Binding of β-lactoglobulin to three phenolics improves the stability of phenolics studied by multispectral analysis and molecular modeling.
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ABSTRACT:
SUBMITTER: Zhang S
PROVIDER: S-EPMC9234335 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Bovine beta-lactoglobulin A assumes a dimeric native conformation at neutral pH, while the conformation at pH 2 is monomeric but still native. Beta-lactoglobulin A has a free thiol at Cys121, which is buried between the beta-barrel and the C-terminal major alpha-helix. This thiol group was specifically reacted with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) in the presence of 1.0 M Gdn-HCI at pH 7.5, producing a modified beta-lactoglobulin (TNB-bIg) containing a mixed disulfide bond with 5-thio-2-nitrobenzoic acid (TNB). The conformation and stability of TNB-bIg were studied by circular dichroism (CD), tryptophan fluorescence, analytical ultracentrifugation, and one-dimensional 1H-NMR. The CD spectra of TNB-bIg indicated disordering of the native secondary structure at pH 7.5, whereas a slight increase in the alpha-helical content was observed at pH 2.0. The tryptophan fluorescence of TNB-bIg was significantly quenched compared with that of the intact protein, probably by the energy transfer to TNB. Sedimentation equilibrium analysis indicated that, at neutral pH, TNB-bIg is monomeric while the intact protein is dimeric. In contrast, at pH 2.0, both the intact beta-lactoglobulin and TNB-bIg were monomeric. The unfolding transition of TNB-bIg induced by Gdn-HCl was cooperative in both pH regions, although the degree of cooperativity was less than that of the intact protein. The 1H-NMR spectrum for TNB-bIg at pH 3.0 was native-like, whereas the spectrum at pH 7.5 was similar to that of the unfolded proteins. These results suggest that modification of the buried thiol group destabilizes the rigid hydrophobic core and the dimer interface, producing a monomeric state that is native-like at pH 2.0 but is molten globule-like at pH 7.5. Upon reducing the mixed disulfide of TNB-bIg with dithiothreitol, the intact beta-lactoglobulin was regenerated. TNB-bIg will become a useful model to analyze the conformation and stability of the intermediate of protein folding.
| S-EPMC2144692 | biostudies-other
Project description:We study microtubular supramolecular architectures of tubulin dimers self-assembling into linear protofilaments, in turn forming a closed tube, which is an important component of the cytoskeleton. We identify the protofilament arrangements with the lowest free energy using molecular dynamics to optimize tubulin conformations. We then use the three-dimensional molecular theory of solvation to obtain the hydration structure of protofilaments built of optimized tubulins and the solvent-mediated effective potential between them. The latter theoretical method, based on first principles of statistical mechanics, is capable of predicting the structure and thermodynamics of solvation of supramolecular architectures. We obtained a set of profiles of the potential of mean force between protofilaments in a periodic two-dimensional sheet in aqueous solution. The profiles were calculated for a number of amino acid sequences, tubulin conformations, and spatial arrangements of protofilaments. The results indicate that the effective interaction between protofilaments in aqueous solution depends little on the isotypes studied; however, it strongly depends on the M loop conformation of beta-tubulin. Based on the analysis of the potential of mean force between adjacent protofilaments, we found the optimal arrangement of protofilaments, which is in good agreement with other studies. We also decomposed the potential of mean force into its energetic and entropic components, and found that both are considerable in the free-energy balance for the stabilized protofilament arrangements.
| S-EPMC1751377 | biostudies-literature
Project description:There is a need to understand the ultrasound-induced changes in the interactions between proteins and phenolic compounds at different pH. This study systematically explored the role of high-intensity ultrasound pre-treatment on the binding mechanisms of β-lactoglobulin (β-LG) to two common phenolic compounds, i.e., (-)-epigallocatechin-3-gallate (EGCG) and chlorogenic acid (CA) at neutral and acidic pH (pH 7.2 and 2.4). Tryptophan fluorescence revealed that compared to proteins sonicated at 20% and 50% amplitudes, 35%-amplitude ultrasound pre-treatment (ULG-35) strengthened the binding affinities of EGCG/CA to β-LG without altering the main interaction force. After phenolic addition, ULG-35 displayed a similar but a greater extent of protein secondary and tertiary structural changes than the native protein, ascribed to the ultrasound-driven hydrophobic stacking among interacted molecules. The dominant form of β-LG (dimer/monomer) played a crucial role in the conformational and interfacial properties of complexes, which can be explained by the distinct binding sites at different pH as unveiled by molecular docking. Combining pre-ultrasound with EGCG interaction notably increased the foaming and emulsifying properties of β-LG, providing a feasible way for the modification of bovine whey proteins. These results shed light on the understanding of protein-phenolic non-covalent binding under ultrasound and help to develop complex systems with desired functionality and delivery.
| S-EPMC8190473 | biostudies-literature
Project description:PurposeGastric injury is a major issue for long-term administration of aspirin. In this work, we tried to explore the possibility of using BLG to alleviate aspirin-induced gastric injury, because of excellent abilities of BLG in loading drug molecules.MethodsVarious spectroscopic techniques and molecular docking methods were applied to investigate the interaction mechanism between BLG and aspirin. Animal experiments were performed to figure out the effects of taking aspirin-BLG on the stomach.ResultsOur results demonstrate that aspirin could bind with BLG to form stable aspirin-BLG complex (the binding constant Kb = 2.051 × 103 M-1). The formation process is endothermic (∆H>0) and the main acting force is hydrophobic force. Our data also show that the aspirin-BLG complex is formed with a higher affinity in simulated gastric fluid and could remain stable for several hours, which might arise from its special binding mode under acidic condition and the resistance of BLG to gastric digestion. Furthermore, animal models (rats with aspirin-induced gastric damage) were built. The results of animal experiments reveal that the oral administration of aspirin-BLG could cause less damage to gastric tissue, and it also hardly triggers obvious inflammatory responses.ConclusionThis study would contribute to an in-depth understanding of the interaction mechanism between BLG and aspirin. It is reasonable to believe that using BLG to bind with aspirin would be a potential way to alleviate the aspirin-induced gastric injury.
| S-EPMC8898184 | biostudies-literature
Project description:Ligand-binding properties of β-lactoglobulin (β-lg) are well documented, but the subsequent biological functions are still unclear. Focusing on fatty acids/β-lg complexes, the structure-function relationships are reviewed in the light of the structural state of the protein (native versus non-native aggregated proteins). After a brief description of β-lg native structure, the review takes an interest in the binding properties of native β-lg (localization of binding sites, stoichiometry, and affinity) and the way the interaction affects the biological properties of the protein and the ligand. The binding properties of non-native aggregated forms of β-lg that are classically generated during industrial processing are also related. Structural changes modify the stoichiometry and the affinity of β-lg for fatty acids and consequently the biological functions of the complex. Finally, the fatty acid-binding properties of other whey proteins (α-lactalbumin, bovine serum albumin) and some biological properties of the complexes are also addressed. These proteins affect β-lg/fatty acids complex in whey given their competition with β-lg for fatty acids.
| S-EPMC4121524 | biostudies-literature
Project description:High pressure (HP) is a particularly powerful tool to study protein folding/unfolding, revealing subtle structural rearrangements. Bovine β-lactoglobulin (BLG), a protein of interest in food science, exhibits a strong propensity to bind various bioactive molecules. We probed the effects of the binding of biliverdin (BV), a tetrapyrrole linear chromophore, on the stability of BLG under pressure, by combining in situ HP small-angle neutron scattering (SANS) and HP-UV absorption spectroscopy. Although BV induces a slight destabilization of BLG during HP-induced unfolding, a ligand excess strongly prevents BLG oligomerization. Moreover, at SANS resolution, an excess of BV induces the complete recovery of the protein "native" 3D structure after HP removal, despite the presence of the BV covalently bound adduct. Mass spectrometry highlights the crucial role of cysteine residues in the competitive and protective effects of BV during pressure denaturation of BLG through SH/S-S exchange.
| S-EPMC9300659 | biostudies-literature
Project description:The thermodynamic stability of beta-lactoglobulin (beta-Lg) was studied at acidic and near-neutral pH values using equilibrium thermal-unfolding measurements. Transition temperature increased with a decrease in pH from 7.5 to 6.5 and 3.0 to 1.5, suggesting an increase in the net protein stability. Determination of the change in free energy of unfolding and extrapolation into the nontransition region revealed that beta-Lg increases its stability by increasing the magnitude of the change in free energy of unfolding at the temperature of maximum stability, as well as by increasing the temperature of maximum stability. The relative difference in the change in free energy of unfolding at 70 degrees C (with a reference pH of 7.5) was positive and its magnitude increased with a decrease in pH from 7.0 to 1.5 van't Hoff plots of thermal unfolding of beta-Lg at all pH values studied were non-linear and the measured changes in the enthalpy and entropy of unfolding for beta-Lg were high and positive. The relative magnitude of change of both enthalpy and entropy at 70 degrees C (compared with pH 7.5) increased with a decrease in pH up to 1.5. A possible mechanism for the increased stability of beta-Lg at low pH is discussed.
| S-EPMC1135197 | biostudies-other
Project description:Based on the fact that β-lactoglobulin (β-lg) can solubilize readily in water and bind many small hydrophobic molecules, a novel nanocomplexed glabridin with β-lg was developed by an antisolvent precipitation method. After binding to β-lg, the solubility of glabridin in aqueous solution was enhanced 21 times. Fluorescence spectroscopy of β-lg revealed that the interaction of glabridin with β-lg made the environment of Trp and Tyr residues on β-lg more hydrophilic. The morphology and crystal form of the nanocomplexed glabridin with β-lg was characterized and the changes in β-lg conformation was also been investigated. In combination with molecular docking modeling, the results revealed that glabridin was bound to β-lg by hydrophobic forces and hydrogen-bond interactions. Furthermore, the nanocomplexed glabridin with β-lg had a better 2,2-diphenyl-1-picrylhydrazyl radical-scavenging capacity and 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulfonic acid radical-scavenging capacity compared to free glabridin at the same concentration during in vitro tests. Thus, nanocomplexing with β-lg, by virtue of its ability to enhance the solubility of glabridin in aqueous systems, provides a suitable opportunity as a nanocarrier molecule.
| S-EPMC6645583 | biostudies-literature
Project description:Piceatannol (PIC) and epigallocatechin gallate (EGCG) are polyphenolic compounds with applications in the treatment of various diseases such as cancer, but their stability is poor. β-lactoglobulin (β-LG) is a natural carrier that provides a protective effect to small molecule compounds and thus improves their stability. To elucidate the mechanism of action of EGCG, PIC, and palmitate (PLM) in binding to β-LG individually and jointly, this study applied molecular docking and molecular dynamics simulations combined with in-depth analyses including noncovalent interaction (NCI) and binding free energy to investigate the binding characteristics between β-LG and compounds of PIC, EGCG, and PLM. Simulations on the binary complexes of β-LG + PIC, β-LG + EGCG, and β-LG + PLM and ternary complexes of (β-LG + PLM) + PIC, (β-LG + PLM) + EGCG, β-LG + PIC) + EGCG, and (β-LG + EGCG) + PIC were performed for comparison and characterizing the interactions between binding compounds. The results demonstrated that the co-bound PIC and EGCG showed non-beneficial effects on each other. However, the centrally located PLM was revealed to be able to adjust the binding conformation of PIC, which led to the increase in binding affinity with β-LG, thus showing a synergistic effect on the co-bound PIC. The current study of β-LG co-encapsulated PLM and PIC provides a theoretical basis and research suggestions for improving the stability of polyphenols.
| S-EPMC10933772 | biostudies-literature
Project description:?-lactoglobulin (LG) contains nine ?-strands (strands A-I) and one ?-helix. Strands A-H form a ?-barrel. At neutral pH, equine LG (ELG) is monomeric, whereas bovine LG (BLG) is dimeric, and the I-strands of its two subunits form an intermolecular ?-sheet. We previously constructed a chimeric ELG in which the sequence of the I-strand was replaced with that of BLG. This chimera did not dimerize. For this study, we constructed the new chimera we call Gyuba (which means cow and horse in Japanese). The amino acid sequence of Gyuba includes the sequences of the BLG secondary structures and those of the ELG loops. The crystal structure of Gyuba is very similar to that of BLG and indicates that Gyuba dimerizes via the intermolecular ?-sheet formed by the two I-strands. Thus, the entire arrangement of the secondary structural elements is important for LG dimer formation.
| S-EPMC3267951 | biostudies-literature