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.

Gelatin, a water-soluble protein, shows unique gellification properties, which determine the active commercial availability of gelatin hydrogels in modern alimentary, cosmetic, and pharmaceutical applications. The traditional sources of gelatin for industrial technologies are pork and bovine skin and bones, which sometimes produce religious and some other restrictions. In recent years, there has been a significant increase in the production of gelatin from alternative sources, such as raw fish materials. Unfortunately, fish gelatin is characterized by weak gelling ability and a decrease in gelation and melting temperature, which are a consequence of the amino acid composition and structural features of fish gelatin. One of the ways to strengthen the natural gelling properties of fish gelatin is the structural modification of gelatin hydrogels by the introduction of polysaccharides of various natural origins. We have studied the association of our laboratory-made fish gelatin with three polysaccharides, namely, κ-carrageenan, alginate, and chitosan, which have distinct chemical structures and gelling capabilities. Structural features of the studied systems were analyzed by small-angle X-ray scattering (SAXS), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). We applied computer modeling of molecular interactions between fish gelatin and polysaccharides by means of molecular docking and molecular dynamics approaches. The existence of a correlation between the structure of gelatin-polysaccharide systems and their physicochemical properties was demonstrated by wetting angles (flow angles) and dynamic light scattering (DLS) studies of hydrodynamic sizes and surface ζ-potential.

During the last few decades, polysaccharide hydrogels attract more and more attention as therapeutic protein delivery systems due to their biocompatibility and the simplicity of the biodegradation of natural polymers. The protein retention by and release from the polysaccharide gel network is regulated by geometry and physical interactions of protein with the matrix. In the present work, we studied the molecular details of interactions between κ-carrageenan and three lipases, namely the lipases from Candida rugosa, Mucor javanicus, and Rhizomucor miehei—which differ in their size and net charge—upon protein immobilization in microparticles of polysaccharide gel. The kinetics of protein release revealed the different capability of κ-carrageenan to retain lipases, which are generally negatively charged; that was shown to be in line with the energy of interactions between polysaccharides and positively charged epitopes on the protein surface. These data create a platform for the novel design of nanocarriers for biomedical probes of enzymatic origin.