Electrostatic zipper in curved DNA condensates
Amélie Leforestier (U. Paris-Saclay)
Joint seminar with LPS: beware of the unusual location
In helical polyelectrolytes like DNA, the electrostatic zipper is a model of interaction, which, taking into account the helical surface charge distribution, predicts mutual azimuthal orientation of close-packed molecules. This phenomenon is poorly documented experimentally. In particular, electrostatic zipper is not compatible with curvature, a general feature of dense states of DNA, both in vitro and in vivo. Using cryo-EM imaging of DNA toroids, we analyze the relationship between curvature, helical correlations, and DNA helical pitch. We show that in phase helical alignments are preferred over a wide range of ionic concentrations. Optimization of this preferred configuration is associated to rearrangements within the toroid as it grows, with establishment of the EZ followed by a global polygonal shaping. In addition, a local decrease in the DNA helical pitch is measured in highest curvature regions. This phenomenon, at work in DNA toroids, is also likely to occur in spheroidal globules, bacteriophage chromosomes, and, more generally, all forms of curved condensed DNA – and other helical polyelectrolytes – both in vivo and in vitro. In particular, it should be taken into account in material design involving curved DNA origami.