Stabilization of apo α-lactalbumin by binding of epigallocatechin-3-gallate: Experimental and molecular dynamics study

Elucidating the interaction mechanism of rutin with β-casein and β-lactoglobulin: A comprehensive analysis using multi-spectroscopy, molecular docking, and molecular dynamic simulations

Polyphenol-protein interactions are crucial for food processing, nutrition, and functional properties. This study investigates the interaction between rutin and β-casein (β-CAS) or β-lactoglobulin (β-LG) using multispectral analysis, molecular docking, and molecular dynamics (MD) simulations. Fluorescence spectroscopy reveals that rutin binds spontaneously (ΔG < 0) to β-CAS and β-LG, forming complexes with binding constants (Ka) at 298 K of 42.500 × 103 and 2.101 × 103 L·mol-1, respectively, and at 308 K of 5.814 × 103 and 4.350 × 103 L·mol-1. Multispectral analysis and microscopy reveal complex formation and changes in the proteins' secondary, crystalline, and microstructures. Molecular docking and MD simulations verify complex stability, showing heightened binding affinity between rutin and β-CAS. These results validate hydrophobic interactions and hydrogen bonding as the main forces between rutin and the two proteins. These findings offer insights for using milk proteins as rutin carriers and support potential food industry application.

Tailoring ternary complexes of lactoferrin, EGCG, and α-lactalbumin by assembly sequence strategies: Structural characterization, assembly mechanism, and emulsification elucidation

Three distinct ternary complexes (TC-M1, TC-M2, and TC-M3) based on lactoferrin (LF), (-)-epigallocatechin-3-gallate (EGCG), and α-lactalbumin (ALA) were prepared by varying the assembly sequence and EGCG concentrations (ranging from 0 to 2.0 mM). Structural characterization was performed using various spectroscopic techniques, while the assembly mechanisms were investigated through ITC and molecular docking. These ternary complexes were further evaluated as stabilizers in Pickering emulsions. Nephelometry and DLS analysis showed that TC-M1 exhibited the highest turbidity and largest particle size, followed by TC-M2 and TC-M3. FT-IR and fluorescence spectroscopy revealed strong binding between EGCG and both ALA and LF, enhancing the hydrophilicity and extending structure of proteins. ITC and molecular docking studies indicated spontaneous interactions primarily driven by hydrogen bonding and hydrophobic forces, with LF (Ka1 = 1.9 × 105 M-1) and ALA (Ka1 = 3.6 × 104 M-1) binding approximately 3.3 and 2.9 EGCG molecules, respectively. Pickering emulsions formed by these complexes demonstrated superior emulsification properties, with TC-M1 showing the smallest CI (10.09 % ± 0.19 %), particle size (1 to 2 μm), and higher MVI (1.2) and EI (2.5) at 2.0 mM EGCG, outperforming TC-M2 and TC-M3 in stability. Overall, the assembly sequence of LF, ALA, and EGCG, along with EGCG concentration, lays the foundation for designing protein-polyphenol-protein ternary complexes, offering enhanced stability and functionality for diverse EGCG delivery applications.

Heat treatment effect on whey protein-epigallocatechin gallate interaction: A fluorescence spectroscopic analysis

This study aimed to examine the interaction mechanism of polyphenol protein in a heat-treated aqueous solution system using epigallocatechin gallate (EGCG) and whey protein (WP) as raw materials. Further, we hypothesized the binding characteristics of these two compounds. The results were as follows: The quenching mechanism between WP and EGCG was characterized as static quenching. As the temperature increased, the binding constant and the binding force between EGCG and WP both increased. The number of binding sites (denoted as n) between WP and EGCG was approximately 1. Hence, WP provided a single site to bind to EGCG to form a complex. The main binding modes between WP and EGCG were hydrophobic and electrostatic interactions, and they were spontaneously combined into complexes (ΔG < 0). This study provided a basis for the interaction between WP and EGCG under different heating conditions and their combination mode.

Investigation of binding interaction between bovine α-lactalbumin and procyanidin B2 by spectroscopic methods and molecular docking

The interactions between bovine α-lactalbumin and procyanidin B2 were fully investigated by spectroscopic methods and molecular docking. This study hypothesized that ALA could spontaneously interact with procyanidin B2 to form protein-based complex delivery carrier. Far UV CD and FTIR data demonstrated ALA's secondary structures were altered and intrinsic fluorescence quenching suggested ALA conformation was changed with procyanidin B2. Calorimetric technique illustrated ALA-procyanidin B2 complexation was a spontaneous and exothermic process with the number of binding site (n, 3.53) and the binding constant (K_b, 2.16 × 10⁴ M^-1). A stable nano-delivery system with ALA can be formed for encapsulating, stabilizing and delivering procyanidin B2. Molecular docking study further elucidated that hydrogen bonds dominated procyanidin B2 binding to ALA in a hydrophobic pocket. This study shows great potential in using ALA as protein-based nanocarriers for oral delivery of hydrophilic nutraceuticals, because procyanidin B2-loaded ALA complex delivery systems can be spontaneously formed.

Impacts of Ca2+ cation and temperature on bovine α-lactalbumin secondary structures and foamability - Insights from computational molecular dynamics

We used computational molecular dynamics (MD) to assess molecular conformations of apo- and holo-forms (respectively without and with Ca²⁺) of bovine α-lactalbumin (α-La) at different temperatures, and to correlate them with the protein's foaming properties. At 4 °C and 25 °C no major protein conformation changes occurred. At 75 °C, lots of changes were evidenced: the Ca²⁺ depletion triggered the complete loss of h2b, h3c helices and S1, S2 and S3 β-sheets, and partial losses of H1, H2 and H3 α-helices. The absence of Ca²⁺ in apo-α-La and its leaving from holo-α-La triggered electrostatic repulsion among Asp82, Asp84 and Asp87, leading to the formation of a hydrophobic cluster involving Phe9, Phe31, Ile1, Va42, Ile55, Phe80 and Leu81. These conformational changes were related to an interfacial tension decrease and to a foaming capacity increase, for both apo-α-La and holo-α-La. This study exemplifies how powerful MD is as a tool to provide a better understanding of the molecular origins of food proteins' techno-functionalities.

Gallic Acid-Aided Cross-Linking of Myofibrillar Protein Fabricated Soluble Aggregates for Enhanced Thermal Stability and a Tunable Colloidal State

Low colloidal stability of myofibrillar protein (MP) during heating is a technofunctional constraint encountered in its beverage application. Gallic acid (GA), a natural polyphenol, was applied to fabricate MP soluble aggregates for an enhanced thermal stability. Upon pH shifting, GA was grafted into MP with the cysteine and tryptophan residues being the binding sites. As a result, the antioxidant activity of MP was enhanced. Additionally, GA modification decreased the α-helix structure of MP and converted MP into cross-linked aggregates. At low dosages (10 and 25 μmol/g GA), disulfide-dominant covalent bonds were formed to generate myosin and actin aggregates, while MP aggregates were mostly bridged through GA-thiols or GA-tryptophan adducts when the dosages exceeded 50 μmol/g. Such aggregates prevented MP from thermal gelation, leading to a stable and tunable colloidal state. This work can foster technological advances in the tailor manufacture of muscle protein-based beverages for special dietary uses.

A look back at the molten globule state of proteins: thermodynamic aspects

Interest in protein folding intermediates lies in their significance to protein folding pathways. The molten globule (MG) state is one such intermediate lying on the kinetic (and sometimes thermodynamic) pathway between native and unfolded states. Development of our qualitative and quantitative understanding of the MG state can provide deeper insight into the folding pathways and hence potentially facilitate solution of the protein folding problem. An extensive look at literature suggests that most studies into protein MG states have been largely qualitative. Attempts to obtain quantitative insights into MG states have involved application of high-sensitivity calorimetry (differential scanning calorimetry and isothermal titration calorimetry). This review addresses the progress made in this direction by discussing the knowledge gained to date, along with the future promise of calorimetry, in providing quantitative information on the structural features of MG states. Particular attention is paid to the question of whether such states share common structural features or not. The difference in the nature of the transition from the MG state to the unfolded state, in terms of cooperativity, has also been addressed and discussed.