Molecular characterization of the β-lactoglobulin conjugated with fluorescein isothiocyanate: Binding sites and structure changes as function of pH

Aptamer-based sensitive fluorescence β-lactoglobulin food allergen bioassay via dual and cyclic bidirectional strand displacement amplifications

β-Lactoglobulin (β-Lg) is a prevalent allergenic protein found in most dairy products, which poses great food safety risks for individuals with allergies, especially for infants. Sensitive and effective detection methods for such allergens are essential to reduce the risk of allergies in daily life. Herein, a fluorescent aptamer bioassay based on a dual and cyclic bidirectional strand displacement means is developed for the sensitive detection of β-Lg in infant rice porridge and milk. The aptamer in the duplex DNA probe binds β-Lg to release the assistance strand to further hybridize with two hairpins, which triggers the initiation of two cyclic amplification cycles through the polymerization, displacement, and nicking of the strands under the action of DNA polymerase and endonuclease restriction enzymes. The amplification cycles lead to the unfolding of many fluorescently quenched signal probes to exhibit substantially enhanced fluorescence recovery for detecting β-Lg. The assay can realize detection of β-Lg in concentrations as low as 4.41 pM within the range of 0.01 to 10 nM. Furthermore, our sensing method has the capability to discriminate β-Lg from other proteins with high selectivity, resulting in low levels of β-Lg detection in rice porridge and milk samples, demonstrating promising potentials of the developed sensing method for monitoring various food allergens.

Conjugation of chitopentaose with β-lactoglobulin using Maillard reaction, and its effect on the allergic desensitization in vivo

The conjugation of chitopentaose (CHP) on β-lactoglobulin (βLg) via Maillard reaction was used to desensitize βLg. The stable βLg-CHP conjugate (βC-4) was formed at 4 h incubation, which contains 5 CHP attached molecules and a conjugated degree of 42 %. The conjugation promoted the thermal stability and emulsifying properties of βLg, and inhibited the immunoglobulin E (IgE) combining capacity by decreasing the content of β-sheet in βLg. Moreover, βLg-CHP conjugates were imparted with anti-oxidant properties and anti-inflammatory activities. Further, the combined action of inhibited IgE combining capacity and anti-inflammatory activities improved the allergy desensitization in βLg sensitized mice. The results showed that overexpressed IgE and inflammatory factors, unbalanced Th1-/Th2- immune cytokines were significantly attenuated after βLg was conjugated with CHP, avoiding the inflammatory lesions in spleen and colon. Additionally, the adverse changes in gut microbiota were alleviated in βC-4 group with a decrease of Bacteroidetes and increase of Firmicutes at phylum level and the probiotic bacteria of Lactobacillaceae was significantly improved at the family level. Thus, the conjugation of CHP can desensitize allergic reaction caused by βLg.

Microencapsulation of functional ovalbumin and bovine serum albumin with polylysine-alginate complex for sustained protein vehicle's development

Overcoming harsh gastric environment is still a challenging to bioactive proteins, microencapsulation provides one strategy in designing this protection barrier. In this work, bovine serum albumin and ovalbumin were chosen as model proteins, while polylysine-alginate complex was fabricated for microencapsulation purpose. Both of the protein-loaded microcapsules had regular internal microstructures. The model protein's embedding increased the thermal stability of the microcapsules. Both of the protein-loaded microcapsules had a slow release rate in simulated gastric fluids (pH 3.0), while a sustained release profile in simulated intestinal fluids (pH 6.4), indicating an excellent tolerance to the acidic gastric environment. The microencapsulation process was mild and had no influence on the protein's molecular weight, while a slight peak shifting occurred in the secondary structure of the released proteins. The developed microcapsules could be explored as a kind of vehicle for bioactive proteins applied in functional foods, health care products and medical formulations.

Probing the conjugation of epigallocatechin gallate with β-lactoglobulin and its in vivo desensitization efficiency

Epigallocatechin gallate (EGCG) and β-lactoglobulin (βLg) were conjugated by covalent bonds to form EGCG-βLg conjugates. This conjugation causes structural and bioactivity changes in βLg, which in turn can be used as a possible approach for desensitization to allergens. In this study, the desensitization mechanism was investigated by monitoring βLg secondary structure and immunoglobulin E (IgE) combining capacity changes on the basis of the conjugation mechanism. Furthermore, the desensitization efficiency in vivo was evaluated through animal experiments. The results show that temperature influenced the conjugation by decreasing the binding affinities (K_a) and binding numbers (n) of EGCG. The conjugation of EGCG decreased βLg's IgE combining capacity by decreasing the β-sheet component and imparted antioxidant properties by the introduction of hydroxyl groups. In addition, animal experiment results indicated that βLg induced significant changes in the levels of IgE and inflammatory cytokines, and the relative abundance of small intestinal flora, linked to the inflammatory lesions and anaphylaxis symptoms. EGCG-βLg conjugates can suppress the allergic response, attenuating serum IgE and relieving the anaphylaxis symptoms.

Probing protein dissociation from gold nanoparticles and the influence of temperature from the protein corona formation mechanism

Gold nanoparticles (AuNPs) provide a novel approach for protein enrichment and analysis due to their protein adsorption properties, forming a so called protein corona. This corona can significantly influence the protein's structure and characteristics, hindering their identification in situ. Dissociation is an important solution to analyze and identify the composition of protein coronas. However, a comprehensive picture of adsorbed protein dissociation is lacking. In this study, the protein dissociation from the protein corona and influencing factors were investigated on the basis of the formation mechanism and time evolution. Temperature and cysteine are the key factors influencing protein dissociation by altering the protein's binding ability. The results showed that half Au-S formation time is an important time point for thio-protein dissociation by the method of high speed centrifugation. When incubated for longer than that time, the thio-protein located in the hard corona could only be separated by β-mercaptoethanol replacement under analytical ultracentrifugation. However, Fourier-transform infrared spectroscopy (FTIR) revealed significant changes that occurred in βlg's secondary structure after ultracentrifugation. The Au-S bond formation time offers the potential to define the protein enrichment time of AuNPs.

Isolation and Self-Association Studies of Beta-Lactoglobulin

The aim of this study was to investigate isolated β-lactoglobulin (β-LG) from the whey protein isolate (WPI) solution using the column chromatography with SP Sephadex. The physicochemical characterization (self-association, the pH stability in various salt solutions, the identification of oligomeric forms) of the protein obtained have been carried out. The electrophoretically pure β-LG fraction was obtained at pH 4.8. The fraction was characterized by the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/TOF MS) technique. The use of the HCCA matrix indicated the presence of oligomeric β-LG forms, while the SA and DHB matrices enabled the differentiation of A and B isoforms in the sample. The impact of sodium chloride, potassium chloride, ammonium sulfate, and sodium citrate in dispersion medium on β-LG electrophoretic stability in solution was also studied. Type of the dispersion medium led to the changes in the isoelectric point of protein. Sodium citrate stabilizes protein in comparison to ammonium sulfate. Additionally, the potential of capillary electrophoresis (CE) with UV detection using bare fused capillary to monitor β-LG oligomerization was discussed. Obtained CE data were further compared by the asymmetric flow field flow fractionation coupled with the multi-angle light scattering detector (AF4-MALS). It was shown that the β-LG is a monomer at pH 3.0, dimer at pH 7.0. At pH 5.0 (near the isoelectric point), oligomers with structures from dimeric to octameric are formed. However, the appearance of the oligomers equilibrium is dependent on the concentration of protein. The higher quantity of protein leads to the formation of the octamer. The far UV circular dichroism (CD) spectra carried out at pH 3.0, 5.0, and 7.0 confirmed that β-sheet conformation is dominant at pH 3.0, 5.0, while at pH 7.0, this conformation is approximately in the same quantity as α-helix and random structures.

Probing gold nanoparticles for the desensitization to β-lactoglobulin from binding mechanism, structure and IgE binding changes

Because of the adsorption of proteins, gold nanoparticles (AuNPs) create potential biological risks in biomedicine, leading to the formation of the protein corona. This adsorption is mainly due to the formation of gold-sulfur (AuS) covalent bonds between the AuNPs and the -SH groups, causing bioactivity denaturation and biological problems; however, it could also lead to some biological benefits. We explored AuNPs as a potential material for desensitization to allergens, such as β-lactoglobulin (βLG). To address the desensitization of AuNPs, we investigated the binding mechanism and the specific relationship of the time evolution of AuS bond, secondary structure, and allergy changes. The formation of AuS bond takes approximately 9 h, consistent with the complete changes time in secondary structure and immunoglobulin E (IgE) combining capacity of the βLG, decreasing allergic reactions. These results indicate that AuNPs have the potential to minimize allergic reactions in the future.