A method to track rotational motion for use in single-molecule biophysics

Area of Science:

• Biophysics
• Molecular Biology
• Nanotechnology

Background:

• DNA's double helix structure is fundamental to cellular processes like replication and repair, involving rotational motion and torsional strain.
• Magnetic tweezers (MTs) are powerful single-molecule tools for applying force and controlling rotation of nucleic acids, but lack direct rotational monitoring.
• Measuring torque is crucial for understanding DNA mechanics and protein-DNA interactions.

Purpose of the Study:

• To develop and validate a method for directly measuring rotational motion in magnetic tweezers experiments.
• To enable the extension of MTs into magnetic torque tweezers (MTTs) for direct torque measurement.
• To enhance the capabilities of single-molecule biophysical techniques.

Main Methods:

• Attaching non-magnetic beads as fiducial markers to magnetic beads for rotational tracking.
• Employing a specialized CCD image analysis algorithm to decouple translational and rotational motion.
• Utilizing kernel-based and correlation-based algorithms for precise bead position and rotation determination.

Main Results:

• Achieved a rotational resolution of 0.1° with translational resolution of 1-2 nm.
• Demonstrated the robustness of the tracking algorithm with simulated and experimental data.
• Showcased simultaneous multi-bead tracking capabilities and rotational fluctuation analysis of DNA tethers.

Conclusions:

• The developed rotation tracking method significantly enhances magnetic tweezers capabilities.
• This technique paves the way for direct torque measurements in single molecules using magnetic torque tweezers.
• The algorithm has broad applications in biophysics, including tethered particle motion and optical trapping.