Exploring the mechanism of interaction between TBG and halogenated thiophenols: Insights from fluorescence analysis and molecular simulation.

Thyroxine-binding globulin (TBG) plays a vital role in regulating metabolism, growth, organ differentiation, and energy homeostasis, exerting significant effects in various key metabolic pathways. Halogenated thiophenols (HTPs) exhibit high toxicity and harmfulness to organisms, and numerous studies have demonstrated their thyroid-disrupting effects. To understand the mechanism of action of HTPs on TBG, a combination of competitive binding experiments, multiple fluorescence spectroscopy techniques, molecular docking, and molecular simulations was employed to investigate the binding mechanism and identify the binding site. The competition binding assay between HTPs and ANS confirmed the competition of HTPs with thyroid hormone T4 for the active site of TBG, resulting in changes in the TBG microenvironment upon the binding of HTPs to the active site. Key amino acid residues involved in the binding process of HTPs and TBG were further investigated through residue energy decomposition. The distribution of high-energy contributing residues was determined. Analysis of root-mean-square deviation (RMSD) demonstrated the stability of the HTPs-TBG complex. These findings confirm the toxic mechanism of HTPs in thyroid disruption, providing a fundamental reference for accurately assessing the ecological risk of pollutants and human health. Providing mechanistic insights into how HTPS causes thyroid diseases.

Investigations on the binding properties of hydroxylated polybrominated diphenyl ethers with lysozyme using the multispectral techniques and molecular modeling.

As a kind of phenolic chemical with endocrine disrupting potency, hydroxylated polybrominated diphenyl ethers (OH-PBDEs) cause a latent threat to human health from their residue in the environment. Their binding efficiency with lysozyme (LYSO) was studied by molecular simulation combined with fluorescence, UV-vis absorption and circular dichroism (CD), so as to assess their toxicity at the molecular level. Molecular docking data indicate that van der Waals force is the principal interaction force between OH-PBDEs and LYSO. The binding site for 5'-OH-BDE-25 in LYSO is ascertained as the active site, which interaction with the TRP63 and TRP108 residues of LYSO to take shape a strong face-to-face stacked rank (F-shaped). Both 4'-OH-BDE-99 and 3'-OH-BDE-154 display a certain degree of deviation from the active site. Nevertheless, their F-shaped interaction with TRP63 conduce to bind LYSO and stabilize the docking conformation. Combined with dynamics simulation and spectral analysis, the secondary structure of LYSO can be induced by the three kinds of OH-PBDEs. CD spectrum shows that the combination of LYSO and OH-PBDEs will make α- Helix content increased. The combination of OH-PBDEs and LYSO touch upon a static quenching mechanism as a result of steady state fluorescence. The energy decomposition analysis exhibited that LYSO-OH-PBDEs binding site was stable by van der Waals and hydrophobic interaction. As enzyme activity experiments demonstrate that OH-PBDEs can inhibit the activity of LYSO, which is helpful to clarify the molecular toxicity mechanism of OH-PBDEs.

Insight on the microscopic binding mechanism of bisphenol compounds (BPs) with transthyretin (TTR) based on multi-spectroscopic methods and computational simulations.

Thyroid hormones are involved in numerous physiological processes as regulators of metabolism, regulating organ growth, and mental state. Bisphenol compounds (BPs) are recognized as chemicals that interfere with endocrine balance. Because BPs have a similar structure to thyroxine, they can compete for binding to thyroid protein and disrupt the normal physiological activity of the thyroid system. In this study, three typical bisphenol compounds were selected to explore the interaction between BPs and TTR by computer simulations and multi-spectroscopic methods. The results revealed that BPs quenched the endogenous fluorescence of TTR via the combination of static quenching and non-radiative energy transfer, and the van der Waals forces and hydrogen bonding played a synergistic role in the binding process of BPs and TTR. Furthermore, the three-dimensional fluorescence spectroscopy, UV-vis spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, which were employed to determine the conformation of protein, revealed that binding of BPs with TTR could induce conformational changes in TTR. In addition, the binding sites and the residues surrounding the BPs within the TTR were determined through molecular docking and molecular dynamics simulation. Therefore, this work provides new insights into the interaction between BPs and TTR to evaluate the potential toxicity of BPs.

Exploring the toxic effects and mechanism of methoxylated polybrominated diphenyl ethers (MeO-PBDEs) on thyroxine-binding globulin (TBG): Synergy between spectroscopic and computations.

The interaction mechanism between thyroxine-binding globulin (TBG) and three methoxylated polybrominated diphenyl ethers (MeO-PBDEs) was analyzed by steady-state fluorescence, ultraviolet-visible (UV-visible) spectroscopy, circular dichroism (CD), molecular docking and molecular dynamics simulation methods. The results of the molecular docking technique revealed that 2'-MeO-BDE-3, 5-MeO-BDE-47, and 3-MeO-BDE-100 combined with TBG at the active site. The steady-state fluorescence spectra displayed that MeO-PBDEs quenched the endogenous fluorescence of TBG through static quenching mechanism, and complex formation between MeO-PBDEs and TBG was further indicated by UV-vis spectroscopy. The thermodynamic quantities showed that the binding process is spontaneous, and the major forces responsible for the binding are hydrogen bonding and hydrophobic interactions, which are consistent with the results of molecular docking to a certain extent. The results of CD confirmed that the secondary structure of TBG was changed after combining with MeO-PBDEs. The dynamic simulation results illustrated that the protein structure is more compact and changes in the secondary structure of TBG after binding to MeO-PBDEs. Additionally, we also utilized the molecular mechanics/Poisson-Boltzmann surface area (MM-PBSA) method to analyze the binding free energy of TBG and MeO-PBDEs. The results suggest that van der Waals force plays an essential role in the combination.