Bundling of mRNA strands inside polyion complexes improves mRNA delivery efficiency in vitro and in vivo

RNA nanotechnology has promise for developing mRNA carriers with enhanced physicochemical and functional properties. However, the potential synergy for mRNA delivery of RNA nanotechnology in cooperation with established carrier systems remains unknown. This study proposes a combinational system of RNA nanotechnology and mRNA polyplexes, by focusing on mRNA steric structure inside the polyplexes. Firstly, several mRNA strands are bundled through hybridization with RNA oligonucleotide crosslinkers to obtain tight mRNA structure, and then the bundled mRNA is mixed with poly(ethylene glycol) (PEG)-polycation block copolymers to prepare PEG-coated polyplex micelles (PMs). mRNA bundling results in highly condensed mRNA packaging inside PM core with dense PEG chains on the surface, thereby, improving PM stability against polyion exchange reaction and ribonuclease (RNase) attack. Importantly, such stabilization effects are attributed to bundled structure of mRNA rather than the increase in total mRNA amount encapsulated in the PMs, as encapsulation of long mRNA strands without bundling fails to improve PM stability. Consequently, PMs loading bundled mRNA exhibit enhanced stability in mouse blood circulation, and induce efficient protein expression in cultured cells and mouse brain.

Raman-markers of X-ray radiation damage of proteins

Despite their high relevance, the mechanisms of X-ray radiation damage on protein structure yet have to be completely established. Here, we used Raman microspectrophotometry to follow X-ray-induced chemical modifications on the structure of the model protein bovine pancreatic ribonuclease (RNase A). The combination of dose-dependent Raman spectra and ultrahigh resolution (eight structures solved using data collected between 0.85 and 1.17 Å resolution on the same single crystal) allowed direct observation of several radiation damage events, including covalent bond breakages and formation of radicals. Our results are relevant for analytical photodamage detection and provide implications for a detailed understanding of the mechanisms of photoproduct formation.

The Kirkwood-Buff theory of solutions and the local composition of liquid mixtures

The present paper is devoted to the local composition of liquid mixtures calculated in the framework of the Kirkwood-Buff theory of solutions. A new method is suggested to calculate the excess (or deficit) number of various molecules around a selected (central) molecule in binary and multicomponent liquid mixtures in terms of measurable macroscopic thermodynamic quantities, such as the derivatives of the chemical potentials with respect to concentrations, the isothermal compressibility, and the partial molar volumes. This method accounts for an inaccessible volume due to the presence of a central molecule and is applied to binary and ternary mixtures. For the ideal binary mixture it is shown that because of the difference in the volumes of the pure components there is an excess (or deficit) number of different molecules around a central molecule. The excess (or deficit) becomes zero when the components of the ideal binary mixture have the same volume. The new method is also applied to methanol + water and 2-propanol + water mixtures. In the case of the 2-propanol + water mixture, the new method, in contrast to the other ones, indicates that clusters dominated by 2-propanol disappear at high alcohol mole fractions, in agreement with experimental observations. Finally, it is shown that the application of the new procedure to the ternary mixture water/protein/cosolvent at infinite dilution of the protein led to almost the same results as the methods involving a reference state.

Structuring Effects and Hydration Phenomena in Poly(Ethylene Glycol)/Water Mixtures Investigated by Brillouin Scattering

Aqueous solutions of poly(ethylene glycol) (PEG) of mean molecular mass of 600 g/mol (PEG600) are investigated by Brillouin scattering technique. At high PEG content, a relaxation phenomenon is observed, which is related to a local rearrangement of the polymer structure where the interaction, via hydrogen bonding, with the solvent molecules plays a role. The obtained values of the relaxation times match the literature data very well for a fast relaxation time revealed by dielectric relaxation measurements in very similar mixtures. The calculated concentration behaviors of the excess adiabatic compressibility turns out in good agreement with the previous findings from ultrasonic measurements at 3 MHz. The observed minimum in the adiabatic compressibility is interpreted as the result of the interaction between water and the EO units of the PEG chain, which results in a structure tighter then that typical of bulk water and of pure PEG600. Such a hypothesis is supported by the observation that volume fraction value of about 0.3 coincides with the concentration value at which full hydration of EO units takes place. The observation that at the same concentration, the polymer coils start to overlap each other further supports the idea that the adiabatic compressibility behavior is monitoring the structural evolution of the mixture. However, similar results are obtained for largely different binary mixture which suggests caution in taking this conclusion too literally. In particular, the hypothesis that the occurrence of an extreme in the excess adiabatic compressibility could be simply originated by statistical effects and that further work is required for disentangling entropic contribution from effects of hetero-association and self-aggregation of one or both the components.

Preferential hydration and solubility of proteins in aqueous solutions of polyethylene glycol

This paper is focused on the local composition around a protein molecule in aqueous mixtures containing polyethylene glycol (PEG) and the solubility of proteins in water+PEG mixed solvents. Experimental data from literature regarding the preferential binding parameter were used to calculate the excesses (or deficits) of water and PEG in the vicinity of beta-lactoglobulin, bovine serum albumin, lysozyme, chymotrypsinogen and ribonuclease A. It was concluded that the protein molecule is preferentially hydrated in all cases (for all proteins and PEGs investigated). The excesses of water and deficits of PEG in the vicinity of a protein molecule could be explained by a steric exclusion mechanism, i.e. the large difference in the sizes of water and PEG molecules. The solubility of different proteins in water+PEG mixed solvent was expressed in terms of the preferential binding parameter. The slope of the logarithm of protein (lysozyme, beta-lactoglobulin and bovine serum albumin) solubility versus the PEG concentration could be predicted on the basis of experimental data regarding the preferential binding parameter. For all the cases considered (various proteins, various PEGs molecular weights and various pHs), our theory predicted that PEG acts as a salting-out agent, conclusion in full agreement with experimental observations. The predicted slopes were compared with experimental values and while in some cases good agreement was found, in other cases the agreement was less satisfactory. Because the established equation is a rigorous thermodynamic one, the disagreement might occur because the experimental results used for the solubility and/or the preferential binding parameter do not correspond to thermodynamic equilibrium.