Digestion Resistance of Soybean 7S Protein and Its Implications for Reinforcing the Gastric Mucus Barrier

Abstract

Previous studies have found that soybean protein, especially soybean 7S protein (β-conglycinin), exhibits digestion resistance, but the mechanism of digestion resistance and its implications for human health are still unclear. Here, we show that the extracted soybean 7S protein contains both oligomer globulins and amyloid aggregates, while the gastric digested soybean 7S protein only contains amyloid aggregates and thus exhibits digestion resistance. An animal experiment shows that un-digestible soybean 7S protein effectively prevents aspirin-induced acute gastric mucosa damage. The impacts of un-digestible soybean 7S protein on gastric mucus barrier properties are investigated using quartz crystal microbalance with dissipation (QCM-D), Langmuir monolayer, and multiple particle tracking (MPT). Results show that these un-digestible protein aggregates can penetrate into gastric mucus, increase the viscosity and compactness of the mucin layer, and reinforce the gastric mucus barrier properties. The findings are helpful to understand that high consumption of non-fermented soybean foods is associated with a decreased risk of gastric cancer.

Bile Acid Profile Influences Digestion Resistance and Antigenicity of Soybean 7S Protein

“…To visualize the unfolding of protein amyloid aggregates by model bile, the fluorescence probe ThT was used to detect the cross-β sheet structure in amyloid aggregates or fibrils Figure b shows CLSM images of the ThT-stained gastric digests of soybean 7S protein and found that ThT binds to protein with high fluorescence intensity (green dots), confirming the structural characteristics of amyloid aggregates . Upon increasing the concentration of model bile, the overall trend of decreased ThT fluorescence intensity is observed, showing the unfolding capacity to protein amyloid aggregates by physiologically relevant colloidal structures containing both dihydroxy and trihydroxy BS (Figure c).…”

“…3 More recently, we have elucidated that the indigestible intact protein (50 kDa) is the innate amyloid aggregates of 7S protein, and gastric digestion further triggers the novel formation of amyloid aggregates. 10 In this study, we isolated undigested protein aggregates from pepsin-trypsin digests of different soybean proteins (SPI, 11S, and 7S) by ultracentrifugation and analyzed in parallel by native-PAGE and SDS-PAGE. As shown in Figure 2a,b, the undigested fractions of SPI and 7S protein are composed of residue 7S protein amyloid aggregates and peptide fragments, while 11S and heated 7S protein (boiling for 30 min) only contain peptides fragments.…”

“…9 We have elucidated that pepsin digestion removed the charged extension region of α and α′ subunits in soybean 7S protein, leading to the formation of novel amyloid aggregates from the remaining core region of α and α′ subunits in soybean 7S protein. 10 This could trigger the new emergence of conformational epitopes present on the surface of indigestible 7S aggregates. Previously, Lin and Sampson 33 (2009) have indicated that more than 90% of IgE-binding epitopes of food allergens belong to conformational epitopes.…”

“…3,9 In a recent work, we have revealed that native soybean 7S protein containing innate amyloid aggregates and that gastric digestion triggered the novel formation of amyloid aggregates of soybean 7S protein and thus exhibited digestion resistance. 10 Meanwhile, we also illustrated that heat treatment promoted the digestion of soybean 7S protein via altering their ordered native structure, resulting in the destruction of a large number of epitopes in humans. 11 These results imply that the innate amyloid aggregates of soybean 7S protein could partially resist GI digestion, survive as large epitopes, and induce sensitization of the mucosal immune system after their absorption.…”

“…In the previous study, we found that native soybean 7S protein contained innate amyloid aggregates, and gastric digestion further triggered the novel formation of amyloid aggregates. 10 In this study, we focused on tracking the fate of these specific amyloid aggregates in the intestinal phase and their relation to immunogenicity. To achieve this, we propose a modified in vitro digestion approach by adding model bile into the intestinal digestion phase of the standardized INFOGEST static in vitro digestion model.…”