Characteristics of the interaction mechanisms of xylitol with β-lactoglobulin and β-casein: Amulti-spectral method and docking study

Elucidating thyroid hormone transport proteins disruption by nitrophenols through computational and spectroscopic analysis

Thyroxine (T4), as a type of thyroid hormone (TH), is a key hormone in regulating human metabolism, growth and development, central nervous system functions, and energy balance. It relies on TH transport proteins to reach cells and exert its biological actions. However, the binding of nitrophenol pollutants to TH transport proteins prevents the delivery of thyroid hormones to cells, thereby inhibiting the effects of the hormones. This study combines spectroscopic experiments and computational simulations to explore the mechanism of nitrophenols' interference with TH transport proteins. Detailed information on the quenching mechanism, binding parameters, interaction forces, binding models, and conformational changes of nitrophenols (PNP), chlorinated nitrophenols (CNP), and brominated nitrophenols (BNP) with TH transport proteins is obtained through spectroscopic experiments. Nitrophenols are found to form hydrogen bonds with residues Lys15, Arg378, and Arg381, respectively, thereby displacing T4 at the binding site in the TH transport proteins. With an increasing number of halogen atoms, the affinity of halogenated nitrophenols for TH transport proteins intensifies. Computational simulations are used to further understand the binding modes and binding sites, providing molecular-level insights into the binding of NPs in the cavity of TH transport proteins. Theoretical evidence from molecular docking and molecular dynamics (MD) simulations supports the experimental findings.

Comparative study of binding interactions between different fatty acids and β-lactoglobulin:Impact on conformation and physicochemical properties of the protein

A comparative study was conducted to investigate the binding mechanisms and interactions between four different lengths of saturated fatty acids (C12:0 to C18:0) and two types of C18 unsaturated fatty acids (C18:1 and C18:2) with β-lactoglobulin (β-Lg). The quenching mechanism for these six fatty acids - lauric acid (LUA), myristic acid (MA), palmitic acid (PAL), stearic acid (SA), oleic acid (OA), and linoleic acid (LA) - with β-Lg were found to be static, and the interactions were predominantly driven by hydrophobic forces. The binding affinity was increased with the increase of carbon chain. While, an increase in the number of CC double bonds resulted in a decreased in binding affinity. The binding of fatty acids interfered with the micro-environment around the tyrosine (Tyr) and tryptophan (Trp) residues in protein, subsequently altering the secondary structures of β-Lg. This study will help to improve our understanding of nutrient interactions in food.

The interaction of cinchonine and immunoglobulin G and the development of a nanocomplex with improved anti-breast cancer activity

In this study we evaluated the interaction of cinchonine (Cin) and immunoglobulin G (IgG). Then, Cin-IgG nanoparticles (NPs) were synthesized and characterized. Finally, the anticancer effects of free Cin and Cin-IgG NPs on MCF-7 breast cancer (BC) cells were evaluated. The results of spectroscopy measurements show that the IgG-Cin complex's quenching mechanism is static and the structure of IgG was partially changed following interaction with Cin. The prepared Cin-IgG NPs display a hydrodynamic size of 190 nm with a PDI of 0.269, a zeta potential of -38.05 mV, an EE% of 72.38 %, a LC% of 5.41 %, and a pH-sensitive drug release behavior. In the cellular assay, it was found that the calculated IC50 concentrations of Cin, IgG NPs, and Cin-IgG NPs are 66.4 ± 5.39, >100, and 29.2 ± ± 4.11 μM, respectively, in MCF-7 BC cells. Finally, Cin-IgG NPs induce a greater effect on the overexpression of the Bax/Bcl-2 ratio and downregulation of PI3K/p-AKT compared to the free drug. In conclusion, this study shows that Cin has the potential to bind IgG as a human plasma protein, and its complexation into a NP form with IgG can boost its anti-BC effects.

Impact of non-covalent interactions on the solvation of ovalbumin in an aqueous environment of different pHs: Thermodynamic and diffusion studies

The solvation behavior of protein is an important factor in protein-based food products. In the present study, the xylitol (XY) - ovalbumin (OVN) interaction in an aqueous solution of different pH conditions is analyzed in two methods. In one method, the thermodynamic parameters Gibbs free energy, free volume, and internal pressure are calculated by using ultrasonic velocity, density, and viscosity in addition the refractive index is also measured. The second method is a theoretical method in which using the Laplace transform technique the diffused amount of protein have been calculated for OVN with and without XY in different pH environment. The addition of XY with OVN makes the system with more free energy and free volume as the internal pressure decreases. This trend shows that preferential interaction occurs between solvent-solute molecules. The diffusivity of OVN is reduced after the addition of XY representing the strength of protein-protein interaction. The effect of pH changes is well reflected in both experimental and theoretical results. The results confirm that acidic pH extremity offers more solvation of OVN compared to alkaline pH extremity.

Inhibition effect of epicatechin gallate on acid phosphatases from rainbow trout (Oncorhynchus mykiss) liver by multispectral and molecular docking

Inhibition of acid phosphatase, which significantly contributes to inosine 5'-monophosphate (IMP) degradation, is crucial for preventing flavor deterioration of aquatic products during storage. In this study, the inhibitory effect of epicatechin gallate (ECG) on the activity of acid phosphatase isozymes (ACPI and ACPII) was analyzed using inhibition kinetics, fluorescence spectroscopy, isothermal titration calorimetry, and molecular simulation. ACPI and ACPII with molecular weights of 59.5 and 37.3 kDa, respectively, were purified from rainbow trout liver. ECG reversibly inhibited ACPI and ACPII activities via mixed-type inhibition, with half maximal inhibitory concentration (IC50) of 0.24 ± 0.01 mmol/L and 0.27 ± 0.03 mmol/L, respectively. Fluorescence spectra indicated that ECG statically quenched the intrinsic fluorescence of ACPI and ACPII. ECG could spontaneously bind to ACPI and ACPII through hydrogen bonding and van der Waals forces and exhibited a higher affinity for ACPI than for ACPII. In addition, molecular dynamic simulation revealed that ECG-ACPI and ECG-ACPII complexes were relatively stable during the entire simulation process. Our findings provide a theoretical basis for the use of ECG as an inhibitor of ACP to improve the flavor of aquatic products.

Small molecule linoleic acid inhibiting whey syneresis via interact with milk proteins in the fermentation of set yogurt fortified with c9,t11-conjugated linoleic acid

The study aimed to investigate the impact of fermentation conditions on c9,t11-conjugated linoleic acid (CLA) synthesis by Lactobacillus casei, as well as its effects on whey syneresis, water holding capacity (WHC), and texture characteristics of set yogurt. The amount of whey syneresis decreased about 30% with the adding of 0.1% linoleic acid (LA). The interaction between LA and casein (CS), β-lactoglobulin (β-Lg) and bovine serum albumin (BSA) was observed by UV-Vis absorption spectroscopy, 3D fluorescence spectroscopy and CD spectroscopy. It found that LA changed the microenvironment and polarity around amino acids, as well as the conformation of the three milk proteins. Scanning electron microscope (SEM) analysis revealed that the addition of LA resulted in a more uniform and compact microstructure of the set yogurt. It indicates that LA can promote the crosslink of milk proteins, which may be the reason for the reduction of whey syneresis in set yogurt.

Understanding molecular interaction between thermally modified β-lactoglobulin and curcumin by multi-spectroscopic techniques and molecular dynamics simulation

This study elucidated the binding of curcumin (CUR) onto preliminary thermally modified β-lactoglobulin (β-LG). β-LG at pH 8.1 was heated at 75 °C, 80 °C and 85 °C for 10 min to construct denatured proteins (β-LG75, β-LG80, β-LG85). Steady and time-resolved fluorescence studies uncovered that CUR quenched proteins in simultaneous static and dynamic mode. Pre-heating β-LG improved its binding with CUR and the strongest affinity occurred in β-LG80. Fluorescence resonance energy transfer (FRET) analysis indicated that binding distance between CUR and β-LG80 was the smallest and energy transfer was the most efficient. β-LG80 had the highest surface hydrophobicity. Fourier-transform infrared (FT-IR) spectroscopy and differential scanning calorimeter (DSC) confirmed that CUR transferred from crystal to amorphous state after association with protein and revealed the contribution of hydrogen bonds. Combination of β-LG80 with CUR retained the antioxidant capacity of each component. Molecular dynamics simulation demonstrated enhanced hydrophobic solvent accessible surface area of β-LG80 compared with native protein. Data obtained from this study may provide useful information for comprehensively understanding the ability of β-lactoglobulin to bind hydrophobic substances under different environmental conditions like high temperature and alkaline medium.

Characteristics of the interaction mechanisms of procyanidin B1 and procyanidin B2 with protein tyrosine phosphatase-1B: Analysis by kinetics, spectroscopy methods and molecular docking

Protein tyrosine phosphatase-1B (PTP1B) is a novel and indispensable drug target for the treatment of type 2 diabetes mellitus (T2DM). Procyanidins are flavonoids that exhibit a significant hypoglycemic function. However, the potential inhibitory effects of procyanidins on PTP1B are unclear. In this study, the interaction mechanisms of PTP1B with procyanidin B1 (PB1) and procyanidin B2 (PB2) were investigated through kinetics analysis, UV-visible spectroscopy, fluorescence spectroscopy, circular dichroism spectroscopy and molecular docking. The results showed that PB1 and PB2 could inhibit the activity of PTP1B in a mixed inhibition mode, which was one of the reversible inhibition types. Multi-spectral analysis showed that PB1/PB2 formed complexes with PTP1B, which effectively quenched the intrinsic fluorescence of PTP1B based on the static mechanism. The values of the binding constants were K_S(PTP1B-PB1) = 4.06 × 10² L·mol^-1 and K_S(PTP1B-PB2) = 2.53 × 10² L·mol^-1, indicating that the binding affinity of PTP1B to PB1 was higher than that for PB2. PB1 and PB2 both changed the secondary structure of the enzyme, thereby decreasing the PTP1B activity. Thermodynamic investigations revealed that the binding of procyanidin B1 and B2 to PTP1B was spontaneous in both cases, and highlighted the key role of hydrophobic interactions. Molecular docking analysis provided further information regarding the interactions between PB1 or PB2 and the amino acid residues of PTP1B. Moreover, PB1 and PB2 were found to down-regulate the expression level of PTP1B in insulin-resistant HepG2 cells. These findings are the first to elucidate the inhibitory effects of PB1 and PB2 on PTP1B, and highlight the role of procyanidins as dietary supplements in regulating T2DM.

Spectroscopic and docking studies of the interaction mechanisms of xylitol with α-casein and κ-casein

The molecular interactions of xylitol (XY) with α-casein (α-CN) and κ-casein (κ-CN) at pH 7.4 as a function of temperature (298, 308, and 318 K) were characterized by multispectral techniques and molecular docking. The fluorescence results showed that XY strongly quenched the intrinsic fluorescence of α- and κ-CN by static quenching, as well as the presence of a single binding site for XY on both proteins with a binding constant value of ∼10⁵ L/mol. The binding affinity of both proteins for XY decreased with increasing temperature, and Van der Waals forces, hydrogen bonding and protonation were the key forces in the interactions. The addition of XY altered the polarity of the microenvironment of proteins and changed their secondary structure from ordered to disordered. The molecular docking results showed that XY had different binding sites to α- and κ-CN, with several amino acids involved in the binding processes.

Spectrofluorimetric analysis of the binding of a target molecule to serum albumin: tricky aspects and tips

Protein binding heavily modulates drug activity. Therefore, the binding features need to be elucidated when chemistry researchers study new molecules (metal complexes) to be used as drugs. This paper concerns the experimental and data treatment aspects of the mechanistic analysis of the binding to a fluorescent protein (the golden standard serum albumin) by using direct fluorescence titrations. Fluorescence data are not rarely only qualitatively used, neglecting further treatments which could offer a precious detailed picture of the behavior of the drug. We aim to spread a mechanistic approach, discussing the critical aspects for correctly designing the experiments and treating the data. The researcher may confirm adduct formation and evaluate binding constants (Stern-Volmer KSV or other types of K). Also, we discuss here, with the help of literature examples, the correct use of temperature dependence of K to extract thermodynamic parameters, comment on enthalpy-entropy compensation, together with the use of synchronous spectra and exchange experiments to gain information on the binding type and site. We think that this tutorial/critical synopsis can be of help for the increasing community dealing with these experiments, which are valuable but often much more tricky than it might appear at first sight.