The complexity of condensed tannin binding to bovine serum albumin – An isothermal titration calorimetry study

Exploring the Interactions between Plant Proanthocyanidins and Thiabendazole: Insights from Isothermal Titration Calorimetry

Anthelmintic resistance in gastrointestinal nematodes produces substantial challenges to agriculture, and new strategies for nematode control in livestock animals are called for. Natural compounds, including tannins, with proven anthelmintic activity could be a functional option as structurally diverse complementary compounds to be used alongside commercial anthelmintics. However, the dual use of two anthelmintic components requires an understanding of the pharmacological effects of the combination, while information concerning the interactions between plant-based polyphenols and commercial anthelmintics is scarce. We studied the direct interactions of proanthocyanidins (PAs, syn. condensed tannins) and a commercial anthelmintic thiabendazole, as a model substance of benzimidazoles, by isothermal titration calorimetry (ITC). Our results show evidence of a direct interaction of an exothermic nature with observed enthalpy changes ranging from 0 to -30 kJ/mol. The strength of the interaction between PAs and thiabendazole is mediated by structural characteristics of the PAs with the strongest positive correlation originating from the presence of galloyl groups and the increased degree of polymerization.

The Impact of Dehulling and Germination on the Physiochemical, Protein Solubility and Water and Oil Holding Capacities of Yellow Eye Bean (Phaseolus vulgaris L.) Protein Concentrates

Pulse varieties including Yellow Eye (YE) beans (Phaseolus vulgaris L.) are a rich source of protein (~26.5%) that can be utilized to create value-added protein concentrates. Pre-treatments including dehulling and germination have been shown to be effective at improving the nutritional and functional properties of extracted protein concentrates. However, the composition and functionality of these protein concentrates can vary depending on the pre-treatments and the method of extraction used (salt vs. alkaline). Furthermore, little is known about the impact of combining these different processing methods on the properties of YE bean protein concentrates. The objective of this study was to evaluate how germination and dehulling pre-treatments individually and when combined influence protein extraction efficiency, physiochemical properties (surface hydrophobicity and intrinsic fluorescence), and the functionality (solubility, oil and water holding capacities) of salt and alkaline extracted protein concentrates. Compared to the salt extracted concentrates, the alkaline protein concentrates exhibited higher protein recovery yields (16–23% vs. 43–56%) respectively. Conversely, the salt extracted protein concentrates exhibited superior functional properties as observed by improved water holding capacities and less variation in their solubilities at different pH values (4 to 10). When the pre-treatments were combined, the salt extracted concentrates exhibited improved extraction efficiencies and improved hydrophobicity and intrinsic fluorescence, whereas the opposite trend was observed in the alkaline protein concentrates. These observations were attributed to differences in the protein content and composition of the salt vs. alkaline protein concentrates. Overall, these findings suggest that dehulling and germination are potential processing methods that may be used to improve the physiochemical characteristics of salt extracted protein concentrates from yellow eye beans. Future research may investigate the potential application of these ingredients in different food formulations.

Lentil Protein and Tannic Acid Interaction Limits in Vitro Peptic Hydrolysis and Alters Peptidomic Profiles of the Proteins

In this study, the nature of lentil protein-tannic acid (LPTA) interaction and its effect on in vitro pepsin digestion were investigated. LPTA mixtures containing 1% w/v LP and 0.001-0.5% TA were prepared and characterized in terms of particle size, thermal properties, and secondary and tertiary structures. A 20-fold increase in particle size was observed in LPTA0.5% compared to LP control (without TA), indicating aggregation. Static quenching of tryptophan residues within the protein hydrophobic folds was observed. Increasing TA levels also enhanced protein thermal stability. Over 50% reduction in free amino groups of LPTA 0.5%, relative to LP, was observed after pepsin digestion. Cleavage specificity of pepsin and peptidomic profile of LP were modified by the presence of TA in LPTA 0.5%. This study showed that 0.5% w/v TA induced protein aggregation and reduced LP digestibility by hindering the accessibility of pepsin to the protein network, thus modifying the profile of released peptides.

Interactions between Hydrolysable Tannins and Lipid Vesicles from Escherichia coli with Isothermal Titration Calorimetry

Isothermal titration calorimetry (ITC) was used to study the interactions between hydrolysable tannins (HTs) and lipid vesicles prepared from a phospholipid extract of Escherichia coli (E. coli). A group of 24 structurally different HTs was selected, and structural differences affecting their affinities to interact with lipid vesicles in aqueous buffered media were identified. In general, the interactions between HTs and lipid vesicles were exothermic in nature, and ITC as a technique functioned well in the screening of HTs for their affinity for lipids. Most notably, the galloyl moiety, the structural flexibility of the entire tannin structure, the hydrophobicity of the tannin, and higher molecular weight were observed to be important for the stronger interactions with the lipids. The strongest interactions with lipids were observed for rugosins D and G. It was also observed that some HTs with moderate hydrophobicities, such as geraniin, chebulagic acid, and chebulinic acid, did not have any detectable interactions with the lipid vesicles, suggesting that a hydrophobic structure alone does not guarantee an affinity for lipids.

Bioactive compounds: Application of albumin nanocarriers as delivery systems

Enriched products with bioactive compounds (BCs) show the capacity to produce a wide range of possible health effects. Most BCs are essentially hydrophobic and sensitive to environmental factors; so, encapsulation becomes a strategy to solve these problems. Many globular proteins have the intrinsic ability to bind, protect, encapsulate, and introduce BCs into nutraceutical or pharmaceutical matrices. Among them, albumins as human serum albumin (HSA), bovine serum albumin (BSA), ovalbumin (OVA) and α-lactalbumin (ALA) are widely abundant, available, and applied in many industrial sectors, becoming promissory materials to encapsulate BCs. Therefore, this review focuses on researches about the main groups of natural origin BCs (namely phenolic compounds, lipids, vitamins, and carotenoids), the different types of nanostructures based on albumins to encapsulate them and the main fields of application for BCs-loaded albumin systems. In this context, phenolic compounds (catechins, quercetin, and chrysin) are the most extensively BCs studied and encapsulated in albumin-based nanocarriers. Other extensively studied subgroups are stilbenes and curcuminoids. Regarding lipids and vitamins; terpenes, carotenoids (β-carotene), and xanthophylls (astaxanthin) are the most considered. The main application areas of BCs are related to their antitumor, anti-inflammatory, and antioxidant properties. Finally, BSA is the most used albumin to produced BCs-loaded nanocarriers.

The influence of intrinsic and extrinsic factors on protein-polyphenol interactions in dairy systems

The application of polyphenols in dairy products is becoming more widespread due to the rich protein content of dairy products reacting with polyphenols. Many studies have pointed to the positive effects of polyphenol-protein binding on dairy products. This article illustrated the mechanisms of how polyphenols react with proteins. The effects of the combination of the polyphenols and protein were described in terms of intrinsic and extrinsic factors, as well as the effects on food properties. Moreover, specific examples of the use of polyphenols in dairy products will also be proposed. Importantly, based on the reported findings, future processes that exploit and develop this interaction can be considered to enable the targeting of polyphenols and proteins in dairy products to secure a range of industrial benefits.

Reynoutria Rhizomes as a Natural Source of SARS-CoV-2 Mpro Inhibitors-Molecular Docking and In Vitro Study

More than a year has passed since the world began to fight the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for the Coronavirus disease 2019 (COVID-19) pandemic, and still it spreads around the world, mutating at the same time. One of the sources of compounds with potential antiviral activity is Traditional Chinese Medicinal (TCM) plants used in China in the supportive treatment of COVID-19. Reynoutria japonica is important part of the Shu Feng Jie Du Granule/Capsule-TCM herbal formula, recommended by China Food and Drug Administration (CFDA) for treatment of patients with H1N1- and H5N9-induced acute lung injury and is also used in China to treat COVID-19, mainly combined with other remedies. In our study, 25 compounds from rhizomes of R. japonica and Reynoutria sachalinensis (related species), were docked into the binding site of SARS-CoV-2 main protease. Next, 11 of them (vanicoside A, vanicoside B, resveratrol, piceid, emodin, epicatechin, epicatechin gallate, epigallocatechin gallate, procyanidin B2, procyanidin C1, procyanidin B2 3,3'-di-O-gallate) as well as extracts and fractions from rhizomes of R. japonica and R. sachalinensis were tested in vitro using a fluorescent peptide substrate. Among the tested phytochemicals the best results were achieved for vanicoside A and vanicoside B with moderate inhibition of SARS-CoV-2 Mpro, IC50 = 23.10 µM and 43.59 µM, respectively. The butanol fractions of plants showed the strongest inhibition of SARS-CoV-2 Mpro (IC50 = 4.031 µg/mL for R. sachalinensis and IC50 = 7.877 µg/mL for R. japonica). As the main constituents of butanol fractions, besides the phenylpropanoid disaccharide esters (e.g., vanicosides), are highly polymerized procyanidins, we suppose that they could be responsible for their strong inhibitory properties. As inhibition of SARS-CoV-2 main protease could prevent the replication of the virus our research provides data that may explain the beneficial effects of R. japonica on COVID-19 and identify the most active compounds worthy of more extensive research.

Applications of isothermal titration calorimetry in pure and applied research from 2016 to 2020

The last 5 years have seen a series of advances in the application of isothermal titration microcalorimetry (ITC) and interpretation of ITC data. ITC has played an invaluable role in understanding multiprotein complex formation including proteolysis-targeting chimeras (PROTACS), and mitochondrial autophagy receptor Nix interaction with LC3 and GABARAP. It has also helped elucidate complex allosteric communication in protein complexes like trp RNA-binding attenuation protein (TRAP) complex. Advances in kinetics analysis have enabled the calculation of kinetic rate constants from pre-existing ITC data sets. Diverse strategies have also been developed to study enzyme kinetics and enzyme-inhibitor interactions. ITC has also been applied to study small molecule solvent and solute interactions involved in extraction, separation, and purification applications including liquid-liquid separation and extractive distillation. Diverse applications of ITC have been developed from the analysis of protein instability at different temperatures, determination of enzyme kinetics in suspensions of living cells to the adsorption of uremic toxins from aqueous streams.

Phenolic Compounds of Reynoutria sp. as Modulators of Oral Cavity Lactoperoxidase System

Lactoperoxidase (LPO) together with its (pseudo)halogenation cycle substrates, H₂O₂ and thiocyanate ions oxidized to hypothiocyanite ions, form one of the main systems involved in antimicrobial defense within the oral cavity. In bacterial diseases such as dental caries, lactoperoxidase is oxidized to a form known as Compound II, which is characterized by its inability to oxidize SCN^–, resulting in a decreased generation of antimicrobial products. Reynoutria sp. rizome extracts, due to their high polyphenol content, have been tested as a source of compounds able to regenerate the antimicrobial activity of lactoperoxidase through converting the Compound II to the native LPO state. In the presented study, acetone extracts of R. japonica, R. sachalinensis, and R. x bohemica, together with their five fractions and four selected polyphenols dominating in the studied in extracts, were tested toward lactoperoxidase reactivating potential. For this purpose, IC50, EC50, and activation percentage were determined by Ellman’s method. Furthermore, the rate constants for the conversion of Compound I–Compound II and Compound II–native-LPO in the presence of extracts, extracts fractions, and selected polyphenols were determined. Finally, the ability to enhance the antimicrobial properties of the lactoperoxidase system was tested against Streptococcus mutans. We proved that Reynoutria sp. rhizome is the source of lactoperoxidase peroxidation cycle substrates, which can act as activators and inhibitors of the antimicrobial properties of that system. The presented study shows that the reactivation of lactoperoxidase could become a potential therapeutic target in prevention and treatment support in some infectious oral diseases.

Distribution of Protein Precipitation Capacity within Variable Proanthocyanidin Fingerprints

Proanthocyanidins (PAs) are highly bioactive plant specialized metabolites. One of their most characteristic features is their ability to precipitate proteins. In this study, eleven plant species were used to study the structure–activity patterns between PAs and their protein precipitation capacity (PPC) with bovine serum albumin. To obtain a comprehensive selection of PAs with highly variable procyanidin to prodelphinidin ratios and mean degree of polymerizations, nearly 350 subfractions were produced from the eleven plant species by semi-preparative liquid chromatography. Their PA composition was defined by tandem mass spectrometry and high-resolution mass spectrometry, and their PPC was measured with a turbidimetry-based well-plate reader assay. The distribution of the PPC within plant species varied significantly. The mean degree of polymerization of the PAs had a strong correlation with the PPC (r = 0.79). The other structural features were significant from the PPC point of view as well, but they contributed to the PPC in different ways in different plant species. Retention time, prodelphinidin proportion, and mean degree of polymerization explained 64% of the measured variance of the PPC.

Comparison of Protein Precipitation Ability of Structurally Diverse Procyanidin-Rich Condensed Tannins in Two Buffer Systems

The protein precipitation (PP) of bovine serum albumin (BSA), lysozyme (LYS), and alfalfa leaf protein (ALF) by four procyanidin-rich condensed tannin (CT) samples in both 2-[N-morpholino]ethanesulfonic acid (MES) and a modified Goering-Van Soest (GVS) buffer is described. Purified CT samples examined included Vitis vinifera seed (mean degree of polymerization [mDP] 4.1, 16.5% galloylated), Tilia sp. flowers (B-type linkages, mDP 5.9), Vaccinium macrocarpon berries (mDP 8.7, 31.7% A-type linkages). and Trifolium pratense flowers (B-type linkages, mDP 12.3) and were characterized by 2D NMR (>90% purity). In general, CTs precipitated ALF > LYS ≥ BSA. PP in GVS buffer was 1 to 2.25 times greater than that in MES buffer (25 °C). The GVS buffer system better reflects the results/conclusions from the literature on the impacts mDP, galloylation, and A-type linkages have on PP. Determinations of PP using the MES buffer at 37 °C indicated that some of these differences may be attributed to the temperature at which GVS buffer determinations are conducted. In vitro PP studies using the GVS buffer may offer better guidance when selecting CT-containing forages and amendments for ruminant feeding studies.

Ellagitannins with Glucopyranose Cores Have Higher Affinities to Proteins than Acyclic Ellagitannins by Isothermal Titration Calorimetry

The thermodynamics of the interactions of different ellagitannins with two proteins, namely, bovine serum albumin (BSA) and gelatin, were studied by isothermal titration calorimetry. Twelve individual ellagitannins, including different monomers, dimers, and a trimer, were used. The studies showed that several structural features affected the interaction between the ellagitannin and the protein. The interactions of ellagitannins with proteins were stronger with gelatin than with BSA. The ellagitannin-gelatin interactions contained both the primary stronger and the secondary weaker binding sites. The ellagitannin-BSA interactions showed very weak secondary interactions. The ellagitannins with glucopyranose cores had stronger interaction than C-glycosidic ellagitannins with both proteins. In addition, the observed enthalpy change increased as the degree of oligomerization increased. The stronger interactions were also observed with free galloyl groups in the ellagitannin structure and with higher molecular flexibility. Other smaller structural features did not show any overall trend.

Unravelling the interaction mechanism between clioquinol and bovine serum albumin by multi-spectroscopic and molecular docking approaches

Clioquinol has recently been proposed for the treatment of Alzheimer's disease. It is able to diminish β-amyloid protein aggregation and to restore cognition of Alzheimer's mice. However, its therapeutic benefits for Alzheimer's disease in human remain controversy and need further confirmation. Herein, we have explored the interaction mechanism of clioquinol toward bovine serum albumin (BSA) by means of multi-spectroscopic and docking simulation approaches. Clioquinol interacts with BSA by a combined mechanism of static and dynamic processes. Application of the Hill's equation to fluorescence quenching experiment revealed that the binding constant of the BSA-clioquinol complex is extremely high at 10⁸ M^-1 level. Competitive displacement and docking analysis consistently suggested that there are the multiple binding modes of clioquinol toward BSA. Competitive binding study showed that clioquinol shares the binding sites with ibuprofen and digitoxin on albumin, referring to be site II and site III binding compounds. Besides, partial binding in site I was also observed. Docking simulation confirmed that clioquinol favors to bind in site I, site II, site III, fatty acid binding site 5, and the protein cleft between subdomain IB and IIIB of the BSA. Due to its small size and electric dipole property, clioquinol may easily fit in multiple pockets of the BSA. Our finding suggests the potential role of BSA as a clioquinol carrier in the vascular system. Nonetheless, clioquinol-induced BSA aggregation has been observed by the three-dimensional fluorescence technique. This phenomenon may not only impair the BSA, but may also affect other endogenous proteins, which eventually causes adverse effects to human. Therefore, the redesigned or modified molecular structure of clioquinol may reduce its toxicity and improve its bioavailability.

Screening Naturally Occurring Phenolic Antioxidants for Their Suitability as Additives to CHO Cell Culture Media Used to Produce Monoclonal Antibodies

This study identified several antioxidants that could be used in Chinese hamster ovary (CHO)cell culture media and benefit monoclonal antibody production. The flavan-3-ols, catechin, epicatechin, epigallocatechin gallate and gallocatechin gallate all had no detrimental effect on cell viability at the concentrations tested, and they reduced the final viable cell count with a resulting rise in the cell specific productivity. The flavone, luteolin behave similarly to the flavan-3-ols. Resveratrol at 50 μM concentration resulted in the most pronounced reduction in viable cell density with minimal decrease in IgG synthesis and the largest increase in cell specific productivity. Low concentrations of α-tocopherol (35 μM) reduced viable cell density and raised cell specific productivity, but at higher concentration it had little additional effect. As high concentrations of α-tocopherol are not toxic to CHO cells, its addition as an anti-oxidant has great potential. Kaempferol up to 50 μM, curcumin up to 20 μM and piceid up to 100 μM showed little effect on growth or IgG synthesis and could be useful as antioxidants. Caffeic acid phenethyl ester was toxic to CHO cell and of no interest. Seven of the phenolic compounds tested are potential cell cycle inhibitors as well as having intrinsic antioxidant properties.

Proanthocyanidins: A comprehensive review

Proanthocyanidins are condensed tannins with various pharmacological properties. These phytochemicals are considered as 'offense and defense molecules because of their human health benefits. The validation of their diverse health aspects, namely, antioxidant, anticancer, antidiabetic, neuroprotective, and antimicrobial has earned them repute in thermochemistry. Proanthocyanidins are oligo- or polymers of monomeric flavan-3-ols produced as an end product of flavonoid biosynthetic pathway. Agricultural wastes and food processing wastes contain immense amount of proanthocyanidins, exploitation of which can be a sustainable source of dietary supplements and functional ingredients. The current review article discusses recent developments in the health promoting properties of proanthocyanidins and the associated hurdles.

Studies on the activation of isocitrate dehydrogenase kinase/phosphatase (AceK) by Mn2+ and Mg2

Isocitrate dehydrogenase kinase/phosphatase (AceK) is a bifunctional enzyme with both kinase and phosphatase activities that are activated by Mg²⁺. We have studied the interactions of Mn²⁺and Mg²⁺ with AceK using isothermal titration calorimetry (ITC) combined with molecular docking simulations and show for the first time that Mn²⁺ also activates the enzyme activities. However, Mn²⁺ and Mg²⁺ exert their effects by different mechanisms. Although they have similar binding constants (of 1.11 × 10⁵ and 0.98 × 10⁵ M^-1, respectively) for AceK and induce conformational changes of the enzyme, they do not compete for the same binding site. Instead Mn²⁺ appears to bind to the regulatory domain of AceK, and its effect is transmitted to the active site of the enzyme by the conformational change that it induces. The information in this study should be very useful for understanding the molecular mechanism underlying the interaction between AceK and metal ions, especially Mn²⁺ and Mg²⁺.

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.

Effect of heating and ionic strength on the interaction of bovine serum albumin and the antinutrients tannic and phytic acids, and its influence on in vitro protein digestibility

Bioavailability of food nutrients can be reduced in the presence of antinutrients such as phytates and tannins. This work aimed to study bovine serum albumin binding to phytic acid and tannic acid, and its influence on in vitro protein digestibility. The effect of autoclaving and boiling on protein digestibility and the microstructure of complexes was also evaluated. Results showed that high ionic strength promotes greater affinity between tannic acid and bovine serum albumin, and decreases in vitro protein digestibility. For phytic acid and bovine serum albumin, the opposite behavior is observed because interactions are governed by electrostatic forces. A rise in temperature above that causing denaturation of the protein favors its interaction with phytic acid, and disfavors that with tannic acid, probably due to different protein binding site exposure. For both antinutrients, heating treatment increased protein hydrolysis, the size of complexes and their fragility.

Interaction mechanisms of condensed tannins (proanthocyanidins) with wheat gluten proteins

Proanthocyanidins (PA) crosslink wheat gluten, increasing its polymer size and strength. However, mechanisms behind these interactions are unknown. This study used PA of different MW profiles (mean degree of polymerization 8.3 and 19.5) to investigate how PA polymerize gluten. The higher MW PA had greater binding affinity for both glutenins and gliadins than lower MW PA, whereas both PA precipitated glutenins more efficiently than gliadins. The PA preferentially bound the largest of the protein fractions available: high MW glutenin subunits (HMW-GS) over low MW-GS, and ω-gliadins over α- and γ-gliadins. Furthermore, within the HMW-GS, PA bound more of the larger x-type than the smaller y-type. Proanthocyanidins reduced gluten solubility in urea and decreased surface hydrophobicity of glutenins, but not gliadins. The PA appear to preferentially crosslink HMW-GS via hydrophobic interactions and hydrogen bonding, whereas their interaction with gliadins is dominated by hydrogen bonding and is relatively weaker.

Resolubilization of Protein from Water-Insoluble Phlorotannin-Protein Complexes upon Acidification

Marine phlorotannins (PhT) from Laminaria digitata might protect feed proteins from ruminal digestion by formation of insoluble non-covalent tannin-protein complexes at rumen pH (6-7). Formation and disintegration of PhT-protein complexes was studied with β-casein (random coil) and bovine serum albumin (BSA, globular) at various pH. PhT had similar binding affinity for β-casein and BSA as pentagalloyl glucose, as studied by fluorescence quenching. The affinity of PhT for both proteins was independent of pH (3.0, 6.0, and 8.0). In the presence of PhT, the pH range for precipitation of tannin-protein complexes widened to 0.5-1.5 pH units around the isoelectric point (pI) of the protein. Complete protein resolubilization from insoluble PhT-protein complexes was achieved at pH 7 and 2 for β-casein and BSA, respectively. It was demonstrated that PhT modulate the solubility of proteins at neutral pH and that resolubilization of PhT-protein complexes at pH deviating from pI is mainly governed by the charge state of the protein.

Molecular Approach to the Synergistic Effect on Astringency Elicited by Mixtures of Flavanols

The interactions between salivary proteins and wine flavanols (catechin, epicatechin, and mixtures thereof) have been studied by HPLC-DAD, isothermal titration microcalorimetry, and molecular dynamics simulations. Chromatographic results suggest that the presence of these flavanol mixtures could facilitate the formation of precipitates to the detriment of soluble aggregates. Comparison between the thermodynamic parameters obtained showed remarkably higher negative values of ΔG in the system containing the mixture of both flavanols in comparison to the systems containing individual flavanols, indicating a more favorable scenario in the mixing system. Also, the apparent binding constants were higher in this system. Furthermore, molecular dynamics simulations suggested a faster and greater cooperative binding of catechin and epicatechin to IB7₁₄ peptides when both types of flavanols are present simultaneously in solution.

Identification of Structural Features of Condensed Tannins That Affect Protein Aggregation

A diverse panel of condensed tannins was used to resolve the confounding effects of size and subunit composition seen previously in tannin-protein interactions. Turbidimetry revealed that size in terms of mean degree of polymerisation (mDP) or average molecular weight (amw) was the most important tannin parameter. The smallest tannin with the relatively largest effect on protein aggregation had an mDP of ~7. The average size was significantly correlated with aggregation of bovine serum albumin, BSA (mDP: r = -0.916; amw: r = -0.925; p<0.01; df = 27), and gelatin (mDP: r = -0.961; amw: r = -0.981; p<0.01; df = 12). The procyanidin/prodelphinidin and cis-/trans-flavan-3-ol ratios gave no significant correlations. Tryptophan fluorescence quenching indicated that procyanidins and cis-flavan-3-ol units contributed most to the tannin interactions on the BSA surface and in the hydrophobic binding pocket (r = 0.677; p<0.05; df = 9 and r = 0.887; p<0.01; df = 9, respectively). Circular dichroism revealed that higher proportions of prodelphinidins decreased the apparent α-helix content (r = -0.941; p<0.01; df = 5) and increased the apparent β-sheet content (r = 0.916; p<0.05; df = 5) of BSA.

Relationship of Soluble Grape-Derived Proteins to Condensed Tannin Extractability during Red Wine Fermentation

In red winemaking, the extractability of condensed tannins (CT) can vary considerably even under identical fermentation conditions, and several explanations for this phenomenon have been proposed. Recent work has demonstrated that grape pathogenesis-related proteins (PRPs) may limit retention of CT added to finished wines, but their relevance to CT extractability has not been evaluated. In this work, Vitis vinifera and interspecific hybrids (Vitis ssp.) from both hot and cool climates were vinified under small-scale, controlled conditions. The final CT concentration in wine was well modeled from initial grape tannin and juice protein concentrations using the Freundlich equation (r²= 0.686). In follow-up experiments, separation and pretreatment of juice by bentonite, heating, freezing, or exogenous tannin addition reduced protein concentrations in juices from two grape varieties. The bentonite treatment also led to greater wine CT for one of the varieties, indicating that prefermentation removal of grape protein may be a viable approach to increasing wine CT.

Interactions Between Nutrition and Infections With Haemonchus contortus and Related Gastrointestinal Nematodes in Small Ruminants

Interactions between host nutrition and feeding behaviour are central to understanding the pathophysiological consequences of infections of the digestive tract with parasitic nematodes. The manipulation of host nutrition provides useful options to control gastrointestinal nematodes as a component of an integrated strategy. Focussed mainly on the Haemonchus contortus infection model in small ruminants, this chapter (1) illustrates the relationship between quantitative (macro- and micro-nutrients) and qualitative (plant secondary metabolites) aspects of host nutrition and nematode infection, and (2) shows how basic studies aimed at addressing some generic questions can help to provide solutions, despite the considerable diversity of epidemiological situations and breeding systems.

Interactions of grape tannins and wine polyphenols with a yeast protein extract, mannoproteins and β-glucan

At present, there is a great interest in enology for yeast derived products to replace aging on lees in winemaking or as an alternative for wine fining. These are yeast protein extracts (YPE), cell walls and mannoproteins. Our aim was to further understand the mechanisms that drive interactions between these components and red wine polyphenols. To this end, interactions between grape skin tannins or wine polyphenols or tannins and a YPE, a mannoprotein fraction and a β-glucan were monitored by binding experiments, ITC and DLS. Depending on the tannin structure, a different affinity between the polyphenols and the YPE was observed, as well as differences in the stability of the aggregates. This was attributed to the mean degree of polymerization of tannins in the polyphenol fractions and to chemical changes that occur during winemaking. Much lower affinities were found between polyphenols and polysaccharides, with different behaviors between mannoproteins and β-glucans.

Pathogenesis-Related Proteins Limit the Retention of Condensed Tannin Additions to Red Wines

Exogenous additions of condensed tannin (CT) to must or wine are a common winemaking practice, but many studies have reported inexplicably low and variable retention of added CT. We observed that additions of purified CT to red wines can result in the formation of an insoluble precipitate with high nitrogen content. Proteomic analysis of the precipitant identified several classes of pathogenesis-related proteins. Proteins in juices and red wines were quantitated by SDS-PAGE and were highest in native Vitis spp., followed by interspecific hybrids and Vitis vinifera. Wine protein was positively correlated with the ratio of juice protein to the quantity of tannin derived from fruit. The binding of added CT by wine protein could be well modeled by the Freundlich equation. These observations may explain the poor CT retention in previous studies, particularly for interspecific hybrids, and also indicate that protein removal during winemaking may improve exogenous CT retention.

Binding of an Oligomeric Ellagitannin Series to Bovine Serum Albumin (BSA): Analysis by Isothermal Titration Calorimetry (ITC)

A unique series of oligomeric ellagitannins was used to study their interactions with bovine serum albumin (BSA) by isothermal titration calorimetry. Oligomeric ellagitannins, ranging from monomer to heptamer and a mixture of octamer-undecamers, were isolated as individual pure compounds. This series allowed studying the effects of oligomer size and other structural features. The monomeric to trimeric ellagitannins deviated most from the overall trends. The interactions of ellagitannin oligomers from tetramers to octa-undecamers with BSA revealed strong similarities. In contrast to the equilibrium binding constant, enthalpy showed an increasing trend from the dimer to larger oligomers. It is likely that first the macrocyclic part of the ellagitannin binds to the defined binding sites on the protein surface and then the "flexible tail" of the ellagitannin coats the protein surface. The results highlight the importance of molecular flexibility to maximize binding between the ellagitannin and protein surfaces.

Structure Activity Related, Mechanistic, and Modeling Studies of Gallotannins containing a Glucitol-Core and α-Glucosidase

Gallotannins containing a glucitol core, which are only produced by members of the maple (Acer) genus, are more potent α-glucosidase inhibitors than the clinical drug, acarbose. While this activity is influenced by the number of substituents on the glucitol core (e.g. more galloyl groups leads to increased activity), the mechanisms of inhibitory action are not known. Herein, we investigated ligand-enzyme interactions and binding mechanisms of a series of 'glucitol-core containing gallotannins (GCGs)' against the α-glucosidase enzyme. The GCGs included ginnalins A, B and C (containing two, one, and one galloyl/s, respectively), maplexin F (containing 3 galloyls) and maplexin J (containing 4 galloyls). All of the GCGs were noncompetitive inhibitors of α-glucosidase and their interactions with the enzyme were further explored using biophysical and spectroscopic measurements. Thermodynamic parameters (by isothermal titration calorimetry) revealed a 1:1 binding ratio between GCGs and α-glucosidase. The binding regions between the GCGs and α-glucosidase, probed by a fluorescent tag, 1,1'-bis(4-anilino-5-napththalenesulfonic acid, revealed that the GCGs decreased the hydrophobic surface of the enzyme. In addition, circular dichroism analyses showed that the GCGs bind to α-glucosidase and lead to loss of the secondary α-helix structure of the protein. Also, molecular modeling was used to predict the binding site between the GCGs and the α-glucosidase enzyme. This is the first study to evaluate the mechanisms of inhibitory activities of gallotannins containing a glucitol core on α-glucosidase.