Chiral effects in dual-DNA braiding
D.J. Lee, R. Cortini, A.P. Korte, E.L. Starostin,
G.H.M. van der Heijden & A.A. Kornyshev
The biologically crucial problem of DNA braiding was studied in the past by
means of dual-DNA magnetic tweezer experiments. In such experiments, two DNA
molecules are braided about each other using an externally imposed force
and torque. Here we develop a theoretical model of molecular braiding that
includes interactions between molecules, thermal fluctuations, and the
elastic response of molecules, all in a consistent manner. This is useful to
study the chiral effects of helix-dependent electrostatic interactions on
the braid's equilibrium geometrical and mechanical properties. When
helix-dependent forces are weak, our model yields a reasonably accurate
reproduction of previously measured extension-rotation curves, where only
very slight chirality has been observed. On the other hand, when
helix-specific electrostatic forces are strong, the model predicts several
new features of the extension-rotation curves. These are: (a) a distinct
asymmetry between left-handed and right-handed DNA braiding; (b) the
emergence, under a critical pulling force, of coexistence regions of tightly
and loosely wound DNA; (c) spontaneous formation of left-handed DNA braids at
zero external torque (zero bead rotations). Strong chiral forces are expected
for braiding experiments conducted in solutions in which there are
counter-ions that bind specifically in the DNA grooves.
Soft Matter 9, 9833-9848 (2013)