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AFM Meets Magnetic Tweezers to Probe Protein Dynamics under A Wide Range of Forces

Richter Nadia

Magnetic Tweezers (MT) is a single-molecule technology that
allows researchers to investigate the mechanical characteristics of
nucleic acids and protein-nucleic acid interactions in real time.
A MT system, contrary to its name, does not manage items in
the same way that a pair of macroscopic tweezers does. Because it
uses the magnetic field gradient generated by permanent
magnets to pull micrometer-size magnetic beads, the position of
which can be tracked in three dimensions using pictures given by
an inverted optical microscope and CMOS or CCD cameras, an
MT is truly a magnetic puller. Fixed beads are used to determine
the height of a glass surface as a zero-height reference (Refbead).
With a DNA molecule with proper functionalization at
their ends, DNA beads are anchored to the glass surface. The
distance between Reference- and DNA-beads is calculated using
the unique diffraction rings that arise from the optical image of
the beads. The DNA end-to-end distance as a function of time is
calculated by comparing the diffraction rings that arise from the
optical image of the beads with a calibration profile. As a result,
an MT setup can measure the extension of a DNA molecule in
real time at a given force, which is determined by the magnets'
distance from the beads.