Low Molecular Weight Nucleoside Gelators: A Platform for Protein Aggregation Inhibition

Sulfated Polysaccharides as a Fighter with Protein Non-Physiological Aggregation: The Role of Polysaccharide Flexibility and Charge Density

Proteins can lose native functionality due to non-physiological aggregation. In this work, we have shown the power of sulfated polysaccharides as a natural assistant to restore damaged protein structures. Protein aggregates enriched by cross-β structures are a characteristic of amyloid fibrils related to different health disorders. Our recent studies demonstrated that model fibrils of hen egg white lysozyme (HEWL) can be disaggregated and renatured by some negatively charged polysaccharides. In the current work, using the same model protein system and FTIR spectroscopy, we studied the role of conformation and charge distribution along the polysaccharide chain in the protein secondary structure conversion. The effects of three carrageenans (κ, ι, and λ) possessing from one to three sulfate groups per disaccharide unit were shown to be different. κ-Carrageenan was able to fully eliminate cross-β structures and complete the renaturation process. ι-Carrageenan only initiated the formation of native-like β-structures in HEWL, retaining most of the cross-β structures. In contrast, λ-carrageenan even increased the content of amyloid cross-β structures. Furthermore, κ-carrageenan in rigid helical conformation loses its capability to restore protein native structures, largely increasing the amount of amyloid cross-β structures. Our findings create a platform for the design of novel natural chaperons to counteract protein unfolding.

Heterocycle-modified 2'-Deoxyguanosine Nucleolipid Analogs Stabilize Guanosine Gels and Self-assemble to Form Green Fluorescent Gels

Nucleoside-lipid conjugates are very useful supramolecular building blocks to construct self-assembled architectures suited for biomedical and material applications. Such nucleoside derivatives can be further synthetically manipulated to endow additional functionalities that could augment the assembling process and impart interesting properties. Here, we report the design, synthesis and self-assembling process of multifunctional supramolecular nucleolipid synthons containing an environment-sensitive fluorescent guanine. The amphiphilic synthons are composed of an 8-(2-(benzofuran-2-yl)vinyl)-guanine core and alkyl chains attached to 3'-O and 5'-O-positions of 2'-deoxyguanosine. The 2-(benzofuran-2-yl)vinyl (BFV) moiety attached at the C8 position of the nucleobase adopted a syn conformation about the glycosidic bond, which facilitated the self-assembly process through the formation of a G-tetrad as the basic unit. While 3',5'-diacylated BFV-modified dG analog stabilized the guanosine hydrogel by hampering the crystallization process and imparted fluorescence, BFV-modified dGs containing longer alkyl chains formed a green fluorescent organogel, which transformed into a yellow fluorescent gel in the presence of a complementary non-fluorescent cytidine nucleolipid. The ability of the dG analog containing short alkyl chains to modulate the mechanical property of a gel, and interesting fluorescence properties and self-assembling behavior exhibited by the dG analogs containing long alkyl chains in response to heat and complementary base underscore the potential use of these new supramolecular synthons in material applications.

Mechanistic investigations into the encapsulation and release of small molecules and proteins from a supramolecular nucleoside gel in vitro and in vivo

Supramolecular gels have recently emerged as promising biomaterials for the delivery of a wide range of bioactive molecules, from small hydrophobic drugs to large biomolecules such as proteins. Although it has been demonstrated that each encapsulated molecule has a different release profile from the hydrogel, so far diffusion and steric impediment have been identified as the only mechanisms for the release of molecules from supramolecular gels. Erosion of a supramolecular gel has not yet been reported to contribute to the release profiles of encapsulated molecules. Here, we use a novel nucleoside-based supramolecular gel as a drug delivery system for proteins with different properties and a hydrophobic dye and describe for the first time how these materials interact, encapsulate and eventually release bioactive molecules through an erosion-based process. Through fluorescence microscopy and spectroscopy as well as small angle X-ray scattering, we show that the encapsulated molecules directly interact with the hydrogel fibres - rather than being physically entrapped in the gel network. The ability of these materials to protect proteins against enzymatic degradation is also demonstrated here for the first time. In addition, the released proteins were proven to be functional in vitro. Real-time fluorescence microscopy together with macroscopic release studies confirm that erosion is the key release mechanism. In vivo, the gel completely degrades after two weeks and no signs of inflammation are detected, demonstrating its in vivo safety. By establishing the contribution of erosion as a key driving force behind the release of bioactive molecules from supramolecular gels, this work provides mechanistic insight into the way molecules with different properties are encapsulated and released from a nucleoside-based supramolecular gel and sets the basis for the design of more tailored supramolecular gels for drug delivery applications.