Identification of Structural Features of Condensed Tannins That Affect Protein Aggregation

Abstract

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.

Chestnut extract but not sodium salicylate decrease the severity of diarrhea and enterotoxigenic Escherichia coli F4 shedding in artificially infected piglets

“…Nevertheless, besides a positive effect of tannins on reducing diarrhea, previous experiments have failed to show a positive effect of tannins on ETEC shedding [15, 28]. The lack of effects of tannins observed in previous studies is probably related to differences in the bioactivity of tannins according to the dose (1% CE, as previously administered, was not sufficiently high compared to 2% in the present study), as well as to the chemical structure of tannins [32]. However, caution should be taken in using hydrolysable tannins in experiments because up to now, it has been unclear whether the effects of tannins are due to the hydrolysable tannins and/or to their metabolites (ellagic acid and urolithins), as hydrolysable tannins can be hydrolyzed both in the stomach and the gut [33].…”

Activity, Purification, and Analysis of Condensed Tannins: Current State of Affairs and Future Endeavors

“…In related studies, the DP of CTs has been shown to parallel enzyme inhibition of trypsin, a-amylase and lipase (Horigome et al, 1988) and trypsin (Helsper et al, 1993). Similar decreases in the a-helical/b sheets ratios were observed during the formation of CT-protein complexes of bovine serum albumin (BSA) with a collection of compositionally different CTs (Ropiak et al, 2017). Interestingly, additional studies have shown CT binding to increase the proportion of b sheet at the expense of the a-helical content in the CT-protein complex.…”

“…Examination of the complexation of pancreatic elastase with CT from grape seed (dimer through tetramer CT and an isolated oligomeric fraction of CT) via circular dichroism reveals a decrease in percentage a-helical content with a concomitant increase in percentage b sheet content (Brás et al, 2010). Similar decreases in the a-helical/b sheets ratios were observed during the formation of CT-protein complexes of bovine serum albumin (BSA) with a collection of compositionally different CTs (Ropiak et al, 2017).…”

“…For >40 yr, publications have listed examples of CTs of similar composition but varying in DP or mDP, demonstrating that larger CTs are more potent protein-precipitating entities (Haslam, 1974;Jones et al, 1976;Porter and Woodruffe, 1984;Kumar and Horigome, 1986;Ezaki-Furuichi et al, 1987;Horigome et al, 1988;Ricardo-da-Silva et al, 1991: Helsper et al, 1993: Baxter et al, 1997Osborne and McNeill, 2001;Brás et al, 2010;Huang et al, 2011;Harbertson et al, 2014;Saminathan et al, 2014;Zeller et al, 2015b;Kilmister et al, 2016). The mDP and average molecular weight of CTs have even been claimed to override effect of galloylation and the presence of A-type linkages (Ropiak et al, 2017). In related studies, the DP of CTs has been shown to parallel enzyme inhibition of trypsin, a-amylase and lipase (Horigome et al, 1988) and trypsin (Helsper et al, 1993).…”

“…Hagerman et al (1998) showed that a heptadecamer (containing 17 linked flavan-3-ol subunits) CT polymer exhibited this type of protein-CT-protein crosslinking. Recent research studies (Kilmister et al, 2016;Ropiak et al, 2017) indicate that CTs whose size is seven or more flavan-3-ol subunits are capable of noncovalent cross-linking, promote protein aggregation, and accelerate formation of insoluble CT-protein complexes, leading to precipitation. As an example of the smallest "CT" entity to promote cross-linking, an X-ray crystal structure involving the monomer flavan-3-ol epigallocatechin gallate shows that this monoflavan-3-ol bridges two transthyretin protein molecules, stabilizing the complex enough for crystal formation (Miyata et al, 2010).…”