Interactions between bovine beta-lactoglobulin A and various bioactive peptides as studied by front-face fluorescence spectroscopy

The Effect of Sulfobetaine Coating in Inhibiting the Interaction between Lyotropic Liquid Crystalline Nanogels and Proteins

The injective lyotropic liquid crystalline nanogels (LLCNs) were widely used in drug delivery systems. But when administered in vivo, LLCNs exposed to the biological environment interact with proteins. Recently, it has been shown that nanoparticles coated with zwitterions can inhibit their interaction with proteins. Thus, in this study, the interaction between proteins and LLCNs coated with the zwitterionic material sulfobetaine (GLLCNs@HDSB) was investigated using bovine serum albumin (BSA) as a model protein. Interestingly, it was found that GLLCNs@HDSB at higher concentrations (≥0.8 mg/mL) could block its interaction with BSA, but not at lower concentrations (<0.8 mg/mL), according to the results of ultraviolet, fluorescence, and circular dichroism spectra. In the ultraviolet spectra, the absorbance of GLLCNs@HDSB (0.8 mg/mL) was 1.9 times higher than that without the sulfobetaine coating (GLLCNs) after incubation with protein; the fluorescence quenching intensity of GLLCNs@HDSB was conversely larger than that of the GLLCNs; in circular dichroism spectra, the ellipticity value of GLLCNs@HDSB was significantly smaller than that of the GLLCNs, and the change in GLLCNs@HDSB was 10 times higher than that of the GLLCNs. Generally, nanoparticles coated with sulfobetaine can inhibit their interaction with proteins, but in this study, LLCNs showed a concentration-dependent inhibitory effect. It could be inferred that in contrast to the surface of nanoparticles covered with sulfobetaine in other cases, the sulfobetaine in this study interacted with the LLCNs and was partially inserted into the hydrophobic region of the LLCNs. In conclusion, this study suggests that coating-modified nanoparticles do not necessarily avoid interacting with proteins, and we should also study coating-modified nanoparticles interacting with proteins both in vitro and in vivo. In the future, finding a coating material to completely inhibit the interaction between LLCNs and proteins will generate a great impetus to promote the clinical transformation of LLCNs.

Two different protein corona formation modes on Soluplus® nanomicelles

Soluplus® nanomicelles have been widely reported in biomedical field for their excellent drug loading capacity and solubility enhancement ability. However, when administrated in vivo, the protein corona will be formed on Soluplus® nanomicelles, significantly affecting their drug delivery performance. Up to now, few studies examined the protein corona formation process and its impact factors of Soluplus® nanomicelles. The multiple proteins in biofluids may form protein corona in different modes due to their diversified properties. In this study, Bovine serum albumin (BSA), Lysozyme (Lyso) and Bovine hemoglobin (BHb) were chosen as model proteins to investigate the protein corona formation process of Soluplus® nanomicelles. By analyzing the polarity of the protein amino acid residues distributing microenvironments, the results showed that there were two different protein corona formation modes, i.e., surface adsorption and insertion, which were determined by the hydrophilicity of proteins. The hydrophobic BHb followed the insertion mode while hydrophilic BSA and Lyso followed the surface adsorption mode. Ultimately, upon protein corona formation, the size and surface chemistry of nanomicelles was significantly affected. We believe this study will provide a new research paradigm to the design and application of Soluplus® nanomicelles.

Identification and Detection of Bioactive Peptides in Milk and Dairy Products: Remarks about Agro-Foods

Food-based components represent major sources of functional bioactive compounds. Milk is a rich source of multiple bioactive peptides that not only help to fulfill consumers 'nutritional requirements but also play a significant role in preventing several health disorders. Understanding the chemical composition of milk and its products is critical for producing consistent and high-quality dairy products and functional dairy ingredients. Over the last two decades, peptides have gained significant attention by scientific evidence for its beneficial health impacts besides their established nutrient value. Increasing awareness of essential milk proteins has facilitated the development of novel milk protein products that are progressively required for nutritional benefits. The need to better understand the beneficial effects of milk-protein derived peptides has, therefore, led to the development of analytical approaches for the isolation, separation and identification of bioactive peptides in complex dairy products. Continuous emphasis is on the biological function and nutritional characteristics of milk constituents using several powerful techniques, namely omics, model cell lines, gut microbiome analysis and imaging techniques. This review briefly describes the state-of-the-art approach of peptidomics and lipidomics profiling approaches for the identification and detection of milk-derived bioactive peptides while taking into account recent progress in their analysis and emphasizing the difficulty of analysis of these functional and endogenous peptides.

Discordance between in silico & in vitro analyses of ACE inhibitory & antioxidative peptides from mixed milk tryptic whey protein hydrolysate

ACE inhibitory and antioxidative peptides identified by LCMS/MS, from mixed milk (Bubalus bubalis and Bos taurus) tryptic whey protein hydrolysate, were compared with the in silico predictions. α la and ß lg sequences, both from Bubalus bubalis and Bos taurus, were used for in silico study. SWISS-PROT and BIOPEP protein libraries were accessed for prediction of peptide generation. Study observed gaps in the prediction versus actual results, which remain unaddressed in the literature. Many peptides obtained in vitro, were not reflected in in silico predictions. Differences in identified peptides in separate libraries were observed too. In in silico prediction, peptides with known biological activities were also not reflected. Predictions, towards generation of bioactive peptides, based upon in silico release of proteins and amino acid sequences from different sources and thereupon validation in relation to actual results has often been reported in research literature. Given that computer aided simulation for prediction purposes is an effective research direction, regular updating of protein libraries and an effectual integration, for more precise results, is critical. The gaps addressed between these two techniques of research, have not found any address in literature. Inclusion of more flexibility with the variables, within the tools being used for prediction, and a hierarchy based database with search options for various peptides, will further enhance the scope and strength of research.

Inverse Temperature Dependence in Static Quenching versus Calorimetric Exploration: Binding Interaction of Chloramphenicol to β-Lactoglobulin

The binding interaction between the whey protein bovine β-lactoglobulin (βLG) with the well-known antibiotic chloramphenicol (Clp) is explored by monitoring the intrinsic fluorescence of βLG. Steady-state and time-resolved fluorescence spectral data reveal that quenching of βLG fluorescence proceeds through ground state complex formation, i.e., static quenching mechanism. However, the drug-protein binding constant is found to vary proportionately with temperature. This anomalous result is explained on the basis of the Arrhenius theory which states that the rate constant varies proportionally with temperature. Thermodynamic parameters like ΔH, ΔS, ΔG, and the stoichiometry for the binding interaction have been estimated by isothermal titration calorimetric (ITC) study. Thermodynamic data show that the binding phenomenon is mainly an entropy driven process suggesting the major role of hydrophobic interaction forces in the Clp-βLG binding. Constant pressure heat capacity change (ΔCp) has been calculated from enthalpy of binding at different temperatures which reveals that hydrophobic interaction is the major operating force. The inverse temperature dependence in static quenching is however resolved from ITC data which show that the binding constant regularly decreases with increase in temperature. The modification of native protein conformation due to binding of drug has been monitored by circular dichroism (CD) spectroscopy. The probable binding location of Clp inside βLG is explored from AutoDock based blind docking simulation.

Interactions of β-lactoglobulin variants A and B with Vitamin A. Competitive binding of retinoids and carotenoids

β-Lactoglobulin (β-Lg) is the major whey protein of bovine milk present at a concentration of 2-3 g L(-1). Its biological role is still not well-known. However, many studies have suggested that β-Lg may play either nutritional or specific transporter role. The high affinity of β-Lg for retinol and other retinoids was reported. The results of interaction studies of β-Lg with carotenoids, that is, β-carotene, β-cryptoxanthin, and α-carotene, which display similar structures are reported in this study. The affinities of β-Lg for binding of retinoids and carotenoids were compared, providing more information about the binding site(s) of these molecules by β-Lg. Interactions were followed by the measurements of quenching of β-Lg tryptophan fluorescence and retinol fluorescence. The obtained results indicate that carotenoids are bound by β-Lg with high affinity of the order of 10(-8) M. Measurement of retinol competition with carotenoids for binding by β-Lg suggests that the binding of these two ligands occurs at two different sites of β-Lg.

Antihypertensive peptides: production, bioavailability and incorporation into foods

Bioactive food peptides are encrypted within the sequence of food proteins but can be released during food processing (by enzymatic hydrolysis or fermentation) or during gastrointestinal transit. Among bioactive food peptides, those with antihypertensive activity are receiving special attention due to the high prevalence of hypertension in the Western countries and its role in cardiovascular diseases. This paper reviews the current literature on antihypertensive food peptides, focusing on the main methodologies for their production, such as enzymatic hydrolysis, fermentation and the use of recombinant bacteria. This paper also describes the structure/activity relationship of angiotensin-converting enzyme (ACE)-inhibitory peptides, as well as their bioavailability, physiological effects demonstrated by both in vitro and in vivo assays, and the contribution of mechanisms of action other than ACE inhibition. Finally, current reported strategies for incorporation of antihypertensive peptides into foods and their effects on both availability and activity are revised in this manuscript.

Binding of phenolic compounds and their derivatives to bovine and reindeer beta-lactoglobulin

In plant-based food, phenolic compounds usually do not exist in their native form, but as esters, glycosides, or polymers. The native forms, however, require deglycosylation for their intestinal absorption, and aglycone has been considered to be the potential health-protecting/promoting form. The binding of the aglycones of phenolic compounds to bovine and reindeer beta-lactoglobulins (betaLG) using fluorescence quenching was studied. The effects of pH and storage were also studied. Of the compounds investigated, the majority of flavones, flavonols, flavanones, and isoflavones were bound to betaLG. In the pH studies, no significant effects were found. The fact that the phenolic compounds were not released at pH 2 might indicate that they bind to an external part rather than to the central cavity. Studies implicated that betaLG could act as a binder or carrier for phenolic compounds in acidic, basic, or neutral conditions and that the ligand/betaLG complex can remain stable during storage.