Interaction-induced structural transformation of lysozyme and kappa-carrageenan in binary complexes

Water as a Structural Marker in Gelatin Hydrogels with Different Cross-Linking Nature

We have studied the molecular properties of water in physically and chemically cross-linked gelatin hydrogels by FTIR-spectroscopy, NMR relaxation, and diffusivity and broadband dielectric spectroscopy, which are sensitive to dynamical properties of water, being a structural marker of polymer network. All experiments demonstrated definite reinforcement of the hydrogel net structure and an increase in the amount of hydrate water. FTIR experiments have shown that the chemical cross-linking of gelatin molecules initiates an increase in the collagen-like triple helices "strength", as a result of infused restriction on protein molecular mobility. The "strengthening" of protein chains hinders the mobility of protein fragments, introducing complex modifications into the structural properties of water which are remained practically unchanged up to up to 30-40 °C.

Exploring the Origins of Association of Poly(acrylic acid) Polyelectrolyte with Lysozyme in Aqueous Environment through Molecular Simulations and Experiments

This study provides a detailed picture of how a protein (lysozyme) complexes with a poly(acrylic acid) polyelectrolyte (PAA) in water at the atomic level using a combination of all-atom molecular dynamics simulations and experiments. The effect of PAA and temperature on the protein's structure is explored. The simulations reveal that a lysozyme's structure is relatively stable except from local conformational changes induced by the presence of PAA and temperature increase. The effect of a specific thermal treatment on the complexation process is investigated, revealing both structural and energetic changes. Certain types of secondary structures (i.e., α-helix) are found to undergo a partially irreversible shift upon thermal treatment, which aligns qualitatively with experimental observations. This uncovers the origins of thermally induced aggregation of lysozyme with PAA and points to new PAA/lysozyme bonds that are formed and potentially enhance the stability in the complexes. As the temperature changes, distinct amino acids are found to exhibit the closest proximity to PAA, resulting into different PAA/lysozyme interactions; consequently, a different complexation pathway is followed. Energy calculations reveal the dominant role of electrostatic interactions. This detailed information can be useful for designing new biopolymer/protein materials and understanding protein function under immobilization of polyelectrolytes and upon mild denaturation processes.

Molecular insights into the phase transition of lysozyme into amyloid nanostructures: Implications of therapeutic strategies in diverse pathological conditions

Lysozyme, a well-known bacteriolytic enzyme, exhibits a fascinating yet complex behavior when it comes to protein aggregation. Under certain conditions, this enzyme undergoes flexible transformation, transitioning from partially unfolded intermediate units of native conformers into complex cross-β-rich nano fibrillar amyloid architectures. Formation of such lysozyme amyloids has been implicated in a multitude of pathological and medical severities, like hepatic dysfunction, hepatomegaly, splenic rupture as well as spleen dysfunction, nephropathy, sicca syndrome, renal dysfunction, renal amyloidosis, and systemic amyloidosis. In this comprehensive review, we have attempted to provide in-depth insights into the aggregating behavior of lysozyme across a spectrum of variables, including concentrations, temperatures, pH levels, and mutations. Our objective is to elucidate the underlying mechanisms that govern lysozyme's aggregation process and to unravel the complex interplay between its structural attributes. Moreover, this work has critically examined the latest advancements in the field, focusing specifically on novel strategies and systems, that have been implemented to delay or inhibit the lysozyme amyloidogenesis. Apart from this, we have tried to explore and advance our fundamental understanding of the complex processes involved in lysozyme aggregation. This will help the research community to lay a robust foundation for screening, designing, and formulating targeted anti-amyloid therapeutics offering improved treatment modalities and interventions not only for lysozyme-linked amyloidopathy but for a wide range of amyloid-related disorders.

Insights into the molecular mechanisms, structure-activity relationships and application prospects of polysaccharides by regulating Nrf2-mediated antioxidant response

The occurrence and development of many diseases are closely related to oxidative stress. In this context, accumulating evidence suggests that Nrf2, as the master switch of cellular antioxidant signaling, plays a central role in controlling the expression of antioxidant genes. The core molecular mechanism of polysaccharides treatment of oxidative stress-induced diseases is to activate Keap1/Nrf2/ARE signaling pathway, promote nuclear translocation of Nrf2, and up-regulate the expression of antioxidant enzymes. However, recent studies have shown that other signaling pathways in which polysaccharides exert antioxidant effects, such as PI3K/Akt/GSK3β, JNK/Nrf2 and NF-κB, have complex crosstalk with Keap1/Nrf2/ARE, may have direct effects on the nuclear translocation of Nrf2. This suggests a new strategy for designing polysaccharides as modulators of Nrf2-dependent pathways to target the antioxidant response. Therefore, in this work, we investigate the crosstalk between Keap1/Nrf2/ARE and other antioxidant signaling pathways of polysaccharides by regulating Nrf2-mediated antioxidant response. For the first time, the structural-activity relationship of polysaccharides, including molecular weight, monosaccharide composition, and glycosidic linkage, is systematically elucidated using principal component analysis and cluster analysis. This review also summarizes the application of antioxidant polysaccharides in food, animal production, cosmetics and biomaterials. The paper has significant reference value for screening antioxidant polysaccharides targeting Nrf2.

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.

Binding of ankaflavin with bovine serum albumin (BSA) in the presence of carrageenan and protective effects of Monascus yellow pigments against oxidative damage to BSA after forming a complex with carrageenan

Ankaflavin (AK) is a typical yellow pigment extracted from Monascus-fermented rice with several biological effects; however, its solubility is poor. Thus, research studies of the delivery systems of AK, especially those constructed from protein-polysaccharide complexes, have attracted considerable attention. However, the interactions that exist in the system have rarely been investigated. This work focused on the interactions between AK and bovine serum albumin (BSA) as well as the influence of carrageenan (Car) on the binding of AK to BSA. Results revealed that the quenching of BSA by AK involved the static quenching mechanism. The formed BSA-AK complexes were mainly maintained by hydrophobic forces and AK was located within the hydrophobic cavity of BSA. Compared to free AK or AK only complexed with BSA, a higher absorption intensity of AK was observed for the formed BSA-AK-Car complexes, indicating changes in the microenvironment of AK. This was confirmed by the increase in the α-helix content of BSA after the formation of BSA-AK-Car complexes. Hydrogen bond, van der Waals, and electrostatic interactions were verified to be the primary forces preserving the BSA-AK-Car complexes. Moreover, the antioxidant potential of Monascus-fermented products rich in AK (denoted as Mps), namely BSA-Mps and BSA-Mps-Car was evaluated. The antioxidant activity of Mps was negatively impacted by BSA, while the addition of Car could enhance the antioxidant capacity of BSA-Mps-Car complexes. Meanwhile, Mps showed a protective effect against free radical-induced oxidation damage to BSA, and Car could further improve this effect.

The Ability of Some Polysaccharides to Disaggregate Lysozyme Amyloid Fibrils and Renature the Protein

The deposition of proteins in the form of insoluble amyloid fibril aggregates is linked to a range of diseases. The supramolecular architecture of such deposits is governed by the propagation of β-strands in the direction of protofilament growth. In the present study, we analyze the structural changes of hen egg-white lysozyme fibrils upon their interactions with a range of polysaccharides, using AFM and FTIR spectroscopy. Linear anionic polysaccharides, such as κ-carrageenan and sodium alginate, are shown to be capable to disaggregate protofilaments with eventual protein renaturation. The results help to understand the mechanism of amyloid disaggregation and create a platform for both the development of new therapeutic agents for amyloidose treatment, and the design of novel functional protein-polysaccharide complex-based nanomaterials.

Regulation of Intersubunit Interactions in Homotetramer of Glyceraldehyde-3-Phosphate Dehydrogenases upon Its Immobilization in Protein-Kappa-Carrageenan Gels

Polysaccharides, being biocompatible and biodegradable polymers, are highly attractive as materials for protein delivery systems. However, protein-polysaccharide interactions may lead to protein structural transformation. In the current study, we analyze the structural adjustment of a homotetrameric protein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), upon its interactions with both flexible coil chain and the rigid helix of κ-carrageenan. FTIR spectroscopy was used to probe the secondary structures of both protein and polysaccharide. Electrostatically driven protein-polysaccharide interactions in dilute solutions resulted in an insoluble complex formation with a constant κ-carrageenan/GAPDH ratio of 0.2, which amounts to 75 disaccharide units per mole of protein tetramer. Upon interactions with both coiled and helical polysaccharides, a weakening of the intersubunit interactions was revealed and attributed to a partial GAPDH tetramer dissociation. In turn, protein distorted the helical conformation of κ-carrageenan when co-gelled. Molecular modeling showed the energy favorable interactions between κ-carrageenan and GAPDH at different levels of oligomerization. κ-Carrageenan binds in the region of the NAD-binding groove and the S-loop in OR contact, which may stabilize the OP dimers. The obtained results highlight the mutual conformational adjustment of oligomeric GAPDH and κ-carrageenan upon interaction and the stabilization of GAPDH's dissociated forms upon immobilization in polysaccharide gels.

Dimeric Lectin Chimeras as Novel Candidates for Gb3-Mediated Transcytotic Drug Delivery through Cellular Barriers

Receptor-mediated transcytosis is an elegant and promising strategy for drug delivery across biological barriers. Here, we describe a novel ligand-receptor pair based on a dimeric, engineered derivative of the Pseudomonas aeruginosa lectin LecA, here termed Di-LecA, and the host cell glycosphingolipid Gb3. We characterized the trafficking kinetics and transcytosis efficiencies in polarized Gb3-positive and -negative MDCK cells using mainly immunofluorescence in combination with confocal microscopy. To evaluate the delivery capacity of dimeric LecA chimeras, EGFP was chosen as a fluorescent model protein representing macromolecules, such as antibody fragments, and fused to either the N- or C-terminus of monomeric LecA using recombinant DNA technology. Both LecA/EGFP fusion proteins crossed cellular monolayers in vitro. Of note, the conjugate with EGFP at the N-terminus of LecA (EGFP-LecA) showed a higher release rate than the conjugate with EGFP at the C-terminus (LecA-EGFP). Based on molecular dynamics simulations and cross-linking studies of giant unilamellar vesicles, we speculate that EGFP-LecA tends to be a dimer while LecA-EGFP forms a tetramer. Overall, we confidently propose the dimeric LecA chimeras as transcytotic drug delivery tools through Gb3-positive cellular barriers for future in vivo tests.

κ-Carrageenan Hydrogel as a Matrix for Therapeutic Enzyme Immobilization

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.

Interaction-Induced Structural Transformations in Polysaccharide and Protein-Polysaccharide Gels as Functional Basis for Novel Soft-Matter: A Case of Carrageenans

Biocompatible, nontoxic, and biodegradable polysaccharides are considered as a promising base for bio-inspired materials, applicable as scaffolds in regenerative medicine, coatings in drug delivery systems, etc. The tunable macroscopic properties of gels should meet case-dependent requirements. The admixture of proteins to polysaccharides and their coupling in more sophisticated structures opens an avenue for gel property tuning via physical cross-linking of components and the modification of gel network structure. In this review recent success in the conformational studies of binary protein-polysaccharide gels is summarized with the main focus upon carrageenans. Future perspectives and challenges in rational design of novel polysaccharide-based materials are outlined.