Thermal denaturation of beta-lactoglobulin and stabilization mechanism by trehalose analyzed from Raman spectroscopy investigations

Unraveling the Nano-Bio Interface Interactions of a Lipase Adsorbed on Gold Nanoparticles under Laser Excitation

The complex nature and structure of biomolecules and nanoparticles and their interactions make it challenging to achieve a deeper understanding of the dynamics at the nano-bio interface of enzymes and plasmonic nanoparticles subjected to light excitation. In this study, circular dichroism (CD) and Raman spectroscopic experiments and molecular dynamics (MD) simulations were used to investigate the potential changes at the nano-bio interface upon plasmonic excitation. Our data showed that photothermal and thermal heating induced distinct changes in the secondary structure of a model nanobioconjugate composed of lipase fromCandida antarcticafraction B (CALB) and gold nanoparticles (AuNPs). The use of a green laser led to a substantial decrease in the α-helix content of the lipase from 66% to 13% and an increase in the β-sheet content from 5% to 31% compared to the initial conformation of the nanobioconjugate. In contrast, the differences under similar thermal heating conditions were only 55% and 11%, respectively. This study revealed important differences related to the enzyme secondary structure, enzyme-nanoparticle interactions, and the stability of the enzyme catalytic triad (Ser105-Asp187-His224), influenced by the instantaneous local temperature increase generated from photothermal heating compared to the slower rate of thermal heating of the bulk. These results provide valuable insights into the interactions between biomolecules and plasmonic nanoparticles induced by photothermal heating, advancing plasmonic biocatalysis and related fields.

From lab-based to in-line: Analytical tools for the characterization of whey protein denaturation and aggregation-A review

Whey protein denaturation and aggregation have long been areas of research interest to the dairy industry, having significant implications for process performance and final product functionality and quality. As such, a significant number of analytical techniques have been developed or adapted to assess and characterize levels of whey protein denaturation and aggregation, to either maximize processing efficiency or create products with enhanced functionality (both technological and biological). This review aims to collate and critique these approaches based on their analytical principles and outline their application for the assessment of denaturation and aggregation. This review also provides insights into recent developments in process analytical technologies relating to whey protein denaturation and aggregation, whereby some of the analytical methods have been adapted to enable measurements in-line. Developments in this area will enable more live, in-process data to be generated, which will subsequently allow more adaptive processing, enabling improved product quality and processing efficiency. Along with the applicability of these techniques for the assessment of whey protein denaturation and aggregation, limitations are also presented to help assess the suitability of each analytical technique for specific areas of interest.

Online Coupling of Size Exclusion Chromatography to Capillary Enhanced Raman Spectroscopy for the Analysis of Proteins and Biopharmaceutical Drug Products

The online coupling of size exclusion chromatography (SEC) to capillary enhanced Raman spectroscopy (CERS) based on a liquid core waveguide (LCW) flow cell was applied for the first time to assess the higher-order structure of different proteins. This setup allows recording of Raman spectra of the monomeric protein within complex mixtures, since SEC enables the separation of the monomeric protein from matrix components such as excipients of a biopharmaceutical product and higher molecular weight species (e.g., aggregates). The acquired Raman spectra were used for structural elucidation of well characterized proteins such as bovine serum albumin, hen egg white lysozyme, and β-lactoglobulin and of the monoclonal antibody rituximab in a medicinal product. Additionally, the CERS detection of the disaccharide sucrose, which is used as a stabilizing excipient, was quantified to achieve a limit of detection (LOD) of 120 μg and a limit of quantification (LOQ) of 363 μg injected on the column.

Application of Raman spectroscopy for the determination of proteins denaturation and amino acids decomposition temperature

Raman spectroscopy was employed to study the thermal denaturation of three different proteins, bovine serum albumin (BSA), lysozyme, ovalbumin; and the decomposition temperature of three amino acids, l-glutamine, l-cysteine, and l-alanine, all of them as lyophilized powders. All the Raman bands observed in the spectra obtained were recorded and analyzed at preset heating temperatures. The results obtained for either protein denaturation temperature T_D and amino acid decomposition temperatures T_M-dc, were compared with those measured by differential scanning calorimetry (DSC). The DSC and Raman results were additionally corroborated with a thermogravimetric analysis (TGA) for the case of proteins. This exercise indicated almost complete coincidence in the determination of these transition temperatures between the three techniques, evidencing the applicability of Raman spectroscopy in the study of denaturation and decomposition temperatures of proteins and amino acids.

The Loading of Epigallocatechin Gallate on Bovine Serum Albumin and Pullulan-Based Nanoparticles as Effective Antioxidant

Due to its poor stability and rapid metabolism, the biological activity and absorption of epigallocatechin gallate (EGCG) is limited. In this work, EGCG-loaded bovine serum albumin (BSA)/pullulan (PUL) nanoparticles (BPENs) were successfully fabricated via self-assembly. This assembly was driven by hydrogen bonding, which provided the desired EGCG loading efficiency, high stability, and a strong antioxidant capacity. The encapsulation efficiency of the BPENs was above 99.0%. BPENs have high antioxidant activity in vitro, and, in this study, their antioxidant capacity increased with an increase in the EGCG concentration. The in vitro release assays showed that the BPENs were released continuously over 6 h. The Fourier transform infrared spectra (FTIR) analysis indicated the presence of hydrogen bonding, hydrophobic interactions, and electrostatic interactions, which were the driving forces for the formation of the EGCG carrier nanoparticles. Furthermore, the transmission electron microscope (TEM) images demonstrated that the BSA/PUL-based nanoparticles (BPNs) and BPENs both exhibited regular spherical particles. In conclusion, BPENs are good delivery carriers for enhancing the stability and antioxidant activity of EGCG.

Whey protein films reinforced with bacterial cellulose nanowhiskers: Improving edible film properties via a circular economy approach

Edible films were developed using whey protein concentrate (WPC) and a natural bio-polymer, namely bacterial cellulose (BC). BC was produced via fermentation from orange peels and subsequently acid-hydrolyzed to obtain BC nanowhiskers (BCNW) with high crystallinity (XRD analysis). Morphology of BCNW was analyzed by SEM, TEM, and AFM. WPC/BCNW film composites, containing different amounts of BCNW (0.5-15%, w/w) were developed and characterized. WPC/BCNW film composite was analyzed by Raman spectroscopy, indicating the successful incorporation and the homogenous distribution of BCNW into the WPC film matrix. Mechanical characterization showed that BCNW behaved as a reinforcing filler in the WPC film, increasing tensile strength and Young's modulus by 32% and 80%, respectively. In addition, water vapor permeability was reduced by 33.9% upon the addition of 0.5% BCNW. This study presented a sustainable approach towards the production of WPC films with improved tensile and water barrier properties, suggesting its potential application as a packaging material.

Understanding the discrimination and quantification of monoclonal antibodies preparations using Raman spectroscopy

The use of Raman spectroscopy for analytical quality control of anticancer drug preparations in clinical pharmaceutical dispensing units is increasing in popularity, notably supported by commercially available, purpose designed instruments. Although not legislatively compulsory, analytical methods are frequently used post-preparation to verify the accuracy of a preparation in terms of identity and quantity of the drug in solution. However, while the rapid, cost effective and label free analysis achieved with Raman spectroscopy is appealing, it is important to understand the molecular origin of the spectral contributions collected from the solution of actives and excipients, to evaluate the strength and limitation for the technique, which can be used to identify and quantify either the prescribed commercial formulation, and/or the active drug itself, in personalised solutions. In the current study, four commercial formulations, Erbitux®, Truxima®, Ontruzant® and Avastin® of monoclonal antibodies (mAbs), corresponding respectively to cetuximab, rituximab, trastuzumab and bevacizumab have been used to highlight the key role of excipients in discrimination and quantification of the formulations. It is demonstrated that protein based anticancer drugs such as mAbs have a relatively weak Raman response, while excipients such as glycine, trehalose or histidine contribute significantly to the spectra. Multivariate analysis (partial least square regression and partial least square discriminant analysis) further demonstrates that the signatures of the mAbs themselves are not prominent in mathematical models and that those of the excipients are solely responsible for the differentiation of formulation and accurate determination of concentrations. While Raman spectroscopy can successfully validate the conformity of mAbs intravenous infusion solutions, the basis for the analysis should be considered, and special caution should be given to excipient compositions in commercial formulations to ensure reliability and reproducibility of the analysis.

Milk Processing Affects Structure, Bioavailability and Immunogenicity of β-lactoglobulin

Bovine milk is subjected to various processing steps to warrant constant quality and consumer safety. One of these steps is pasteurization, which involves the exposure of liquid milk to a high temperature for a limited amount of time. While such heating effectively ameliorates consumer safety concerns mediated by pathogenic bacteria, these conditions also have an impact on one of the main nutritional whey constituents of milk, the protein β-lactoglobulin. As a function of heating, β-lactoglobulin was shown to become increasingly prone to denaturation, aggregation, and lactose conjugation. This review discusses the implications of such heat-induced modifications on digestion and adsorption in the gastro-intestinal tract, and the responses these conformations elicit from the gastro-intestinal immune system.

Heat treatment of β-lactoglobulin affects its digestion and translocation in the upper digestive tract

Heat treatment is a commonly applied unit operation in the processing of β-lactoglobulin containing products. This does, however, influence its structure and thereby impacts its activity and digestibility. We describe how various heat-treatments of β-lactoglobulin change the digestibility using a modified version of the current consensus INFOGEST protocol. Additionally, protein was investigated for its translocation over the intestinal epithelial barrier, which would bring them in contact with immune cells. The extent of gastric digestibility was higher when the protein structure was more modified, while the influence of glycation with lactose was limited. Translocation studies of protein across Caco-2 cell monolayers showed a lower translocation rate of protein heated in solution compared to the others. Our study indicates that structural modifications after different heat-treatments of β-lactoglobulin increase in particular gastric digestibility and the translocation efficiency across intestinal epithelial cells.

Calcium Delivery System Assembled by a Nanostructured Peptide Derived from the Sea Cucumber Ovum

In this study, the binding mechanism, morphological, and conformational analysis of the complex of a sea cucumber ovum derived octapeptide (EDLAALEK) with Ca²⁺ as well as its calcium delivery behavior via the gastrointestinal (GI) tract were investigated. The Ca²⁺ specifically bound to two carboxyl oxygen atoms of C-terminal Glu and Asp on the EDLAALEK peptide at a stoichiometric ratio of 1:1. Calcium coordination induced the self-assembly of the EDLAALEK peptide, resulting in the formation of a nanocomposite with a crystal structure. Furthermore, the formed nanocomposite went through dissociation and self-assembly during in vitro GI digestion, accompanied by the release and rechelation of Ca²⁺, which was related to changes in their secondary structure. Nevertheless, the GI digests of the EDLAALEK-calcium complex could significantly enhance Ca²⁺ absorption across Caco-2 cell monolayers. The findings suggest that the sea cucumber ovum derived peptide has the potential as an efficient nanocarrier to transport calcium through the GI system.

A quercetin-based flavanoid (rutin) reverses amyloid fibrillation in β-lactoglobulin at pH 2.0 and 358 K

β-lactoglobulin (BLG) is a well characterized milk protein and a model for folding and aggregation studies. Rutin is a quercetin based-flavanoid and a famous dietary supplement. It is a potential protector from coronary heart disease, cancers, and inflammatory bowel disease. In this study, amyloid fibrillation is reported in BLG at pH 2.0 and temperature 358 K. It is inhibited to some extent by rutin with a rate of 99.3 h^-1 M^-1. Amyloid fibrillation started taking place after 10 h of incubation and completed near 40 h at a rate of 16.6 × 10^-3 h^-1, with a plateau during 40-108 h. Disruption of tertiary structure of BLG and increased solvent accessibility of hydrophobic core seem to trigger intermolecular assembly. Increase in 7% β-sheet structure at the cost of 10% α-helical structures and the electron micrograph of BLG fibrils at 108 h further support the formation of amyloid. Although it could not block amyloidosis completely, and even the time required to reach plateau remains the same, a decrease of growth rate from 16.6 × 10^-3 to 13.5 × 10^-3 h^-1 was observed in the presence of 30.0 μM rutin. Rutin seems to block solvent accessibility of the hydrophobic core of BLG. A decrease in the fibril population was observed in electron micrographs, with the increase in rutin concentration. All evidences indicate reversal of fibrillation in BLG in the presence of rutin.

Glycation of the Major Milk Allergen β-Lactoglobulin Changes Its Allergenicity by Alterations in Cellular Uptake and Degradation

SCOPE

During food processing, the Maillard reaction (МR) may occur, resulting in the formation of glycated proteins. Glycated proteins are of particular importance in food allergies because glycation may influence interactions with the immune system. This study compared native and extensively glycated milk allergen β-lactoglobulin (BLG), in their interactions with cells crucially involved in allergy.

METHODS AND RESULTS

BLG was glycated in MR and characterized. Native and glycated BLG were tested in experiments of epithelial transport, uptake and degradation by DCs, T-cell cytokine responses, and basophil cell degranulation using ELISA and flow cytometry. Glycation of BLG induced partial unfolding and reduced its intestinal epithelial transfer over a Caco-2 monolayer. Uptake of glycated BLG by bone marrow-derived dendritic cells (BMDC) was increased, although both BLG forms entered BMDC via the same mechanism, receptor-mediated endocytosis. Once inside the BMDC, glycated BLG was degraded faster, which might have led to observed lower cytokine production in BMDC/CD4+ T-cells coculture. Finally, glycated BLG was less efficient in induction of degranulation of BLG-specific IgE sensitized basophil cells.

CONCLUSIONS

This study suggests that glycation of BLG by MR significantly alters its fate in processes involved in immunogenicity and allergenicity, pointing out the importance of food processing in food allergy.

Electrostatic Interactions at N- and C-Termini Determine Fibril Polymorphism in Serum Amyloid A Fragments

Amyloid polymorphism presents a challenge to physical theories of amyloid formation and stability. The amyloidogenic protein serum amyloid A (SAA) exhibits complex and unexplained structural polymorphism in its N-terminal fragments: the N-terminal 11-residue peptide (SAA1-11) forms left-handed helical fibrils, while extension by one residue (SAA1-12) produces a rare right-handed amyloid. In this study, we use a combination of vibrational spectroscopy and ultramicroscopy to examine fibrils of these peptides and their terminally acetylated and amidated variants, in an effort to uncover the physical basis for this effect. Raman spectroscopy and atomic force microscopy provide evidence that SAA1-12 forms a β-helical fibril architecture, while SAA1-11 forms more typical stacked β-sheets. Importantly, N-terminal acetylation blocks fibril formation by SAA1-12 with no effect on SAA1-11, while C-terminal amidation has nearly the opposite effect. Together, these data suggest distinct electrostatic interactions at the N- and C-termini stabilize the two fibril structures; we propose model fibril structures in which C-terminal extension changes the favored intermolecular interaction between peptide monomers from an Arg1-C-terminus charge pair to an N-terminus-C-terminus charge pair. This model suggests a general mechanism for charge-mediated amyloid polymorphism and may inform strategies for design of peptide-based nanomaterials stabilized by engineered intermolecular contacts.

Recent developments in the Raman and infrared investigations of amorphous pharmaceuticals and protein formulations: A review

The success rate for drug discovery and the development of innovative therapeutic strategies are intimately related to the physical properties of the solid-state condensed matter, which have direct influence on the bioavailability of Active Pharmaceutical Ingredients. In order to transform a new molecule in efficient drug, the material is brought into an amorphous state using various manufacturing processes including freeze drying, spray drying, hot melt extrusion and loading in different delivery devices. The infrared and Raman spectroscopic analyses used for exploring disordered and amorphous states, for the monitoring of the drug physical stability in drug delivery systems are described in this review.

Exploring the heat-induced structural changes of β-lactoglobulin -linoleic acid complex by fluorescence spectroscopy and molecular modeling techniques

Linoleic acid (LA) is the precursor of bioactive oxidized linoleic acid metabolites and arachidonic acid, therefore is essential for human growth and plays an important role in good health in general. Because of the low water solubility and sensitivity to oxidation, new ways of LA delivery without compromising the sensory attributes of the enriched products are to be identified. The major whey protein, β-lactoglobulin (β-Lg), is a natural carrier for hydrophobic molecules. The thermal induced changes of the β-Lg-LA complex were investigated in the temperature range from 25 to 85 °C using fluorescence spectroscopy techniques in combination with molecular modeling study and the results were compared with those obtained for β-Lg. Experimental results indicated that, regardless of LA binding, the polypeptide chain rearrangements at temperatures higher than 75 °C lead to higher exposure of hydrophobic residues causing the increase of fluorescence intensity. Phase diagram indicated an all or none transition between two conformations. The LA surface involved in the interaction with β-Lg was about 497 Ǻ(2), indicating a good affinity between those two components even at high temperatures. Results obtained in this study provide important details about heat-induced changes in the conformation of β-Lg-LA complex. The thermal treatment at high temperature does not affect the LA binding and carrier functions of β-Lg.

Its preferential interactions with biopolymers account for diverse observed effects of trehalose

Biopolymer homeostasis underlies the health of organisms, and protective osmolytes have emerged as one strategy used by Nature to preserve biopolymer homeostasis. However, a great deal remains unknown about the mechanism of action of osmolytes. Trehalose, as a prominent example, stabilizes proteins against denaturation by extreme temperature and denaturants, preserves membrane integrity upon freezing or in dry conditions, inhibits polyQ-mediated protein aggregation, and suppresses the aggregation of denatured proteins. The underlying thermodynamic mechanisms of such diverse effects of trehalose remain unclear or controversial. In this study, we applied the surface-additive method developed in the Record laboratory to attack this issue. We characterized the key features of trehalose-biopolymer preferential interactions and found that trehalose has strong unfavorable interactions with aliphatic carbon and significant favorable interactions with amide/anionic oxygen. This dissection has allowed us to elucidate the diverse effects of trehalose and to identify the crucial functional group(s) responsible for its effects. With (semi)quantitative thermodynamic analysis, we discovered that 1) the unfavorable interaction of trehalose with hydrophobic surfaces is the dominant factor in its effect on protein stability, 2) the favorable interaction of trehalose with polar amides enables it to inhibit polyQ-mediated protein aggregation and the aggregation of denatured protein in general, and 3) the favorable interaction of trehalose with phosphate oxygens, together with its unfavorable interaction with aliphatic carbons, enables trehalose to preserve membrane integrity in aqueous solution. These results provide a basis for a full understanding of the role of trehalose in biopolymer homeostasis and the reason behind its evolutionary selection as an osmolyte, as well as for a better application of trehalose as a chemical chaperone.

Proteins in amorphous saccharide matrices: structural and dynamical insights on bioprotection

Bioprotection by sugars, and in particular trehalose peculiarity, is a relevant topic due to the implications in several fields. The underlying mechanisms are not yet clearly elucidated, and remain the focus of current investigations. Here we revisit data obtained at our lab on binary sugar/water and ternary protein/sugar/water systems, in wide ranges of water content and temperature, in the light of the current literature. The data here discussed come from complementary techniques (Infrared Spectroscopy, Molecular Dynamics simulations, Small Angle X-ray Scattering and Calorimetry), which provided a consistent description of the bioprotection by sugars from the atomistic to the macroscopic level. We present a picture, which suggests that protein bioprotection can be explained in terms of a strong coupling of the biomolecule surface to the matrix via extended hydrogen-bond networks, whose properties are defined by all components of the systems, and are strongly dependent on water content. Furthermore, the data show how carbohydrates having similar hydrogen-bonding capabilities exhibit different efficiency in preserving biostructures.

Raman spectroscopic characterization of structural changes in heated whey protein isolate upon soluble complex formation with pectin at near neutral pH

The mechanism leading to an alteration of heat aggregation of whey protein isolate (WPI) in the presence of pectin was investigated by assessing structural changes of proteins using Raman spectroscopy. WPI solutions were heated without or with pectin at 0.015-0.2 pectin to WPI weight ratios and pH 6.0-6.4. In the absence of pectin, thermal denaturation resulted in a loss of α-helical structure and an increase in β-structure and random coils of protein. At pH 6.0 and 6.2, heat aggregation of WPI was suppressed when pectin (0.05-0.15 pectin to WPI ratios) was present as shown by a decrease in turbidity and particle size. Concomitantly, changes in the secondary structures were reduced, indicating the enhanced stability of protein structure by pectin. Raman results also revealed that α-helix and β-sheet are dominant structures in heated WPI--pectin soluble complexes, and hydrogen bonding between biopolymers increased. The effect of pectin was pH dependent, indicating the involvement of electrostatic interaction.

β-Lactoglobulin as a molecular carrier of linoleate: characterization and effects on intestinal epithelial cells in vitro

The dairy protein β-lactoglobulin (βlg) is known to bind hydrophobic ligands such as fatty acids. In the present work, we investigated the biological activity in vitro of linoleate once complexed to bovine βlg. Binding of linoleate (C18:2) to bovine βlg was achieved by heating at 60 °C for 30 min at pH 7.4, resulting in a linoleate/βlg molar binding stoichiometry of 1.1, 2.1, and 3.4. Two types of binding sites were determined by ITC titrations. Binding of linoleate induced the formation of covalent dimers and trimers of βlg. The LD(50) on Caco-2 cells after 24 h was 58 μM linoleate. However, cell viability was unaffected when 200 μM linoleate was presented to the Caco-2 cells as part of the βlg complex. The Caco-2 cells did not increase mRNA transcript levels of long chain fatty acid transport genes, FATP4 and FABPpm, or increase levels of the cAMP signal, in response to the presence of 50 μM linoleate alone or as part of the βlg complex. Therefore, it is proposed that βlg can act as a molecular carrier and alter the bioaccessibility of linoleate/linoleic acid.