Biological Magnetometry: Torque on Superparamagnetic Beads in Magnetic Fields

Oene, Maarten M. van; Dickinson, Laura E.; Pedaci, Francesco; Köber, Mariana; Dulin, David; Lipfert, Jan; Dekker, Nynke H.

doi:10.1103/physrevlett.114.218301

Cited by 72 publications

(67 citation statements)

References 41 publications

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“…30 As a result, the attachment position of the DNA relative to the bottom of a bead will vary from bead to bead. Significant deviations from an attachment at the very bottom of the bead ( Figure S1 in the supplementary material) 41 result in biased measurements of DNA extension, 31 z .…”

Section: Assembly Of the Surface-dna-bead Systemmentioning

confidence: 99%

A force calibration standard for magnetic tweezers

Yu¹,

Dulin²,

Cnossen³

et al. 2014

Review of Scientific Instruments

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To study the behavior of biological macromolecules and enzymatic reactions under force, advances in single-molecule force spectroscopy have proven instrumental. Magnetic tweezers form one of the most powerful of these techniques, due to their overall simplicity, non-invasive character, potential for high throughput measurements, and large force range. Drawbacks of magnetic tweezers, however, are that accurate determination of the applied forces can be challenging for short biomolecules at high forces and very time-consuming for long tethers at low forces below ∼1 piconewton. Here, we address these drawbacks by presenting a calibration standard for magnetic tweezers consisting of measured forces for four magnet configurations. Each such configuration is calibrated for two commonly employed commercially available magnetic microspheres. We calculate forces in both time and spectral domains by analyzing bead fluctuations. The resulting calibration curves, validated through the use of different algorithms that yield close agreement in their determination of the applied forces, span a range from 100 piconewtons down to tens of femtonewtons. These generalized force calibrations will serve as a convenient resource for magnetic tweezers users and diminish variations between different experimental configurations or laboratories.

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Section: Assembly Of the Surface-dna-bead Systemmentioning

confidence: 99%

A force calibration standard for magnetic tweezers

Yu¹,

Dulin²,

Cnossen³

et al. 2014

Review of Scientific Instruments

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“…4C and F). We find τ 0 ( B ) by fixing the known magnetic parameters, namely the saturation magnetization M sat , the characteristic field B 0 , the anisotropy constant C , and the effective volume of superparamagnetic nanoparticles NV , to literature values2124. Then we fit Equation 3 to the data (black dashed lines in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Although the approximation has also been shown to qualitatively apply over full 2π rotation21, it has not been rigorously tested quantitatively. Therefore, we cannot exclude inaccuracies in the functional form of the model as a source of error in the fitted parameters.…”

Section: Resultsmentioning

confidence: 99%

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Applying torque to the Escherichia coli flagellar motor using magnetic tweezers

Oene

Dickinson

Cross

et al. 2017

Sci Rep

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The bacterial flagellar motor of Escherichia coli is a nanoscale rotary engine essential for bacterial propulsion. Studies on the power output of single motors rely on the measurement of motor torque and rotation under external load. Here, we investigate the use of magnetic tweezers, which in principle allow the application and active control of a calibrated load torque, to study single flagellar motors in Escherichia coli. We manipulate the external load on the motor by adjusting the magnetic field experienced by a magnetic bead linked to the motor, and we probe the motor’s response. A simple model describes the average motor speed over the entire range of applied fields. We extract the motor torque at stall and find it to be similar to the motor torque at drag-limited speed. In addition, use of the magnetic tweezers allows us to force motor rotation in both forward and backward directions. We monitor the motor’s performance before and after periods of forced rotation and observe no destructive effects on the motor. Our experiments show how magnetic tweezers can provide active and fast control of the external load while also exposing remaining challenges in calibration. Through their non-invasive character and straightforward parallelization, magnetic tweezers provide an attractive platform to study nanoscale rotary motors at the single-motor level.

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“…Both the BFM and the magnetic field exert a torque on the magnetic bead. For sufficiently large magnetic fields, the bead, and thus the motor, remain stalled in an equilibrium angular position, where the magnetic torque and the motor torque cancel (29). For a given bead size, the steady-state rotation of individual motors is measured under a negligible magnetic field for 50-300 s before manipulation.…”

Section: Resultsmentioning

confidence: 99%

A Catch-Bond Drives Stator Mechanosensitivity in the Bacterial Flagellar Motor

Nord

Gachon

Pérez-Carrasco

et al. 2018

Biophysical Journal

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The bacterial flagellar motor (BFM) is the rotary motor that rotates each bacterial flagellum, powering the swimming and swarming of many motile bacteria. The torque is provided by stator units, ion motive force-powered ion channels known to assemble and disassemble dynamically in the BFM. This turnover is mechanosensitive, with the number of engaged units dependent on the viscous load experienced by the motor through the flagellum. However, the molecular mechanism driving BFM mechanosensitivity is unknown. Here, we directly measure the kinetics of arrival and departure of the stator units in individual motors via analysis of high-resolution recordings of motor speed, while dynamically varying the load on the motor via external magnetic torque. The kinetic rates obtained, robust with respect to the details of the applied adsorption model, indicate that the lifetime of an assembled stator unit increases when a higher force is applied to its anchoring point in the cell wall. This provides strong evidence that a catch bond (a bond strengthened instead of weakened by force) drives mechanosensitivity of the flagellar motor complex. These results add the BFM to a short, but growing, list of systems demonstrating catch bonds, suggesting that this "molecular strategy" is a widespread mechanism to sense and respond to mechanical stress. We propose that force-enhanced stator adhesion allows the cell to adapt to a heterogeneous environmental viscosity and may ultimately play a role in surface-sensing during swarming and biofilm formation.bacterial flagellar motor | molecular motor | mechanosensitivity | catch bond | Escherichia coli T he bacterial flagellar motor (BFM) is a large molecular complex found in many species of motile bacteria which actively rotates each flagellum of the cell, enabling swimming, chemotaxis, and swarming (1, 2). The rotor of the BFM is embedded within and spans the cellular membranes, coupling rotation to the extracellular hook and flagellar filament. Multiple transmembrane complexes, called stator units, are anchored around the perimeter of the rotor and bound to the rigid peptidoglycan (PG) layer (3-5). By harnessing the ion motive force, the stator units are responsible for torque generation, acting upon the common ring formed by FliG proteins on the cytosolic side of the rotor (Fig. 1A) (6, 7).Several studies have revealed the continuous exchange of various BFM molecular constituents (8-10), demonstrating that a static model for the BFM structure is not adequate. A prime example, and in contrast to macroscopic rotary motors, the stator of the BFM is dynamic; while each bound stator unit acts upon the rotor independently (11, 12), their stoichiometry in the motor varies. Once anchored around the rotor, stator units dynamically turn over, eventually diffusing away in the inner membrane (10). Each additional recruited stator unit increases the total torque and thus the measured rotational speed of the motor (11, 13), and up to 11 units have been observed to engage in an individual motor in Esche...

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Biological Magnetometry: Torque on Superparamagnetic Beads in Magnetic Fields

Cited by 72 publications

References 41 publications

A force calibration standard for magnetic tweezers

A force calibration standard for magnetic tweezers

Applying torque to the Escherichia coli flagellar motor using magnetic tweezers

A Catch-Bond Drives Stator Mechanosensitivity in the Bacterial Flagellar Motor

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