of pili and promotes the superelastic behavior that is essential for sustained bacterial attachment.
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| 10. |
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