Structural modifications and augmented affinity for bile salts in enzymatically denatured egg white

Abstract

Protein binding to bile salts (BSs) reduces cholesterol levels, but the exact mechanism is unclear. In this study, we performed simulated gastrointestinal digestion of egg white protein hydrolysate (EWPHs) and included an unenzyme digestion group (CK) to investigate the changes in BSs binding capacity before and after digestion, as well as the relationship between egg white protein (EWP) structure and BSs binding capacity. In addition, peptidomics and molecular docking were used to clarify EWP's binding mechanism. We found that the BSs binding ability of EWPHs was slightly decreased after digestion, but significantly higher than that of the CK group and the digested CK group (D-CK). Particle size analysis and electrophoresis demonstrated that smaller particles and lower molecular weights exhibited enhanced binding capacity to BSs. Fourier Transform infrared spectroscopy (FTIR) results revealed that a disordered structure favored BS binding ability enhancement. Peptides FVLPM and GGGVW displayed hypocholesterolemic efficacy.

Keywords: Bile salts binding ability; Egg white protein; In vitro simulation of gastrointestinal digestion; Structure-activity relationship.

Fig. 1

(A) Bile salt binding rate of EWP in simulated gastrointestinal digestion before and after enzymolysis. Means with different lowercase (apply to comparisons among different bile salt at a distinct treatment) superscripts differ significantly (p < 0.05), (B) Total sulfhydryl content of CK, EWPHs, D-CK and D-EWPHs, (C) Surface hydrophobicity of CK, EWPHs, D-CK and D-EWPHs, (D) Particle sizes of CK, EWPHs, D-CK and D-EWPHs, and (E) SDS-PAGE (E1) and Tricine-SDS-PAGE (E2) of CK, EWPHs, D-CK and D-EWPHs.

Fig. 2

(A) UV spectra of CK, EWPHs, D-CK and D-EWPHs, (B) Intrinsic fluorescence spectra of CK, EWPHs, D-CK and D-EWPHs, (C) FTIR spectra (C1) and secondary structure-occupied stacking maps (C2) of CK, EWPHs, D-CK and D-EWPHs, and (D) SEM images of EWP under different treatments (D1) CK group (D2) EWPHs group (D3) D-CK group (D4) D-EWPHs group.

Fig. 3

Effect of different treatments on rheological properties of EWP: (A) Apparent viscosity, (B) Shear stress, (C) Storage modulus, and (D) Loss modulus.

Fig. 4

(A) Analysis of EWP heat map before and after enzymatic hydrolysis and digestion. Where EW: EWPHs; DCK: D-CK; DE: D-EWPHs; where the darker red color represents the higher relative abundance of peptides and the darker blue color represents the lower relative abundance of peptides, and (B) Heat map analysis of EWP cholesterol-lowering peptide before and after enzymolysis and digestion. Where EW: EWPHs; DCK: D-CK; DE: D-EWPHs; where the darker red color represents the higher relative abundance of peptides and the darker blue color represents the lower relative abundance of peptides. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

(A1-A3) Prediction of the interaction between ovalbumin and bile salt molecules. Where A1 is the interaction force between ovalbumin and sodium cholate molecules; A2 is the interaction force between ovalbumin and sodium taurocholate molecules; A3 is the interaction force between ovalbumin and sodium deoxycholate molecules; where blue bar structures represent amino acid residues in ovalbumin that interact with bile salt molecules, yellow bar structures are bile salt molecules, gray dashed lines connect hydrophobic interactions, and blue solid lines connect hydrogen bonding interactions. (B1-B2) Three-dimensional molecular docking image of ovalbumin and bile salt. Where B1 is the molecular docking image of ovalbumin with sodium cholate; B2 is the molecular docking image of ovalbumin with sodium taurocholate; B3 is the molecular docking image of ovalbumin with sodium deoxycholate; where the green bar structure represents the amino acid residues in ovalbumin that interact with the bile salt molecule, and the blue bar structure is the bile salt molecule. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)