This work was supported by the European Union&#8217;s Horizon 2020 research and innovation programme under Grant Agreement No. 871124 Laserlab-Europe, by the Italian Ministry of University and Research (FIRB &#8220;Futuro in Ricerca&#8221; 2013 Grant No. RBFR13V4M2), and by Ente Cassa di Risparmio di Firenze. A.V. Kashchuk was supported by Human Frontier Science Program Cross-Disciplinary Fellowship LT008/2020-C.

1. Optical setup
NOTE: The experimental setup is composed of double optical tweezers with nanometer pointing stability and &#60; 1% laser intensity fluctuations. Under these conditions, stability of the dumbbell at the nanometer level is guaranteed under typical trap stiffness (0.1 pN/nm) and tension (1 pN - few tens of pN). Figure 2 shows a detailed scheme of the optical setup.
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S., Winkelmann, D. A., Capitanio, M., Ostap, E. M., Goldman, Y. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+molecule+mechanics+resolves+the+earliest+events+in+force+generation+by+cardiac+myosin.">Single molecule mechanics resolves the earliest events in force generation by cardiac myosin.</a> eLife. 8, 49266 (2019).</li><li>Clemen, A. E. -. M., Vilfan, M., Jaud, J., Zhang, J., B&#228;, M., Rief, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Force-dependent+stepping+kinetics+of+myosin-V.">Force-dependent stepping kinetics of myosin-V.</a> Biophysical Journal. 88, 4402-4410 (2005).</li><li>Howard, J., Hancock, W. 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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FIONA+in+the+trap:+The+advantages+of+combining+optical+tweezers+and+fluorescence.">FIONA in the trap: The advantages of combining optical tweezers and fluorescence.</a> Journal of Optics A: Pure and Applied Optics. 9 (8), 157 (2007).</li><li>Capitanio, M., Cicchi, R., Pavone, F. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Position+control+and+optical+manipulation+for+nanotechnology+applications.">Position control and optical manipulation for nanotechnology applications.</a> European Physical Journal B. 46 (1), 1-8 (2005).</li><li>Capitanio, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Optical Tweezers. An introduction to Single Molecule Biophysics. , (2017).</li><li>Capitanio, M., Cicchi, R., Saverio Pavone, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+and+time-shared+multiple+optical+tweezers+for+the+study+of+single+motor+proteins.">Continuous and time-shared multiple optical tweezers for the study of single motor proteins.</a> Optics and Lasers in Engineering. 45 (4), 450-457 (2007).</li><li>Gardini, L., Tempestini, A., Pavone, F. S., Capitanio, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-speed+optical+tweezers+for+the+study+of+single+molecular+motors.">High-speed optical tweezers for the study of single molecular motors.</a> Methods in Molecular Biology. 1805, (2018).</li><li>Capitanio, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calibration+of+optical+tweezers+with+differential+interference+contrast+signals.">Calibration of optical tweezers with differential interference contrast signals.</a> Review of Scientific Instruments. 73 (4), 1687 (2002).</li><li>Monico, C., Belcastro, G., Vanzi, F., Pavone, F. S., Capitanio, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combining+single-molecule+manipulation+and+imaging+for+the+study+of+protein-DNA+interactions.">Combining single-molecule manipulation and imaging for the study of protein-DNA interactions.</a> Journal of Visualized Experiments. (90), e51446 (2014).</li><li>Greenberg, M. J., Lin, T., Goldman, Y. E., Shuman, H., Ostap, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myosin+IC+generates+power+over+a+range+of+loads+via+a+new+tension-sensing+mechanism.">Myosin IC generates power over a range of loads via a new tension-sensing mechanism.</a> Proceedings of the National Academy of Sciences of the United States of America. 109 (37), 2433-2440 (2012).</li><li>Gardini, L., Arbore, C., Capitanio, M., Pavone, F. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+protocol+for+single+molecule+imaging+and+tracking+of+processive+myosin+motors.">A protocol for single molecule imaging and tracking of processive myosin motors.</a> MethodsX. 6, 1854-1862 (2019).</li><li>Ramaiya, A., Roy, B., Bugiel, M., Sch&#228;ffer, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinesin+rotates+unidirectionally+and+generates+torque+while+walking+on+microtubules.">Kinesin rotates unidirectionally and generates torque while walking on microtubules.</a> Proceedings of the National Academy of Sciences of the United States of America. 114 (41), 10894-10899 (2017).</li></ol>

The authors declare no competing interests.

Although single molecule techniques, such as the three-bead assay, are technically challenging and low throughput, UFFCS improves the detection of molecular interactions thanks to the high signal-to-noise ratio of the data. UFFCS allows the study of the load-dependence of motor proteins, with the main advantages of applying the force very rapidly upon binding of the motor to the filament to probe early and very rapid events in force production and weak binding states under controlled force; maintaining the force constant...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/62388">Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultra Force-Clamp Spectroscopy</a>. The title was updated.
The title was updated from:
Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultra Force-Clamp Spectroscopy
to:
Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy

An erratum was issued for:&#160;<a href="https://www.jove.com/t/62388">Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultra Force-Clamp Spectroscopy</a>. The title was updated.

Erratum: Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultra Force-Clamp Spectroscopy

In the last decades optical tweezers have been a valuable tool to elucidate the mechanochemistry of protein interactions at the single molecule level, due to the striking possibility of concurrent manipulation and measurement of conformational changes and enzymatic kinetics 1,2. In particular, the capability to apply and measure forces in the range of those exerted by molecular motors in the cell, together with the capacity to measure sub-nanometer conformational changes, made optical tweezers a unique single-molecule tool for unraveling the chemomechanical properties of motor proteins and their mechanical regulation.
Ultrafast force-clamp spectroscopy (UFFCS) is a single-molecule force-spectroscopy technique based on optical tweezers, developed to study the fast kinetics of molecular motors under load in a three-bead geometry (Figure 1a)3,4. UFFCS reduces the time lag for force application to the motor protein to the physical limit of optical tweezers, i.e., the mechanical relaxation time of the system, thus allowing the application of the force rapidly after the beginning of a myosin run (few tens of microseconds)3. This capability has been exploited to investigate the early mechanical events in fast skeletal 3 and cardiac5 muscle myosin to reveal the load dependence of the powerstroke, the weak- and strong-binding states, as well as the order of biochemical (Pi) and mechanical (powerstroke) events.
The three-bead geometry is usually employed to study non-processive motors, a single bead geometry with a force-clamp has been commonly used to investigate processive non-conventional myosins such as myosin Va6. However, there are several reasons to prefer a three-bead UFFCS assay also for processive myosins. First, the rapid application of load right after actin-myosin binding allows the measurement of the early events in force development as in non-processive motors. In addition, in the case of processive motors it also allows an accurate measurement of the motor&#39;s run lengths and run durations under constant force all through their progression (Figure 1b). Moreover, because of the high rate of the force feedback, the system can maintain the force constant during fast changes in position, such as the myosin working stroke, thereby guaranteeing a constant load during motor stepping. The high-temporal resolution of the system allows the detection of sub-ms interactions, opening the possibility of investigating weak binding of myosin to actin. Finally, the assay geometry guarantees that the force is applied along the actin filament, with negligible transverse and vertical components of the force. This point is of particular relevance since the vertical force component has been shown to influence significantly the load-dependence of motor&#39;s kinetics7,8. By using this technique, we could apply a range of assistive and resistive loads to processive myosin-5B and directly measure the load dependence of its processivity for a wide range of forces4.
As shown in Figure 1a, in this system a single actin filament is suspended between two polystyrene beads trapped in the focus of double optical tweezers (the &#34;dumbbell&#34;). An imbalanced net force F= F1-F2 is imposed on the filament, through a fast feedback system, which makes the filament move at constant velocity in one direction until it reaches a user-defined inversion point where the net force is reversed in the opposite direction. When the motor protein is not interacting with the filament, the dumbbell is free to move back and forth in a triangular wave shape (Figure 1b, bottom panel) spanning the pedestal bead on which a single motor protein is attached. Once the interaction is established the force carried by the dumbbell is very rapidly transferred to the motor protein and the motor starts displacing the filament by stepping under the force intensity and direction that was applied by the feedback system at the time of the interaction, until myosin detaches from actin. Being the displacement produced by the stepping of the motor dependent on the polarity of the trapped actin filament, according to the direction of the applied force the load can be either assistive, i.e., pushing in the same direction of the motor displacement (push in Figure 1b upper panel), or resistive, i.e., pulling in the opposite direction with respect to the motor displacement (pull in Figure 1b upper panel) making it possible to study the chemomechanical regulation of the motor processivity by both the intensity and the directionality of the applied load.
In the next sections all the steps to measure actin-myosin-5B interactions under different loads with an ultrafast force-clamp spectroscopy setup are fully described, including 1) the setting up of the optical setup, optical traps alignment and calibration procedures, 2) the preparations of all the components and their assembly in the sample chamber, 3) the measurement procedure, 4) representative data and data analysis to extract important physical parameters, such as the run length, the step size and the velocity of the motor protein.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>&#160;Aliphatic Amine Latex Beads</td>
			<td>ThermoFisher</td>
			<td>A37362</td>
			<td>1.0-&#956;m diameter, 2% (w/v)</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Sigma</td>
			<td>32201</td>
			<td></td>
		</tr>
		<tr>
			<td>Actin polymerization buffer</td>
			<td>Cytoskeleton</td>
			<td>BSA02</td>
			<td>10X</td>
		</tr>
		<tr>
			<td>AODs (acousto-optic deflectors)</td>
			<td>AA Opto Electronic</td>
			<td>DTS-XY 250</td>
			<td>Laser beam deflectors</td>
		</tr>
		<tr>
			<td>ATP</td>
			<td>Sigma</td>
			<td>A7699</td>
			<td></td>
		</tr>
		<tr>
			<td>Biotinylated-BSA</td>
			<td>ThermoFisher</td>
			<td>29130</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>Sigma</td>
			<td>B4287</td>
			<td></td>
		</tr>
		<tr>
			<td>Calmodulin from porcine brain (CaM)</td>
			<td>Merck Millipore</td>
			<td>208783</td>
			<td></td>
		</tr>
		<tr>
			<td>Catalase from bovine liver</td>
			<td>Sigma</td>
			<td>C40</td>
			<td></td>
		</tr>
		<tr>
			<td>Condenser</td>
			<td>Olympus</td>
			<td>OlympusU-AAC, Aplanat, Achromat</td>
			<td>NA 1.4, oil immersion</td>
		</tr>
		<tr>
			<td>Creatine phosphate disodium salt tetrahydrate</td>
			<td>Sigma</td>
			<td>27920</td>
			<td></td>
		</tr>
		<tr>
			<td>Creatine Phosphokinase from rabbit muscle</td>
			<td>Sigma</td>
			<td>C3755</td>
			<td></td>
		</tr>
		<tr>
			<td>DDs</td>
			<td>AA Opto Electronic</td>
			<td>AA.DDS.XX</td>
			<td>Two-channel digital synthesizer</td>
		</tr>
		<tr>
			<td>DL-Dithiothreitol (DTT)/td&#62;</td>
			<td>Sigma</td>
			<td>43819</td>
			<td></td>
		</tr>
		<tr>
			<td>EGTA</td>
			<td>Sigma</td>
			<td>E4378</td>
			<td></td>
		</tr>
		<tr>
			<td>G-actin protein</td>
			<td>Cytoskeleton</td>
			<td>AKL99</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma</td>
			<td>G7528</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose Oxidase from Aspergillus niger</td>
			<td>Sigma</td>
			<td>&#160;G7141</td>
			<td></td>
		</tr>
		<tr>
			<td>HaloTag succinimidyl ester O2 ligand</td>
			<td>Promega</td>
			<td>P1691</td>
			<td></td>
		</tr>
		<tr>
			<td>High vacuum silicone grease heavy</td>
			<td>Merck Millipore</td>
			<td>107921</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma</td>
			<td>P9541</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4/K2HPO4</td>
			<td>Sigma</td>
			<td>P5379/ P8281</td>
			<td></td>
		</tr>
		<tr>
			<td>Labview</td>
			<td>National Instruments</td>
			<td>version 8.1</td>
			<td>Data acquisition</td>
		</tr>
		<tr>
			<td>Labview FPGA module</td>
			<td>National Instruments</td>
			<td>version 8.1</td>
			<td>Fast Force-Clamp</td>
		</tr>
		<tr>
			<td>Matlab</td>
			<td>MathWorks</td>
			<td>2016</td>
			<td>Data analysis</td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Fluka</td>
			<td>63020</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope Objective</td>
			<td>Nikon</td>
			<td>Plan-Apo 60X</td>
			<td>NA 1.2, WD 0.2 mm, water imm.</td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Sigma</td>
			<td>M1254</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitrocellulose</td>
			<td>Sigma</td>
			<td>N8267</td>
			<td>0.45 pore size</td>
		</tr>
		<tr>
			<td>Pentyl acetate solution</td>
			<td>Sigma</td>
			<td>46022</td>
			<td></td>
		</tr>
		<tr>
			<td>Pure Ethanol</td>
			<td>&#160;Sigma</td>
			<td>2860</td>
			<td></td>
		</tr>
		<tr>
			<td>QPDs</td>
			<td>UDT</td>
			<td>DLS-20</td>
			<td>D Position Detecto</td>
		</tr>
		<tr>
			<td>Rhodamine BSA</td>
			<td>Molecular Probes</td>
			<td>A23016</td>
			<td></td>
		</tr>
		<tr>
			<td>Rhodamine Phalloidin</td>
			<td>&#160;Sigma</td>
			<td>P1951</td>
			<td></td>
		</tr>
		<tr>
			<td>Silica beads</td>
			<td>Bangslabs</td>
			<td>SS04N</td>
			<td>1.21 mm, 10% solids</td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>&#160;Sigma</td>
			<td>S2002</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptavidin protein</td>
			<td>&#160;Sigma</td>
			<td>189730</td>
			<td></td>
		</tr>
	</tbody>
</table>

dissecting mechanoenzymatic properties of processive myosins with ultrafast force-clamp spectroscopy

Ultrafast force-clamp spectroscopy (UFFCS) is a single molecule technique based on laser tweezers that allows the investigation of the chemomechanics of both conventional and unconventional myosins under load with unprecedented time resolution. In particular, the possibility to probe myosin motors under constant force right after the actin-myosin bond formation, together with the high rate of the force feedback (200 kHz), has shown UFFCS to be a valuable tool to study the load dependence of fast dynamics such as the myosin working stroke. Moreover, UFFCS enables the study of how processive and non-processive myosin-actin interactions are influenced by the intensity and direction of the applied force.
By following this protocol, it will be possible to perform ultrafast force-clamp experiments on processive myosin-5 motors and on a variety of unconventional myosins. By some adjustments, the protocol could also be easily extended to the study of other classes of processive motors such as kinesins and dyneins. The protocol includes all the necessary steps, from the setup of the experimental apparatus to sample preparation, calibration procedures, data acquisition and analysis.

Representative data consist in position records over time as shown in Figure 4. In the position record two kinds of displacement are visible. Firstly, when the myosin motor is not interacting with the actin filament the trapped beads are moving at constant velocity against the viscous drag force of the solution showing a linear displacement oscillating within the oscillation range set by the operator in a triangular wave3 (not visible in <strong class...

Watch this Scientific Journal Video about Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy at JoVE.com

Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy

Presented here is a comprehensive protocol to perform ultrafast force-clamp experiments on processive myosin-5 motors, which could be easily extended to the study of other classes of processive motors. The protocol details all the necessary steps, from the setup of the experimental apparatus to sample preparation, data acquisition and analysis.

Ultrafast force-clamp spectroscopy (UFFCS) is a single molecule technique based on laser tweezers that allows the investigation of the chemomechanics of ...

Ultrafast force-clamp spectroscopy is a single molecule technique based on laser tweezers that makes it possible to investigate the chemomechanics of myosins motors under load with the highest time resolution. This technique allows probing very rapid events in force production by maintaining the force constant during every phase of the motor interaction with full control on force directionality. By making appropriate adjustments, this protocol could be easily applied to other kinds of processive motors, including kinesins and dyneins, to uncover the regulation by force.After mounting one set of acousto-optic deflectors onto a linear translator, take an iris and adjust its aperture to fit the objective back aperture size. Replace the objective with the iris centered on the threaded objective housing. Move the translator toward the laser beam until the portion of the beam blocked by the piezo crystal is visible after the iris, and turn the translator slightly backward until the beam completely fills the iris aperture.To prepare silica beads in pentyl acetate, first dilute 20 microliters of 1.2 micron 10%solid silica beads in 1-1.5 milliliters of acetone with vortexing and 30 seconds of sonication. After sonicating, collect the beads by centrifugation and resuspend the bead pellet in 1 milliliter of fresh acetone for a second wash. After the second acetone wash, wash the beads three times in 1 milliliter of fresh pentyl acetate per wash under the same centrifugation conditions, and resuspend the pellet in 100 microliters of 1%of nitrocellulose and 900 microliters pentyl acetate.Next, use a pure ethanol-soaked piece of lab tissue to carefully wipe a 24 x 24 millimeter glass coverslip before using clean tweezers to rinse the glass directly in the ethanol and allowing the coverslip to dry under gentle nitrogen flow. Vortex and sonicate the prepared silica bead stock for 30 seconds and use an ethanol-cleaned 24 x 60 millimeter coverslip to smear 2 microliters of silica bead solution onto the surface of the smaller coverslip. While the beads are drying, clean a 26 x 76 millimeter slide as demonstrated, and place two 60-100 micron-thick lines of 3 millimeter double-sided taped onto the long edges of the slide.Using clean tweezers, place the bead-coated coverslip onto the tape with the beads facing the inside of the slide chamber, and fill the chamber with 15 millimolar phosphate buffer and floating polystyrene bead solution. Then, seal the chamber with silicon grease. To calibrate the pixel-to-nanometer ratio of the brightfield camera, acquire a first image of a silica bead on the coverslip surface approximately 5 microns from the center of the field of view.Move the stage to displace the bead 10 microns toward the center of the field of view and take a second image. Calculate the camera calibration constant by measuring the pixel distance between two positions of the bead. To calibrate the trap position, trap a single floating particle in one trap and move the acousto-optic deflectors in 0.2 megahertz steps, acquiring an image of the particle and the corresponding frequency of the deflectors for each step.Then, repeat the calibration for the second trap in the same manner. To calibrate the trap power and stiffness, trap a single particle in each trap and displace both traps using the acousto-optic deflectors in 0.2 megahertz steps, recording a Brownian motion of the particle in both traps with Quadrant Photodiode Detectors and the corresponding frequency of the acousto-optic deflectors. Obtain calibration constants by fitting a Lorentzian function to a power spectrum of the recorded Brownian motion.To assemble a sample for measurement, add 1 milligram per milliliter of biotinylated BSA to a new chamber with silica beads on the coverslip surface. After 5 minutes, wash the chamber with AB buffer and add 1 milligram per milliliter of streptavidin to the chamber. After 5 minutes, wash the chamber as demonstrated, and add 3 nanomolar biotinylated Myosin-5B heavy meromyosin in M5B buffer supplemented with 2 micromolar Calmodulin.After 5 minutes, wash the chamber three times with 1 milligram per milliliter of biotinylated BSA supplemented with 2 micromolar Calmodulin in AB buffer and wait 3 minutes after the final wash. Flow the reaction mixture and seal the chamber with silicon grease. To measure the sample, place the chamber onto the microscope stage and move the objective until the floating alpha-actinin beads are in focus.Switch on one trap and trap one bead. Once the first trap is occupied, move the translator to position the trapped bead close to the coverslip surface to avoid trapping multiple beads, and trap a bead in the second trap. Displace the sample through the long-range translators to locate actin filaments of at least 5 microns in length within the solution.When a filament has been spotted, move the sample to let a trapped bead approach one end of the filament. Once the filament has been attached, adjust the bead's distance to the approximate filament length and move the stage to create a flow in the unbound bead direction. The filament will become stretched by the flow and eventually bind to the second bead.The resulting complex is called a dumbbell"To establish actin-myosin contact, gently separate the two traps and set the filament to pretension levels up to about 3 piconewtons. To probe the rigidity of the dumbbell, make one trap oscillate in a triangular wave by changing the frequency of one acousto-optic deflector and verifying the consequent transmission of the motion to the trailing bead through its position signal. Move the stage to position the dumbbell in the proximity of a pedestal silica bead and adjust the height of the dumbbell so that the actin filament gets in contact with the silica bead surface.As observed in this representative position record, when the myosin motor is not interacting with the actin filament, the trapped beads move at a constant velocity against the viscous drag force of the solution. Once the myosin motor begins interacting with the filament, the force carried by the moving filament is very rapidly transferred to the protein, and the system velocity drops to zero, with the stepping events occurring under constant force till the end of the run. The force is switched from the positive to the negative direction by the feedback system, which switches the force direction when the bead reaches the edge of the oscillation range set by the user.When the myosin binds and displaces the filament toward the positive direction, it pushes the bead toward the upper edge of the oscillation range. If this happens under assistive force, the run of the myosin will be interrupted by the force direction inversion at the oscillation edge, limiting the length of the run to the amplitude of the dumbbell oscillation. Precise alignment of the optical system is necessary to achieve the optimal spatial and temporal resolution, while an accurate calibration is necessary to precisely determine the values of the applied forces.This technique has been adapted to study the sliding and targeted search of transcription factors in DNA as well as dynamic interactions between mechanotransduction proteins inducting over microtubule filaments.

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Research

JoVE Journal

Biology

1.2K visualizações.  National Institute of Optics, National Research Council. A espectroscopia de pinça de força ultrarrápida é uma técnica de molécula única baseada em pinças a laser que permite investigar a quimiomecânica de motores de miosinas sob carga com a maior resolução de tempo. Esta técnica permite sondar eventos muito rápidos na produção de força, mantendo a força constante durante todas as fases da interação motora com controle total sobre a direcionalidade da força. Ao fazer os ajustes apropriados, este protocolo poderia ser facilmente ...