Paper chromatography approach for the assessment of interaction between red wine and whole saliva

In-mouth interaction of red wine compounds with salivary proteins is a primary event allegedly responsible for eliciting the mouth-feel sensation of astringency. Those interactions have been currently associated with precipitation of salivary protein/polyphenol complexes. However, such single physicochemical evidence for interaction does not account for the complexity of astringency. This study aimed to develop a paper chromatography method to assess interactions between red wine and the salivary protein fraction using stepwise series of red wine/saliva binary mixtures from 100% wine to 100% saliva ("Alpha and Omega series"). Aliquots of each one of the mixtures were spotted on a cellulose membrane to scrutinize independently the distribution areas of wine components (naturally pink-colored) and salivary protein (stained blue in Coomassie Brilliant R-250). This double target detection revealed interactions between saliva and red wine components along most of the quantitative Alpha and Omega series, a point of equivalence corresponding to maximum interactivity for both complex reactants and a non-diffusible sub-fraction of saliva displaying the highest interactivity. The results indicate a novel way to assess quantitatively physicochemical interactions between red wines and human saliva but also provide new lights to approach the identification of molecular salivary structures involved in triggering astringency.

Horner-Wadsworth-Emmons reaction as an excellent tool in the synthesis of fluoro-containing biologically important compounds

Selective introduction of a double bond motif into a multifunctional organic compound is always a big challenge. The Horner-Wadsworth-Emmons reaction is one of the most reliable, simple, and stereoselective olefination methods, widely used in organic chemistry. To the best of our knowledge, no review article on the application of HWE reaction in the synthesis of fluoroorganic compounds with direct biological interest has been published in recent years. The importance of the HWE reaction should be emphasised due to its simplicity and stereoselectivity. Under mild conditions and in one step, valuable compounds can be obtained. The HWE reaction is primarily a great tool in the synthesis of fluoroolefins that are, among others, peptide bond mimetics. Therefore, it can serve as an indispensable approach to access peptide bioisosteres and, consequently, analogues of numerous enzyme inhibitors. The protocol may be utilized to obtain florinated vinylphosphonate, vinylsulfone or sulfonate derivatives, which exhibit biological activity. In this review article, we would like to summarize the HWE reaction output of the last 12 years (since 2010).

A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties

Caseins (α_S1, α_S2, β and κ) are the main protein fraction of bovine milk. Together with nanoclusters of amorphous calcium phosphate (CaP) and divalent cations, they combine to form a polydisperse distribution of particles called casein micelles. A casein micelle model is proposed which is consistent with the way in which intrinsically disordered proteins interact through predominantly polar, short, linear, motifs. Using the model, an expression is derived for the size distribution of casein micelles formed when caseins bind to the CaP nanoclusters and the complexes further associate with each other and the remaining mixture of free caseins. The result is a refined coat-core model in which the core is formed mainly by the nanocluster complexes and the coat is formed exclusively by the free caseins. Example calculations of the size distribution and surface composition of an average bovine milk are compared with experiment. The average size, size distribution and surface composition of the micelles is shown to depend on the affinity of the nanocluster complexes for each other in competition with their affinity for free caseins, and on the concentrations of free caseins, calcium ions and other salts in the continuous phase.

Characterization and analysis of antioxidant activity of walnut-derived pentapeptide PW5 via nuclear magnetic resonance spectroscopy

The antioxidative activity of natural products has commonly been studied by free radical scavenging methods. However, the mechanisms by which antioxidation is explored by free radical scavenging methods remain largely unknown. This study analyzed the composition of walnut-derived pentapeptides PW5 with potential biological activity and its oxidation reaction products in 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) test by nuclear magnetic resonance (NMR) spectroscopy. The amino acid sequence of PW5 peptide successfully characterized as Proline-Proline-Lysine-Asparagine-Tryptophan exhibited significant antioxidant activity with lower IC₅₀ value (0.2210 ± 0.0032 mM) compared to glutathione (GSH, 0.2567 ± 0.0023 mM, p < 0.001). Furthermore, we found that the tryptophan residue was the only residue in PW5 with obvious alteration after treatment with ABTS free radicals, which was linked to its potential antioxidant properties. These findings revealed how NMR-characterized structures and oxidation reaction products may be used to explore the antioxidative mechanisms of food-derived peptides as well as other natural products.

Natural Tannin Wood Extracts as a Potential Food Ingredient in the Food Industry

Wood extracts are one of the most important natural sources of industrially obtained tannins. Their use in the food industry could be one of the biggest (most important) recent innovations in food science as a result of their multiple (many) possible applications. The use of tannin wood extracts (TWEs) as additives directly added in foods or in their packaging meets an ever-increasing consumer demand for innovative approaches to sustainability. The latest research is focusing on new ways to include them directly in food, to take advantage of their specific actions to prevent individual pathological conditions. The present review begins with the biology of TWEs and then explores their chemistry, specific sensorial properties, and current application in food production. Moreover, this review is intended to cover recent studies dealing with the potential use of TWEs as a starting point for novel food ingredients.

Physicochemical interactions with (-)-epigallocatechin-3-gallate drive structural modification of celiac-associated peptide α2-gliadin (57-89) at physiological conditions

(-)-Epigallocatechin-3-gallate (EGCG), a major phenolic constituent of tea, has been shown to have biological activity within inflammatory pathways involved with food allergies and intolerances. Proposed mechanisms for this effect include sequestration and structural modification of immunostimulatory proteins as a result of interactions with EGCG. The present study employs biophysical techniques including dynamic light scattering, circular dichroism and nuclear magnetic resonance to elucidate the likely mechanism(s) by which EGCG interacts with α2-gliadin (57-89) (α2g), an immunodominant peptide in celiac disease pathogenesis. We demonstrate that EGCG interacts with α2g in a multi-phase reaction driven by non-specific binding, resulting in the formation of polydisperse EGCG/α2g complexes which induce changes in peptide structure. We also show that these interactions occur at a range of pH levels associated with digestion, including pH 2.0, 6.8 and 7.5. Based on previous reports of binding specificity of enzymes and antigen presenting cells in celiac disease pathogenesis, our results provide foundational support for EGCG to prevent recognition of immunostimulatory gliadin epitopes by the body and thus prevent the inflammatory and autoimmune response associated with celiac disease.

Interactions between wine phenolic compounds and human saliva in astringency perception

Astringency is a complex perceptual phenomenon involving several sensations that are perceived simultaneously. The mechanism leading to these sensations has been thoroughly and controversially discussed in the literature and it is still not well understood since there are many contributing factors. Although we are still far from elucidating the mechanisms whereby astringency develops, the interaction between phenolic compounds and proteins (from saliva, oral mucosa or cells) seems to be most important. This review summarizes the recent trends in the protein-phenol interaction, focusing on the effect of the structure of the phenolic compound on the interaction with salivary proteins and on methodologies based on these interactions to determine astringency.

Microsecond and nanosecond polyproline II helix formation in aqueous nanodrops measured by mass spectrometry

The 1.5 μs and <400 ns time constants for the formation of polyproline II helix structures in 21 and 16 residue peptides, respectively, are measured using rapid mixing from theta-glass emitters coupled with mass spectrometry. Results from these studies should serve as useful benchmarks for comparison with computational simulation results.

Label-free quantitative 1H NMR spectroscopy to study low-affinity ligand-protein interactions in solution: A contribution to the mechanism of polyphenol-mediated astringency

Nuclear magnetic resonance (NMR) spectroscopy is well-established in assessing the binding affinity between low molecular weight ligands and proteins. However, conventional NMR-based binding assays are often limited to small proteins of high purity and may require elaborate isotopic labeling of one of the potential binding partners. As protein–polyphenol complexation is assumed to be a key event in polyphenol-mediated oral astringency, here we introduce a label-free, ligand-focused ¹H NMR titration assay to estimate binding affinities and characterize soluble complex formation between proteins and low molecular weight polyphenols. The method makes use of the effects of NMR line broadening due to protein–ligand interactions and quantitation of the non-bound ligand at varying protein concentrations by quantitative ¹H NMR spectroscopy (qHNMR) using electronic reference to access in vivo concentration (ERETIC 2). This technique is applied to assess the interaction kinetics of selected astringent tasting polyphenols and purified mucin, a major lubricating glycoprotein of human saliva, as well as human whole saliva. The protein affinity values (BC₅₀) obtained are subsequently correlated with the intrinsic mouth-puckering, astringent oral sensation imparted by these compounds. The quantitative NMR method is further exploited to study the effect of carboxymethyl cellulose, a candidate “anti-astringent” protein binding antagonist, on the polyphenol–protein interaction. Consequently, the NMR approach presented here proves to be a versatile tool to study the interactions between proteins and low-affinity ligands in solution and may find promising applications in the discovery of bioactives.

To be disordered or not to be disordered: is that still a question for proteins in the cell?

There is ample evidence that many proteins or regions of proteins lack a well-defined folded structure under native-like conditions. These are called intrinsically disordered proteins (IDPs) or intrinsically disordered regions (IDRs). Whether this intrinsic disorder is also their main structural characteristic in living cells has been a matter of intense debate. The structural analysis of IDPs became an important challenge also because of their involvement in a plethora of human diseases, which made IDPs attractive targets for therapeutic development. Therefore, biophysical approaches are increasingly being employed to probe the structural and dynamical state of proteins, not only in isolation in a test tube, but also in a complex biological environment and even within intact cells. Here, we survey direct and indirect evidence that structural disorder is in fact the physiological state of many proteins in the proteome. The paradigmatic case of α-synuclein is used to illustrate the controversial nature of this topic.

Polyphenol Interactions Mitigate the Immunogenicity and Allergenicity of Gliadins

Wheat allergy is an IgE-mediated disorder. Polyphenols, which are known to interact with certain proteins, could be used to reduce allergic reactions. This study screened several polyphenol sources for their ability to interact with gliadins, mask epitopes, and affect basophil degranulation. Polyphenol extracts from artichoke leaves, cranberries, apples, and green tea leaves were examined. Of these extracts, the first three formed insoluble complexes with gliadins. Only the cranberry and apple extracts masked epitopes in dot blot assays using anti-gliadin IgG and IgE antibodies from patients with wheat allergies. The cranberry and artichoke extracts limited cellular degranulation by reducing mouse anti-gliadin IgE recognition. In conclusion, the cranberry extract is the most effective polyphenol source at reducing the immunogenicity and allergenicity of wheat gliadins.

Salivary proline-rich protein may reduce tannin-iron chelation: a systematic narrative review

Background

Tannins are often cited for antinutritional effects, including chelation of non-heme iron. Despite this, studies exploring non-heme iron bioavailability inhibition with long-term consumption have reported mixed results. Salivary proline-rich proteins (PRPs) may mediate tannin-antinutritional effects on non-heme iron bioavailability.

Aim

To review evidence regarding biochemical binding mechanisms and affinity states between PRPs and tannins, as well as effects of PRPs on non-heme iron bioavailability with tannin consumption in vivo.

Methods

Narrative systematic review and meta-analysis. Common themes in biochemical modeling and affinity studies were collated for summary and synthesis; data were extracted from in vivo experiments for meta-analysis.

Results

Thirty-two studies were included in analysis. Common themes that positively influenced tannin-PRP binding included specificity of tannin-PRP binding, PRP and tannin stereochemistry. Hydrolyzable tannins have different affinities than condensed tannins when binding to PRPs. In vivo, hepatic iron stores and non-heme iron absorption are not significantly affected by tannin consumption (d = −0.64-1.84; −2.7-0.13 respectively), and PRP expression may increase non-heme iron bioavailability with tannin consumption.

Conclusions

In vitro modeling suggests that tannins favor PRP binding over iron chelation throughout digestion. Hydrolyzable tannins are not representative of tannin impact on non-heme iron bioavailability in food tannins because of their unique structural properties and PRP affinities. With tannin consumption, PRP production is increased, and may be an initial line of defense against tannin-non-heme iron chelation in vivo. More research is needed to compare competitive binding of tannin-PRP to tannin-non-heme iron complexes, and elucidate PRPs’ role in adaption to non-heme iron bioavailability in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-017-0197-z) contains supplementary material, which is available to authorized users.

Epigallocatechin Gallate (EGCG) Inhibits Alpha-Synuclein Aggregation: A Potential Agent for Parkinson's Disease

Protein aggregation is a prominent feature of many neurodegenerative disorders including Parkinson's disease (PD). Aggregation of alpha-synuclein (SNCA) may underlie the pathology of PD. They are the main components of Lewy bodies and dystrophic neurites that are the intraneuronal inclusions characteristic of the disease. We have demonstrated that the polyphenol (-)-epi-gallocatechine gallate (EGCG) inhibited SNCA aggregation, which made it a candidate for therapeutic intervention in PD. Three methods were used: SNCA fibril formation inhibition by EGCG in incubates; inhibition of the SNCA fluorophore A-Syn-HiLyte488 binding to plated SNCA in microwells; and inhibition of the A-Syn-HiLyte488 probe binding to aggregated SNCA in postmortem PD tissue. Recombinant human SNCA was incubated under conditions that result in fibril formation. The aggregation was blocked by 100 nM EGCG in a concentration-dependent manner, as shown by an absence of thioflavin T binding. In the microplate assay system, the ED₅₀ of EGCG inhibition of A-Syn-HiLyte488 binding to coated SNCA was 250 nM. In the PD tissue based assay, SNCA aggregates were recognized by incubation with 7 nM of A-Syn-HiLyte488. This binding was blocked by EGCG in a concentration dependent manner. The SNCA amino acid sites, which potentially interacted with EGCG, were detected on peptide membranes. It was implicated that EGCG binds to SNCA by instable hydrophobic interactions. In this study, we suggested that EGCG could be a potent remodeling agent of SNCA aggregates and a potential disease modifying drug for the treatment of PD and other α-synucleinopathies.

Ethanol Concentration Influences the Mechanisms of Wine Tannin Interactions with Poly(L-proline) in Model Wine

Changes in ethanol concentration influence red wine astringency, and yet the effect of ethanol on wine tannin-salivary protein interactions is not well understood. Isothermal titration calorimetry (ITC) was used to measure the binding strength between the model salivary protein, poly(L-proline) (PLP) and a range of wine tannins (tannin fractions from a 3- and a 7-year old Cabernet Sauvignon wine) across different ethanol concentrations (5, 10, 15, and 40% v/v). Tannin-PLP interactions were stronger at 5% ethanol than at 40% ethanol. The mechanism of interaction changed for most tannin samples across the wine-like ethanol range (10-15%) from a combination of hydrophobic and hydrogen binding at 10% ethanol to only hydrogen binding at 15% ethanol. These results indicate that ethanol concentration can influence the mechanisms of wine tannin-protein interactions and that the previously reported decrease in wine astringency with increasing alcohol may, in part, relate to a decrease tannin-protein interaction strength.

Nature and consequences of non-covalent interactions between flavonoids and macronutrients in foods

Many of the potential health benefits of flavonoids have been associated with their specific chemical and biological properties including their ability to interact and bind non-covalently to macronutrients in foods. While flavonoid-protein interactions and binding have been the subject of intensive study, significantly less is understood about non-covalent interactions with carbohydrates and lipids. These interactions with macronutrients are likely to impact both the flavonoid properties in foods, such as their radical scavenging activity, and the food or beverage matrix itself, including their taste, texture and other sensorial properties. Overall, non-covalent binding of flavonoids with macronutrients is primarily driven by van der Waals interactions. From the flavonoid perspective, these interactions are modulated by characteristics such as degree of polymerization, molecular flexibility, number of external hydroxyl groups, or number of terminal galloyl groups. From the macronutrient standpoint, electrostatic and ionic interactions are generally predominant with carbohydrates, while hydrophobic interactions are generally predominant with lipids and mainly limited to interactions with flavonols. All of these interactions are involved in flavonoid-protein interactions. While primarily associated with undesirable characteristics in foods and beverages, such as astringency, negative impact on macronutrient digestibility and hazing, more recent efforts have attempted to leverage these interactions to develop controlled delivery systems or strategies to enhance flavonoids bioavailability. This paper aims at reviewing the fundamental bases for non-covalent interactions, their occurrence in food and beverage systems and their impact on the physico-chemical, organoleptic and some nutritional properties of food.

Rapid screening and identification of new soluble tannin-salivary protein aggregates in saliva by mass spectrometry (MALDI-TOF-TOF and FIA-ESI-MS)

Astringency is mainly attributed to the interaction between tannins and salivary proteins. Proline-rich proteins, histatins, and statherins are supposed to be the most reactive salivary proteins. This study aims to contribute to the knowledge of the tannin-protein binding process in saliva. It was identified for the first time in several soluble tannin-human salivary protein aggregates. A rapid mass spectrometry analytical method (MALDI-TOF and FIA-ESI-MS) was developed to identify new soluble tannin-human salivary protein aggregates. Three different tannins--procyanidin B3 (B3), procyanidin B2 gallate (B2G), and pentagalloylglucoside (PGG)--were tested to elucidate the tannin selectivity toward histatins, proline-rich proteins, and statherins in human saliva. A greater number of aggregates with a higher molecular weight was found when PGG was tested while no difference in the number and molecular mass range was observed in B3 or B2G salivary protein aggregates. This study confirms for the first time the bilateral selectivity of tannins and protein to yield soluble tannin-human salivary protein complexes. The results confirm that B3 and B2G are more selective than PGG. Furthermore, the families of proteins involved in the majority of B3-salivary protein soluble aggregates were primarly histatins, followed by basic proline-rich proteins and statherins. When B2G was tested, basic proline-rich proteins were involved in a greater number of aggregates, followed by histatines and statherins. Basic proline-rich proteins were also the family of proteins that formed a greater number of PGG-salivary protein aggregates followed by statherins and histatins. Acidic proline-rich proteins and glucosilated proline-rich proteins formed fewer soluble aggregates regardless of the tannin tested. The aggregation process was also found to be influenced by tannin and protein polarity. Indeed, the protein/tannin ratio of soluble aggregates increased with the tannin polarity. On the other hand, the only amphiphilic salivary proteins studied (histatins) formed a greater number of aggregates with the least polar tannin tested (B3).

Quantitative analysis of polymer mixtures in solution by pulsed field-gradient spin echo NMR spectroscopy

Pulsed Field-Gradient Spin Echo (PGSE) NMR, which associates to a spectral dimension the measure of diffusion coefficients, is a convenient technique for mixture analysis. Unfortunately, because of relaxation, the quantification of mixtures by PGSE NMR is far from straightforward for mixtures with strong spectral overlap. Antalek (J. Am. Chem. Soc. 128 (2006) 8402-8403) proposed a quantification strategy based on DECRA analysis and extrapolation to zero of the diffusion delay. More recently, Barrère et al. (J. Magn. Reson. 216 (2012) 201-208) presented a new strategy based also on DECRA and on the renormalization of the intensities using estimates of the T1 and T2 relaxation times. Here we report an alternative quantification approach in which the fractions are obtained by analyzing the PGSE attenuation profile with a general Stejskal-Tanner equation that explicitly includes the relaxation effects. The required values of T1 and T2 relaxation times are either independently measured with conventional sequences or determined, along with the fractions and the diffusion coefficients, from the simultaneous analysis of up to 6 PGSE data sets recorded with different diffusion delays. This method yields errors lower than 3% for the fractions, even for complete spectral overlap, as demonstrated on model binary and ternary mixtures of polystyrene in the case of a convection compensating double stimulated echo (DSTE) sequence.

Aggregation of the salivary proline-rich protein IB5 in the presence of the tannin EgCG

In the mouth, proline-rich proteins (PRP), which are major components of stimulated saliva, interact with tannins contained in food. We report in vitro interactions of the tannin epigallocatechin gallate (EgCG), with a basic salivary PRP, IB5, studied through electrospray ionization mass spectrometry (ESI-MS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). In dilute protein (IB5) solutions of low ionic strength (1 mM), the proteins repel each other, and the tannins bind to nonaggregated proteins. ESI-MS experiments determine the populations of nonaggregated proteins that have bound various numbers of tannin molecules. These populations match approximately the Poisson distribution for binding to n = 8 sites on the protein. MS/MS experiments confirm that complexes containing n = 1 to 8 EgCG molecules are dissociated with the same energy. Assuming that the 8 sites are equivalent, we calculate a binding isotherm, with a binding free energy Δμ = 7.26RT(a) (K(d) = 706 μM). In protein solutions that are more concentrated (0.21 mM) and at higher ionic strength (50 mM, pH 5.5), the tannins can bridge the proteins together. DLS experiments measure the number of proteins per aggregate. This number rises rapidly when the EgCG concentration exceeds a threshold (0.2 mM EgCG for 0.21 mM of IB5). SAXS experiments indicate that the aggregates have a core-corona structure. The core contains proteins that have bound at least 3 tannins and the corona has proteins with fewer bound tannins. These aggregates coexist with nonaggregated proteins. Increasing the tannin concentration beyond the threshold causes the transfer of proteins to the aggregates and a fast rise of the number of proteins per aggregate. A poisoned growth model explains this fast rise. Very large cationic aggregates, containing up to 10,000 proteins, are formed at tannin concentrations (2 mM) slightly above the aggregation threshold (0.2 mM).

The colloidal state of tannins impacts the nature of their interaction with proteins: the case of salivary proline-rich protein/procyanidins binding

While the definition of tannins has been historically associated with its propensity to bind proteins in a nonspecific way, it is now admitted that specific interaction also occurs. The case of the astringency perception is a good example to illustrate this phenomenon: astringency is commonly described as a tactile sensation induced by the precipitation of a complex composed of proline-rich proteins present in the human saliva and tannins present in beverages such as tea or red wines. In the present work, the interactions between a human saliva protein segment and three different procyanidins (B1, B3, and C2) were investigated at the atomic level by NMR and molecular dynamics. The data provided evidence for (i) an increase in affinity compared to shortest human saliva peptides, which is accounted for by protein "wraping around" the tannin, (ii) a specificity in the interaction below tannin critical micelle concentration (CMC) of ca. 10 mM, with an affinity scale such that C2 > B1 > B3, and (iii) a nonspecific binding above tannin CMC that conducts irremediably to the precipitation of the tannins/protein complex. Such physicochemical findings describe in accurate terms saliva protein-tannin interactions and provide support for a more subtle description by oenologists of wine astringency perception in the mouth.

The scientific exploration of saliva in the post-proteomic era: from database back to basic function

The proteome of human saliva can be considered as being essentially completed. Diagnostic markers for a number of diseases have been identified among salivary proteins and peptides, taking advantage of saliva as an easy-to-obtain biological fluid. Yet, the majority of disease markers identified so far are serum components and not intrinsic proteins produced by the salivary glands. Furthermore, despite the fact that saliva is essential for protecting the oral integuments and dentition, little progress has been made in finding risk predictors in the salivary proteome for dental caries or periodontal disease. Since salivary proteins, and in particular the attached glycans, play an important role in interactions with the microbial world, the salivary glycoproteome and other post-translational modifications of salivary proteins need to be studied. Risk markers for microbial diseases, including dental caries, are likely to be discovered among the highly glycosylated major protein species in saliva. This review will attempt to raise new ideas and also point to under-researched areas that may hold promise for future applicability in oral diagnostics and prediction of oral disease.

Investigation into the mechanism of (-)-epigallocatechin-3-gallate-induced precipitation of insulin

The molecular interactions between EGCG and insulin were investigated to probe the mechanism of EGCG-induced insulin precipitation. The results indicated that 1-5mM EGCG induced insulin into reversible globular precipitates of 185-365 nm. The formation of precipitates was facilitated at high salt concentration and pH values close to insulin's isoelectric point, indicating that hydrophobic interaction was the main driving force. The precipitation was positively related to insulin concentration, but for EGCG, there was a suitable concentration (2 mM at 2 mg/mL of insulin) at which the precipitate content reached maximum. Mass spectroscopy analysis indicated that EGCG formed clusters in the aqueous solution and the clusters correlate with the insulin precipitation. Based on extensive investigation, a physical model was proposed to explain the molecular interactions between EGCG and insulin. Namely, EGCG monomers and clusters first bound to insulin dimers via hydrophobic interaction, leading to the reduction of the thickness of the hydration layer and the partial denaturation of insulin. Then, EGCG clusters acted as bridges to induce the aggregation and precipitation of insulin.

Influence of carbohydrates on the interaction of procyanidin B3 with trypsin

The biological properties of procyanidins, in particular their inhibition of digestive enzymes, have received much attention in the past few years. Dietary carbohydrates are an environmental factor that is known to affect the interaction of procyanidins with proteins. This work aimed at understanding the effect of ionic food carbohydrates (polygalacturonic acid, arabic gum, pectin, and xanthan gum) on the interaction between procyanidins and trypsin. Physical-chemical techniques such as saturation transfer difference-NMR (STD-NMR) spectroscopy, fluorescence quenching, and nephelometry were used to evaluate the interaction process. Using STD-NMR, it was possible to identify the binding of procyanidin B3 to trypsin. The tested carbohydrates prevented the association of procyanidin B3 and trypsin by a competition mechanism in which the ionic character of carbohydrates and their ability to encapsulate procyanidins seem crucial leading to a reduction in STD signal and light scattering and to a recovery of the proteins intrinsic fluorescence. On the basis of these results, it was possible to grade the carbohydrates in their aggregation inhibition ability: XG > PA > AG ≫ PC. These effects may be relevant since the coingestion of procyanidins and ionic carbohydrates are frequent and furthermore since these might negatively affect the antinutritional properties ascribed to procyanidins in the past.

Mechanisms of tannin-induced trypsin inhibition: a molecular approach

Association of procyanidins with enzymes has drawn attention over the past few years. This work aimed to bring insights on interaction of the protease trypsin with the procyanidin dimer (B3). This interaction was characterized by fluorescence quenching, saturation transfer difference (STD) NMR, molecular modeling, and through an enzymatic inhibition assay. Further studies were conducted regarding the influence of pectin on the binding process. A general overview of the binding process may be outlined as follows: a) at low procyanidin concentrations (below the critical micellar concentration-(CMC)) a specific interaction probably driven by hydrogen bonds between the protein backbone and the procyanidin occurs and is associated with the reduction of both enzyme activity and fluorescence; b) at high procyanidin concentration (above the CMC) the interaction becomes nonspecific. This variation in both nature and extent of the interaction with the variation of procyanidin concentration shows how tannin self-association may affect the interaction between tannins and proteins. It was also shown that the mechanism through which pectin affects the interaction between procyanidin B3 and trypsin is of a competitive type.

Reactivity of human salivary proteins families toward food polyphenols

Tannins are well-known food polyphenols that interact with proteins, namely, salivary proteins. This interaction is an important factor in relation to their bioavailability and is considered the basis of several important properties of tannins, namely, the development of astringency. It has been generally accepted that astringency is due to the tannin-induced complexation and/or precipitation of salivary proline-rich proteins (PRPs) in the oral cavity. However, this complexation is thought to provide protection against dietary tannins. Neverthless, there is no concrete evidence and agreement about which PRP families (acidic, basic, and glycosylated) are responsible for the interaction with condensed tannins. In the present work, human saliva was isolated, and the proteins existing in saliva were characterized by chromatographic and proteomic approaches (HPLC-DAD, ESI-MS, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and MALDI-TOF). These approaches were also adapted to study the affinity of the different families of salivary proteins to condensed tannins by the interaction of saliva with grape seed procyanidins. The results obtained when all the main families of salivary proteins are present in a competitive assay, like in the oral cavity, demonstrate that condensed tannins interact first with acidic PRPs and statherin and thereafter with histatins, glycosylated PRPs, and bPRPs.

Wine and grape tannin interactions with salivary proteins and their impact on astringency: a review of current research

Astringency is an important characteristic of red wine quality. The sensation is generally thought to be produced by the interaction of wine tannins with salivary proteins and the subsequent aggregation and precipitation of protein-tannin complexes. The importance of wine astringency for marketability has led to a wealth of research on the causes of astringency and how tannins impact the quality of the sensation, particularly with respect to tannin structure. Ultimately, the understanding of how tannin structure impacts astringency will allow the controlled manipulation of tannins via such methods as micro-oxygenation or fining to improve the quality of wines.

J-modulation effects in DOSY experiments and their suppression: the Oneshot45 experiment

Diffusion-ordered spectroscopy (DOSY) is a powerful NMR method for identifying compounds in mixtures. DOSY experiments are very demanding of spectral quality; even small deviations from expected behaviour in NMR signals can cause significant distortions in the diffusion domain. This is a particular problem when signals overlap, so it is very important to be able to acquire clean data with as little overlap as possible. DOSY experiments all suffer to a greater or lesser extent from multiplet phase distortions caused by J-modulation, requiring a trade-off between such distortions and gradient pulse width. Multiplet distortions increase spectral overlap and may cause unexpected and misleading apparent diffusion coefficients in DOSY spectra. These effects are described here and a simple and effective remedy, the addition of a 45° purging pulse immediately before the onset of acquisition to remove the unwanted anti-phase terms, is demonstrated. As well as affording significantly cleaner results, the new method allows much longer diffusion-encoding pulses to be used without problems from J-modulation, and hence greatly increases the range of molecular sizes that can be studied for coupled spin systems. The sensitivity loss is negligible and the added phase cycling is modest. The new method is illustrated for a widely-used general purpose DOSY pulse sequence, Oneshot.

Plant polyphenols: chemical properties, biological activities, and synthesis

Eating five servings of fruits and vegetables per day! This is what is highly recommended and heavily advertised nowadays to the general public to stay fit and healthy! Drinking green tea on a regular basis, eating chocolate from time to time, as well as savoring a couple of glasses of red wine per day have been claimed to increase life expectancy even further! Why? The answer is in fact still under scientific scrutiny, but a particular class of compounds naturally occurring in fruits and vegetables is considered to be crucial for the expression of such human health benefits: the polyphenols! What are these plant products really? What are their physicochemical properties? How do they express their biological activity? Are they really valuable for disease prevention? Can they be used to develop new pharmaceutical drugs? What recent progress has been made toward their preparation by organic synthesis? This Review gives answers from a chemical perspective, summarizes the state of the art, and highlights the most significant advances in the field of polyphenol research.

Proline-rich salivary proteins have extended conformations

Three basic proline-rich salivary proteins have been produced through the recombinant route. IB5 is a small basic proline-rich protein that is involved in the binding of plant tannins in the oral cavity. II-1 is a larger protein with a closely related backbone; it is glycosylated, and it is also able to bind plant tannins. II-1 ng has the same polypeptidic backbone as II-1, but it is not glycosylated. Small angle x-ray scattering experiments on dilute solutions of these proteins confirm that they are intrinsically disordered. IB5 and II-1 ng can be described through a chain model including a persistence length and cross section. The measured radii of gyration (Rg=27.9 and 41.0+/-1 A respectively) and largest distances (rmax=110 and 155+/-10 A respectively) show that their average conformations are rather extended. The length of the statistical segment (twice the persistence length) is b=30 A, which is larger than the usual value (18 A-20 A) for unstructured polypeptide chains. These characteristics are presumably related to the presence of polyproline helices within the polypeptidic backbones. For both proteins, the radius of gyration of the chain cross-section is Rc=2.7+/-0.2A. The glycosylated protein II-1 has similar conformations but the presence of large polyoside sidegroups yields the structure of a branched macromolecule with the same hydrophobic backbone and hydrophilic branches. It is proposed that the unusually extended conformations of these proteins in solution facilitate the capture of plant tannins in the oral cavity.

Understanding the binding of procyanidins to pancreatic elastase by experimental and computational methods

Human diets are rich in secondary metabolites such as polyphenols. These compounds perform a wide range of crucial functions in biological systems and are of great interest for the pharmaceutical and food industries. In this work, the binding mode of the natural polyphenolic compounds from grape seed on the porcine pancreatic elastase surface was studied by experimental and computational methods. Fluorescence quenching, circular dichroism, nephelometry, dynamic light scattering (DLS), molecular docking, and molecular dynamics simulation studies were performed. A decrease in fluorescence intensities was observed with addition of increasing polyphenol concentrations. The order of binding ability obtained was oligomeric fraction of procyanidins (OFP) > tetramer > trimer > dimer B3 procyanidins. Thus a relationship between higher molecular weight and binding ability was observed. The interaction between these molecules and the enzyme occurs by a static mechanism, as inferred from the high apparent fluorescence and bimolecular quenching constants. A blue shift in the maximal emission wavelength could be seen, which indicates that the tryptophan residues acquire a more hydrophobic character upon procyanidin binding. Molecular docking and dynamics simulations also demonstrate that the SASA (solvent-accessible surface area) values of tryptophans decrease with the binding of these compounds, preventing the accessibility of water molecules, which agrees with the referred blue shift. Circular dichroism studies indicate a decrease in alpha-helix content, followed by an increase in the beta-sheet component of secondary structures of this enzyme. DLS and nephelometry techniques also indicate a relationship between large procyanidins and aggregate formation ability.

Prediction of Xaa-Pro peptide bond conformation from sequence and chemical shifts

We present a program, named Promega, to predict the Xaa-Pro peptide bond conformation on the basis of backbone chemical shifts and the amino acid sequence. Using a chemical shift database of proteins of known structure together with the PDB-extracted amino acid preference of cis Xaa-Pro peptide bonds, a cis/trans probability score is calculated from the backbone and (13)C(beta) chemical shifts of the proline and its neighboring residues. For an arbitrary number of input chemical shifts, which may include Pro-(13)C(gamma), Promega calculates the statistical probability that a Xaa-Pro peptide bond is cis. Besides its potential as a validation tool, Promega is particularly useful for studies of larger proteins where Pro-(13)C(gamma) assignments can be challenging, and for on-going efforts to determine protein structures exclusively on the basis of backbone and (13)C(beta) chemical shifts.