Effect of Intercalators on the Properties of Liquid-Crystalline Dispersions of Nucleic Acid–Chitosan Complex

Molecules of deoxyribonucleic acid and synthetic polydeoxyribonucleotides (NA) in the particles of liquid-crystalline dispersions resulting from interaction with chitosan are accessible to interaction with intercalators. The intercalation is accompanied by alteration in the direction of spatial twist of cholesterics of NA–chitosan complexes. This effect is absent in the case of classical cholesterics produced from NA molecules via phase exclusion, i.e., the cholesteric structure of NA–chitosan complex is very labile as distinct from classical cholesteric NA.     

Liquid-crystalline dispersions formed by the complexes of linear double-stranded DNA molecules with dendrimers

The specific features of liquid-crystalline dispersions formed by double-stranded DNA molecules interacting with polypropylenimine dendrimers of five generations (G1—G5) in aqueous saline solutions of various ionic strengths were studied. It was demonstrated that the binding of dendrimer molecules to DNA led to the formation of dispersions independently of solution ionic strength and dendrimer structure. By the example of a generation 4 dendrimer, it was shown that the shape of dispersion particles of the (DNA-dendrimer G4) complex were close to a sphere with a diameter of 300–400 nm. The boundary conditions (ionic strength of solution and molecular mass of dendrimer) for the formation of optically active (cholesteric) and optically inactive (DNA-dendrimer) dispersions were determined by circular dichroism spectroscopy. The dispersions formed by dendrimers G1–G3 and G5 were optically inactive. Dendrimers G4 formed liquid-crystalline dispersions of two types. Cholesteric liquid-crystalline dispersions were formed in high ionic strength solutions (μ > 0.4), whereas the dispersions formed in low and intermediate ionic strength solutions (μ < 0.4) lacked an intense negative band in their circular dichroism spectra. The effect of molecular crowding on both the (DNA-dendrimer G4) binding efficiency and the pattern of spatial packing of the (DNA-dendrimer G4) complexes in the liquid-crystalline dispersion particles was demonstrated. The factors determining the structural polymorphism of the liquid-crystalline dispersions of (DNA-dendrimer) complexes are postulated.     

Structural Insight Into hnRNP A2/B1 Homodimerization and DNA Recognition

Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) has been identified as a nuclear DNA sensor. Upon viral infection, hnRNP A2/B1 recognizes pathogen-derived DNA as a homodimer, which is a prerequisite for its translocation to the cytoplasm to activate the interferon response. However, the DNA binding mechanism inducing hnRNP A2/B1 homodimerization is unknown. Here, we show the crystal structure of the RNA recognition motif (RRM) of hnRNP A2/B1 in complex with a U-shaped ssDNA, which mediates the formation of a newly observed protein dimer. Our biochemical assays and mutagenesis studies confirm that the hnRNP A2/B1 homodimer forms in solution by binding to pre-generated ssDNA or dsDNA with a U-shaped bulge. These results depict a potential functional state of hnRNP A2/B1 in antiviral immunity and other cellular processes.