Abstract
Given that bisphenols have an endocrine-disrupting effect on human bodies, thoroughly exposing their potential effects at the molecular level is important. Saturation transfer difference (STD) NMR-based binding studies were performed to investigate the binding potential of two bisphenol representatives, namely, bisphenol B (BPB) and bisphenol E (BPE), toward human serum albumin (HSA). The relative STD (%) suggested that BPB and BPE show similar binding modes and orientations, in which the phenolic rings were spatially close to HSA binding site. ITC analysis results showed that BPB and BPE were bound to HSA with moderately strong binding affinity through electrostatic interactions and hydrogen bonds. The order of binding affinity of HSA for two test bisphenols is as follows: BPE > BPB. The results of fluorescence competitive experiments using 5-dimethylaminonaphthalene-1-sulfonamide and dansylsarcosine as competitors, combined with molecular docking indicated that both bisphenols are prone to attach to the binding site II in HSA. Spectroscopic results (FT-IR, CD, synchronous and 3D fluorescence spectra) showed that BPB/BPE induces different degrees of microenvironmental and conformational changes to HSA.
Highlights
Endocrine disruptors (EDs) are exogenous substances that interfere with hormone biosynthesis and metabolism or cause deviation from normal homeostatic control or reproduction[1, 2]
Clear Saturation transfer difference (STD) signals are observed in all the bisphenol B (BPB) and bisphenol E (BPE) protons, indicating that protein saturation distributed onto the BPB and BPE, which bind to Human serum albumin (HSA) under our experimental conditions
In comparing with the spectrum of HSA, the spectra of HSA-BPs systems exhibited a slight wavelength red shift and an obvious wavelength blue shift in the amides I and II bands. These results indicated that BPB and BPE interacted with both the C = O, C-N, and N-H groups in the polypeptides of HSA that results in conformational changes in the secondary structure of HSA37, 38
Summary
Endocrine disruptors (EDs) are exogenous substances that interfere with hormone biosynthesis and metabolism or cause deviation from normal homeostatic control or reproduction[1, 2]. Bisphenol B (BPB, 2,2-bis(4-hydroxyphenyl)butane)) and bisphenol E (BPE, 4,4′-ethylidenebisphenol) are bisphenol-type compounds, which are derivatives of BPA. The present work is a comprehensive in vitro study on the interaction of BPs with HSA using 1H saturation transfer difference nuclear magnetic resonance (STD-NMR), isothermal titration calorimetry (ITC), Fourier transform infrared (FT-IR), circular dichroism (CD), synchronous and 3D fluorescence spectroscopy, and molecular docking simulation. These techniques are complementary, and their findings were consistent with one another. The effects of BPs on local HSA conformation and the microenvironment of tryptophan (Trp) residue were examined through FT-IR, CD, synchronous and 3D fluorescence spectroscopy
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