Secondary Structure Of Ovalbumin Research Articles

Binding Interaction of Coumarin Derivative Daphnetin with Ovalbumin: Molecular Insights into the Complexation Process and Effects of Metal Ions and pH in the Binding and Antifibrillation Studies.

This study investigates the interaction between daphnetin and ovalbumin (OVA) as well as its potential to inhibit OVA fibrillation using both spectroscopic and computational analysis. A moderate binding affinity of 1 × 104 M-1 was observed between OVA and daphnetin, with a static quenched mechanism identified during the fluorescence quenching processes. Metal ions' (Cu2+ and Zn2+) presence led to an increase in the binding affinities of daphnetin toward OVA, mirroring a similar trend observed with the pH variation. Synchronous and 3D fluorescence studies indicated an increase in the polarity of the microenvironment surrounding the Trp residues during binding. Interestingly, circular dichroism and Fourier transform infrared studies showed a significant change in the secondary structure of OVA upon binding with daphnetin. The efficacy of daphnetin in inhibiting protein fibrillation was confirmed through thioflavin T and Congo Red binding assays along with fluorescence microscopic imaging analysis. The thermodynamic assessment showed positive ΔH° [+(29.34 ± 1.526) kJ mol-1] and ΔS° [+(181.726 ± 5.465) J mol-1] values, indicating the presence of the hydrophobic forces, while negative ΔG° signifies spontaneous binding interactions. These experimental findings were further correlated with computational analysis, revealing daphnetin dynamics within the binding site of OVA.

Effects of kappa-carrageenan on egg white ovalbumin for enhancing the gelation and rheological properties via electrostatic interactions

The protein-polysaccharide system is natural, and it has been widely applied in food manufacturing in recent years. However, the interactions in the system might be affected by numerous factors and this research investigated the effects of κ-carrageenan (κ-C) on the structure, interaction, and rheological characteristics of egg white ovalbumin (OVA) before and after heating. The zeta potential was adopted to show the surface charge of mixtures and its combination with turbidity test was used to discover the maximum associative interaction at the critical mixing ratio of κ-C: OVA. The results evidenced that the electrostatic interaction formed between OVA and κ-C. The critical ratio of OVA: κ-C (w/w) at 92:8 showed the minimum net charge (−0.5 ± 0.3 mV) and the maximum turbidity (0.122 ± 0.001 cm −1 ). All κ-C/OVA mixtures were observed shear thinning behaviour. The mixtures at 92:8 performed the highest apparent viscosity ( η ) and remained the maximum complex modulus ( G *) in the thermal cycle. The κ-C/OVA complex network was observed stronger than pure κ-C or OVA through the confocal scanning laser microscopy (CLSM). The rheological properties of the 92:8 mixtures supported the strongest electrostatic interactions between κ-C and OVA, corresponding to the largest aggregates structure in the CLSM images. A schematic model was further verified at the secondary structure of OVA using Fourier transform infrared (FTIR) spectroscopy. This study provides instructions to design innovative food systems that contain κ-C and OVA. • Ovalbumin (OVA) and κ-C were combined via electrostatic interaction. • κ-C induced the aggregates formation and the largest aggregates formed at 92:8. • The 92:8 mixtures showed the highest apparent viscosity ( η ). • The complex modulus ( G *) of 92:8 mixtures was the highest during thermal gelation. • The critical mixing ratio of OVA/κ-C mixtures occurred at 92:8.

Mechanistic understanding of the effects of ovalbumin-nanoliposome interactions on ovalbumin emulsifying properties

The effects of ovalbumin (OVA) and nanoliposome interactions on ovalbumin emulsifying properties were researched by UV–vis absorption, fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), particle size, Zeta-potential, surface hydrophobicity, contact angle (θ) and free sulfydryl (SH) content. Fluorescence analysis showed that the fluorescences of OVA were quenched after complexation with nanoliposomes. The secondary structure of OVA was slightly altered after the interactions. The peak shifts of C–H stretching vibration and O–H stretching vibration were observed in OVA-NL FTIR spectrum. It could be speculated that the hydrogen bonds and hydrophobic forces played a vital role in the interaction between OVA and NL. The interfacial tension of OVA was significantly decreased, and the surface hydrophobicity, θ and the content of free SH content of OVA increased in the presence of nanoliposomes. Furthermore, EAIs and ESIs of OVA increased from 32.55 to 64.79 m2/g, and from 30.23 to 95.48 min with the nanoliposome concentration increasing, respectively. These results showed that the vesicles could interact with OVA via non-covalent forces, and the emulsifying properties of OVA could be obviously improved after interaction with nanoliposomes. Our work provided a new insight into the application of OVA-NL in food industry.

PH influence on the mechanisms of interaction between chitosan and ovalbumin: a multi-spectroscopic approach

The forces behind supramolecular structures (SS) formation need to be deeply understood, to allow identifying conditions under which their production can be optimized. In this study, a multi-spectroscopic approach was used to study SS formation upon ovalbumin (OVA) and chitosan (CHS) interaction in HCl solution, at pH 4.0 (both biomacromolecules positively charged) or 6.0 (biomacromolecules oppositely charged). UV-Vis and fluorescence spectroscopies showed that the biomacromolecules interacted and formed complexes without suggesting major modifications in the protein’s structure. The increase in CHS concentration progressively augmented the UV-vis absorption of OVA-CHS structures at 278 nm, whereas reduced the fluorescence emission of OVA, at both pH values, without promoting obvious shift of the maximum fluorescence wavelength, with an estimated center of spectral mass of <λ> = 341.41 ± 0.31 nm (at pH 4.0) and <λ> = 342.30 ± 0.40nm (at pH 6.0). Additionally, a conjoint analysis of CD and FT-IR spectroscopies revealed that the presence of CHS promoted alterations on the secondary structure of OVA. Indeed, CHS may have affected the hydrogen bonding network that stabilized the structure in the native protein, increasing the stability of α-helix and random coil structures, which was reflected in the loss of β-sheet. Results suggested that the OVA-CHS interaction, at pH 6.0, are driven mainly by electrostatic forces (attractive) and H-bonds. At pH 4.0, these macromolecules are more likely to interact through a balance of electrostatic forces (repulsive), hydrophobic interactions and H-bonds.

Effects of single-mode microwave heating and dextran conjugation on the structure and functionality of ovalbumin–dextran conjugates

The proteins modified with carbohydrates through the glycation reaction are capable of changing and improving the functional properties of proteins. In this study, dextran was conjugated to ovalbumin (OVA) by traditional wet heating (WH) or single-mode microwave heating (MH) to improve the functional properties of OVA. Compared with traditional WH, MH for 15–60 min significantly increased the grafting degree (GD). The emulsifying activity and emulsion stability of the OVA–dextran conjugates improved under both traditional WH or MH (p < 0.05), especially under MH at 90 ℃ for 20 min. Correlation analysis showed that the emulsifying activity was positively correlated with surface hydrophobicity (p < 0.05), and emulsion stability was significantly positively correlated with surface hydrophobicity (p < 0.01) and positively correlated with the β-sheet contents (p < 0.05). Moreover, traditional WH and single-mode MH treatment could decrease tan δ, especially MH at 90 °C for 20 min. High GD and long MH treatment (≥25 min) resulted in a significant decrease in ⍺-helix and an increase in β-turn and γ-random coil. The secondary structure of OVA became loose, which was disadvantageous to the thermal stability of the OVA–dextran conjugates. In conclusion, compared with traditional WH, dextran conjugation with OVA via single-mode MH was an effective and safe way to improve the utilization value of OVA.

FTIR Analysis of Conformational Changes in the Secondary Structure of Ovalbumin: Effect of pH and Cosolvent Sugar-free Natura

a-helix, þ-sheet, þ-turns, and random coils are the three-dimensional local segments that constitute a protein secondary structure. Molecular vibrations of proteins are sensitive to structural organizations of peptide chains hence Fourier Transform infrared (FTIR) spectroscopy is one of the recognized techniques for the identification of protein secondary structures. However, the lower frequency region of FTIR especially the amide VI bands (in the region 590-490cm-1) is little studied for proteins. Further, the effect of sugar-free natura on ovalbumin stability is not yet studied to our knowledge. The present study examines the conformational changes in the secondary structure of ovalbumin (OVA) protein under the influence of pH variations (2, 5, 7, 9, and 12) and also cosolvent sugar-free Natura (SFN) inclusion. From the primary absorption spectra of the amide VI bands, the second derivative analysis is furnished to quantify the secondary structural elements of protein thereby conformational changes are analyzed. From obtained results, it is found that conformational changes occur between two major secondary structures of a-helix and þ-sheet of OVA due to variation of pH and inclusion of cosolvent. Also, the results confirm that the denaturation of OVA in the presence of SFN irrespective of pH.

Study on structural, rheological and foaming properties of ovalbumin by ultrasound-assisted glycation with xylose.

This study was to evaluate the effect of ultrasound-assisted glycation with xylose on the foaming properties, physicochemical and structural characteristics of ovalbumin (OVA). The number of free amino groups in the glycated OVA (sOVA-X) significantly decreased with the increase of treatment time. The results obtained by circular dichroism (CD) and spectrofluorimetric measurements showed that there were slight changes on the subunits and secondary structure of OVA, indicating that the tertiary structure became more flexible and loose after the sonicated glycation treatment. The glycated OVA had higher solubility and foaming properties than the untreated samples. Therefore, ultrasound improved the glycation extent, and the changes in molecular structure were responsible for their different foaming ability and foaming stability. Our study also provided principle knowledge to understand how the viscosity and rheology were related to the foaming properties of OVA glycation by xylose. The results indicated that ultrasound-assisted glycation could be an excellent approach to improve the functional properties of OVA and promote its application in food industry.

Molecular interaction of cyanidin-3-O-glucoside with ovalbumin: insights from spectroscopic, molecular docking and in vitro digestive studies

Anthocyanins bound with proteins have influence on the digestibility of proteins. In this study, the interaction between cyanidin-3-O-glucoside (C3G) and ovalbumin (OVA) was investigated through multi-spectroscopy and molecular docking. The interactive effect of C3G on OVA digestibility was estimated by an in vitro digestion model. Fluorescence studies indicated that C3G quenched the fluorescence of OVA in a static mode, where the binding constants (Ka) at 298, 308 and 318 K were above 105 M–1, indicating a strong binding affinity of C3G with OVA. The negative values of thermodynamic parameters (ΔG, ΔH and ΔS) revealed a spontaneous binding process, where hydrogen and van der Waals forces were involved in stabilizing the OVA-C3G complex. The secondary structure of OVA was modified by C3G binding, with augmented β-sheet (21.5%–25.1%) and diminished α-helix (23.3%–21.6%). Besides, C3G substantially inhibited the digestion of OVA in pancreatin solution whereas it had negligible effect on pepsin. Furthermore, molecular docking and cleavage site prediction studies showed that the hydrogen binding sites of C3G are not near to the cleavage sites of pepsin but partially overlap trypsin cleavages sites in OVA, which might lead to an inhibited effect on pancreatic digestion. These results provide a better understanding of the anthocyanin-protein interactions and their effect on the protein digestibility.Communicated by Ramaswamy H. Sarma

Improved antioxidant activity and physicochemical properties of curcumin by adding ovalbumin and its structural characterization

Protein as a carrier to improve the solubility and bioavailability of curcumin has been studied widely. However, to date the researches were mainly focused on its binding mechanism and the applications in aqueous solution. Systematic study on the characteristics and properties of the complex in solid phase after the binding of curcumin with protein is scarce. In this work, a powder composite of curcumin bound to ovalbumin was prepared by freeze-drying. The FTIR and X-ray diffraction results indicated that the crystal structure of curcumin and secondary structure of ovalbumin were changed because of the binding of curcumin to ovalbumin, leading to the formation of an amorphous complex with the sizes in the range of 924.20 ± 72.34 nm. Thermogravimetric analysis showed that the maximum weight loss point of ovalbumin/curcumin complex was at 289 °C, which was lower than that of pure ovalbumin and curcumin, implying that the complex was more prone to pyrolyze. Furthermore, the improved antioxidant activity was evaluated by DPPH radical scavenging activity and reducing power assay compared with pure ovalbumin and curcumin. This work could help to understand the characteristics of the curcumin-protein complex which has the potential to be applied in functional foods.

Tuning the Hydrophilic/Hydrophobic Balance to Control the Structure of Chitosan Films and Their Protein Release Behavior.

The control over the crystallinity of chitosan and chitosan/ovalbumin films can be achieved via an appropriate balance of the hydrophilic/hydrophobic interactions during the film formation process, which then controls the release kinetics of ovalbumin. Chitosan films were prepared by solvent casting. The presence of the anhydrous allomorph can be viewed as a probe of the hydrophobic conditions at the neutralization step. The semicrystalline structure, the swelling behavior of the films, the protein/chitosan interactions, and the release behavior of the films were impacted by the DA and the film processing parameters. At low DAs, the chitosan films neutralized in the solid state corresponded to the most hydrophobic environment, inducing the crystallization of the anhydrous allomorph with and without protein. The most hydrophilic conditions, leading to the hydrated allomorph, corresponded to non-neutralized films for the highest DAs. For the non-neutralized chitosan acetate (amorphous) films, the swelling increased when the DA decreased, whereas for the neutralized chitosan films, the swelling decreased. The in vitro release of ovalbumin (model protein) from chitosan films was controlled by their swelling behavior. For fast swelling films (DA = 45%), a burst effect was observed. On the contrary, a lag time was evidenced for DA = 2.5% with a limited release of the protein. Furthermore, by blending chitosans (DA = 2.5% and 45%), the release behavior was improved by reducing the burst effect and the lag time. The secondary structure of ovalbumin was partially maintained in the solid state, and the ovalbumin was released under its native form.

High intensity ultrasound modified ovalbumin: Structure, interface and gelation properties

Influence of high intensity ultrasound (HIUS) on the structure and properties of ovalbumin (OVA) were investigated. It was found that the subunits and secondary structure of OVA did not change significantly with HIUS treatment from the electrophoretic patterns and circular dichroism (CD) spectrum. The amount of free sulfhydryl groups increased and intrinsic fluorescence spectra analysis indicated changes in the tertiary structure and partial unfold of OVA after sonication increased. Compared with the untreated OVA, HIUS treatment increased the emulsifying activity and foaming ability, and decreased interface tension (oil–water and air–water interface), which due to the increased surface hydrophobicity and decreased the surface net charge in OVA, while the emulsifying and foaming stability had no remarkable differences. The increased particle size may be attributed to formation of protein aggregates. Moreover, the gelation temperatures of HIUS-treated samples were higher than the untreated OVA according to the temperature sweep model rheology, and this effect was consistent with the increased in surface hydrophobicity for ultrasound treated OVA. These changes in functional properties of OVA would promote its application in food industry.

Structural changes induced by heating affect ovalbumin-antigen processing and reduce allergic response in mouse model of food allergy

Background Food allergy is a serious health concern affecting about 8% of young children and about 3% of adults. The egg protein ovalbumin belongs among six frequent food allergens. Our goal was to develop the mouse model of ovalbumin food allergy and investigate how thermal processing affects its ability to induce allergic responses. Methods Effect of thermal processing (70°C and 95°C) on an ovalbumin secondary structure was characterized by circular dichroism and by kinetics of pepsin digestion with subsequent HPLC analysis. BALB/c mice were sensitized intraperitoneally and challenged intragastrically with native form or thermal processed ovalbumin (70°C). Clinical symptoms (allergic diarrhea, weight and temperature) were observed during the mice challenging. Levels of allergen-specific serum antibodies were determined by ELISA (IgA, IgG1 and IgG2a) by beta-hexosaminidase release test (IgE). Cytokine production (IL-4, IL-5, IL-6, IL-10, IL-13, IL-17, IFN-gamma) and mast cell protease-1 activity were assessed by ELISA. The activities of brush-border hydrolases were determined in the jejunum of treated mice. Results Heating of ovalbumin caused slight irreversible changes in secondary structure and significantly decreased clinical symptoms (allergic diarrhea). The thermal processing also decreased immune allergic response on the level of IgE, IL-4, IL-5, IL-13. Furthermore, thermal-processed ovalbumin induced lower activities of serum mast cell protease-1 and enterocyte brush border membrane alkaline phosphatase as compared to native ovalbumin. On the other hand, thermal-processed ovalbumin stimulated higher IgG2a antibodies in sera and IFN-gamma secretion by splenocytes. Conclusion In our mice model of food allergy, we show that even a slight change in the secondary structure of ovalbumin after thermal processing reduces its allergenicity and induces shift towards Th1 immune responses. At present, we utilize this model for studying of food allergy in germfree mice.

Preparation and characterization of ovalbumin and carboxymethyl cellulose conjugates via glycosylation

Protein and polysaccharide complex has aroused increasing interest in food applications. In this study, ovalbumin (OVA) and carboxymethyl cellulose (CMC) conjugates were prepared by glycosylation reaction and characterized by SDS-PAGE, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and circular dichroism (CD) analysis. The degree of grafting (DG) and browning index (OD) increased with reaction time and 8 d was selected as the optimized reaction time to equilibrium the glycosylation and unfavorable browning effect. The weight ratio (OVA: CMC) was optimized at 4:1 and pH was 7 or 8. The glycosylation grafting was proven by SDS-PAGE and FTIR. DSC showed that the thermal stability of OVA was improved after glycosylation reaction, which was positively related with molecular weight and the degree of substitution DS of CMC. From CD spectra, the secondary structure of OVA was affected by the grafted CMC with increasing β-sheet and random coil and decreasing α-helix and β-turns. The information obtained from this study can enrich the theoretical frame of protein and polysaccharide interaction, broaden the possible applications of food ingredients from egg source and polysaccharide, and provide the theory evidence on developing tailored egg powder.

Mechanism for formation of ovalbumin–fatty acid salt mixed gels

In this study, changes in the secondary structure of ovalbumin (OVA) during sodium caprate-induced gel formation were analyzed by FT-IR to help clarify mechanisms of protein gelation. Due to aggregation, there was an increase in intermolecular β-sheet bands and a decrease in α-helix and intramolecular β-sheet content during sodium caprate-induced gel formation. Furthermore, heat treatment of the gel caused a further enhancement in the content of intermolecular β-sheet bands. These results suggest that, similar to β-lactoglobulin gels, sodium caprate-induced OVA gels and heat-induced OVA gels form by similar mechanisms, although the sodium caprate-induced gel formation is accompanied by less marked changes in protein conformation.

Emulsifying and structural properties of ovalbumin

The emulsifying properties of ovalbumin were investigated, and the relationships between the emulsifying properties and protein structure were also discussed. The emulsifying properties of ovalbumin were dependent on pH, concentration of protein dispersion, oil-phase volume, and presence of salts. The pH was the most important variable in the emulsifying activity. The emulsifying activity of ovalbumin was relatively high in the acidic pH region. The surface hydrophobicity of ovalbumin was greater at acidic pHs than at neutral pHs. No significant difference was found between the secondary structure of ovalbumin at pH 3 and that at pH 7, but microenvironmental changes were shown around the aromatic amino acid residues in acid solution. The line widths of 31P NMR spectra in ovalbumin at pH 3 or 8 suggested that the conformation of ovalbumin was more flexible at acidic pHs than at neutral pHs. Thus, the high emulsifying activity of ovalbumin at acidic phs was assumed to correlate with the greater surface hydrophobicity and flexibility of the molecule.

Helix stability in succinylated and acetylated ovalbumins: effect of high pH, urea and guanidine hydrochloride

Previous studies (Batra, P.P., Roebuck, M.A. and Uetrecht, D. (1990) J. Protein Chem. 9, 37–44) showed that succinylation or acetylation of 75% of the lysine residues has little effect on the secondary structure of ovalbumin. The acylation of the remaining 25% lysine residues, which apparently are partially buried, results in a substantial loss of the helical structure. These conformational changes may be due not only to electrostatic repulsions introduced by succinylation or acetylation of the positively charged ε-amino groups but also to steric hindrance, since an increase in the ionic strength failed to reverse the loss of the helical structure. An increase in pH to 12.2 results in a complete helix-to-coil transition in the maximally succinylated ovalbumin (but not in the partially succinylated or in any of the acetylated ovalbumins including the maximally acetylated derivative), perhaps because it is most expanded and its molecular interior most accessible to solvent as succinylation replaces +1 charge of ε-amino group with a −1 charge so that a net of −2 charge per succinyl group is placed on the protein molecule. This helix-to-coil transition in the maximally succinylated ovalbumin induced by high pH is fully reversed by increasing the ionic strength, indicating that only electrostatic effects are responsible for this disruption. Studies have also shown that although there is no loss of the helical structure until after the 75% surface lysine residues have been acylated, the helical structure does become progressively destabilized with increasing degree of modification, a conclusion drawn from urea unfolding curves. This destabilization of the helical structure is due primarily to electrostatic effects, as an increase in the ionic strength led to an increase in the urea transition mid-point. Unlike urea, the guanidine hydrochloride unfolding curves indicate that the transition mid-point for the native protein, as well as for the maximally succinylated and acetylated derivatives, is about the same, perhaps because the denaturant itself acts as an electrolyte.

Effect of lysine modification on the secondary structure of ovalbumin

In order to determine the effect of chemical modification of the epsilon-amino groups on the secondary structure of ovalbumin, we prepared six acetylated (17, 36, 54, 70, 82, and 98%) and four succinylated derivatives (25, 50, 72, and 97%) of the protein. Native ovalbumin and the acylated derivatives were homogeneous as revealed by the electrophoretic pattern. The UV-absorption and fluorescence spectra changed progressively with the extent of modification. However, circular dichroic (CD) studies indicated that acylation of 15 of the 20 lysine residues had little effect on the secondary structure of ovalbumin. Acylation of the remaining five lysine residues resulted in a fairly severe change in the secondary structure. The alpha-helical content decreased from about 31% in the native state to 16.5% in the 97% succinylated ovalbumin and to 21.5% in the 98% acetylated derivative. A comparison of these data with the spectral and hydrodynamic data of Qasim and Salahuddin (1978) suggested that the secondary structure of ovalbumin is more resistant to acylation than is the tertiary structure and, thus, the tertiary and the secondary structures are, to some extent, mutually independent. Raising the pH to 11.2 did not alter the secondary structure of ovalbumin and increasing the ionic strength by more than 20-fold did not reverse the loss of helical structure in 97% succinylated protein. These two observations suggest that the change in secondary structure upon maximal acylation may not only involve electrostatic effects, but also certain other factors, such as steric hindrance due to the entering bulky groups.