Photochemical analysis of structural transitions in DNA liquid crystals reveals differences in spatial structure of DNA molecules organized in liquid crystalline form

Katarzyna Brach,Joanna Olesiak-Banska,Katarzyna Matczyszyn,Akiko Hatakeyama,Claude Nogues,Malcolm Buckle

doi:10.1038/s41598-018-22863-z

Abstract

The anisotropic shape of DNA molecules allows them to form lyotropic liquid crystals (LCs) at high concentrations. This liquid crystalline arrangement is also found in vivo (e.g., in bacteriophage capsids, bacteria or human sperm nuclei). However, the role of DNA liquid crystalline organization in living organisms still remains an open question. Here we show that in vitro, the DNA spatial structure is significantly changed in mesophases compared to non-organized DNA molecules. DNA LCs were prepared from pBluescript SK (pBSK) plasmid DNA and investigated by photochemical analysis of structural transitions (PhAST). We reveal significant differences in the probability of UV-induced pyrimidine dimer photoproduct formation at multiple loci on the DNA indicative of changes in major groove architecture.

Highlights

It has been shown that even very short DNA duplexes, which according to the Onsager hard rod model lack the anisotropic shape required for liquid crystal ordering, are able to organize into mesophases[1]
Homogenously spread DNA molecules were transported from the interior to the border of the drying drop and arranged perpendicular to the contact line; this led to liquid crystals (LCs) forming on the edge of the droplets[23,24,25]
Thick and visible by polarized light microscopy, a liquid crystalline phase layer was present in each sample that was used for further experiments

Summary

Introduction

It has been shown that even very short DNA duplexes, which according to the Onsager hard rod model lack the anisotropic shape required for liquid crystal ordering, are able to organize into mesophases[1]. In such mesophases, DNA chains align in parallel and because of end-to-end adhesion, form columnar aggregates. A characterisation of concentrated solutions of DNA and structural changes of DNA molecules in condensed phases in vitro is an important prerequisite for a better understanding of the complex biophysical phenomena of DNA condensation and its function in vivo. Polarized light microscopy was used to characterize liquid crystalline phases exposed to short times of UV irradiation

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