Wansong Zong

Evaluation on the toxicity of nanoAg to bovine serum albumin

Measuring protein damage by nanomaterials may give insight into the mechanisms of toxicity of nanomaterials. The toxic effects of nanoAg on bovine serum albumin (BSA) were thoroughly studied using fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, resonance light scattering spectroscopy (RLS), circular dichroism spectroscopy (CD) and transmission electron microscopy (TEM). NanoAg had obvious toxic effects on BSA: nanoAg could increase the amount of helix and decrease the beta sheet structure, leading to a loosening of the protein skeleton. In the loose structure, internal hydrophobic amino acids are exposed and the characteristic fluorescence of BSA is obviously quenched. When the ratio of nanoAg and BSA increased to 1: 96 (wt/wt), the impact of nanoAg on the spectral properties leveled off. The RLS spectrum, TEM, CD spectra and electrophoresis results showed that BSA had destroyed the double-layer structure of nanoAg and covered its surface, generating a BSA-nanoAg complex held together by van der Waals and electrostatic forces. This paper provides a new perspective and method for determining the toxic effects of nanoAg on biological macromolecules.

A New Strategy to Identify and Eliminate the Inner Filter Effects by Outer Filter Technique

To identify and eliminate the inner filter effects (IFEs), prepositive and side cells containing absorbents are fixed beside the fluorescer contained cell. In this way, excitation and emission lights can be quenched by primary and secondary outer filter effects respectively, depending on absorbent concentration and cell length. Herein the quenching of emission fluorescence caused by IFEs can be equally reduced by outer filter effects (OFEs) and the interference of IFEs was eliminated. This approach was experimentally used for identifying the interaction mode and mechanism between BSA and nanoAg. Results showed that the quenching of BSA fluorescence and synchronous fluorescence mainly attributes to IFEs, instead of static/dynamic fluorescent quenching. In view of the above, the elimination of the interference of IFEs by the design of OFEs plays an important part in the precise application of fluorescence detector.

Bisphenol S Interacts with Catalase and Induces Oxidative Stress in Mouse Liver and Renal Cells

Bisphenol S (BPS) is present in multitudinous consumer products and detected in both food and water. It also has been a main substitute for bisphenol A (BPA) in the food-packaging industry. Yet, the toxicity of BPS is not fully understood. The present study of the toxicity of BPS was divided into two parts. First, oxidative stress, cell viability, apoptosis level, and catalase (CAT) activity in mouse hepatocytes and renal cells were investigated after BPS exposure. After 12 h of incubation with BPS, all of these parameters of hepatocytes and renal cells changed by >15% as the concentration of BPS ranged from 0.1 to 1 mM. Second, the direct interaction between BPS and CAT on the molecule level was investigated by multiple spectral methods and molecular docking investigations. BPS changed the structure and the activity of CAT through binding to the Gly 117 residue on the substrate channel of the enzyme. The main binding forces were hydrogen bond and hydrophobic force.

Micro-environmental influences on the fluorescence of tryptophan.

The fluorescence characteristics of protein molecules are mainly due to their tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe) residues, among which tryptophan is the most important. Studying the influence of the micro-environment on tryptophan fluorescence can give us direct and convincing evidence for changes of protein structure and function. In this paper, fluorescence spectroscopy was used to evaluate the changes of tryptophan fluorescence under a variety of micro-environmental conditions (temperature, pH, polarity, presence of surfactants and oxidants) and the mechanisms responsible. This study not only presents more direct evidence to explain how and why the protein fluorescence spectra change, but also provides a new method for analyzing the effect of environmental changes on protein function.

Probing the binding interaction between cadmium(II) chloride and lysozyme

The direct binding of cadmium with lysozyme might cause the structural and functional changes of lysozyme. To better understand the potential toxicity and toxic mechanisms of cadmium, it is of vital importance to characterize the interaction of cadmium with lysozyme. This article investigated the interaction of cadmium chloride (CdCl2) with lysozyme using biophysical methods including the spectroscopic technique, isothermal titration calorimetry (ITC), molecular docking and dynamics simulation studies, and enzyme activity measurements. ITC measurements indicated that the interaction is mainly driven by hydrophobic forces with approximately 3 thermodynamic identical binding sites at 310.15 K. Multi-spectroscopic measurements showed that CdCl2 statically quenched the intrinsic fluorescence of lysozyme, formed complexes with lysozyme and altered its secondary structure. Also, the topology of lysozyme in the presence of CdCl2 was altered. Although complexes were formed, we observed no change of lysozyme activity at low CdCl2 concentration because CdCl2 does not preferentially bind to the active site of lysozyme.

Cyclic voltammetry: A new strategy for the evaluation of oxidative damage to bovine insulin

Research on protein oxidative damage may give insight into the nature of protein functions and pathological conditions. In this work, the oxidative damage of bovine insulin on Au electrode was investigated by cyclic voltammetry (CV). The experimental results show that there are two anodic peaks for the oxidative damage of bovine insulin, which arise from the oxidation of the exposed disulfide bond SSCYS7A,CYS7B, forming sulfenic acid RSOH (1.20 V, vs. SCE), sulfinic acid RSO2H and sulfonic acid RSO3H (1.35 V, vs. SCE). These in vitro findings not only demonstrate the applicability of CV in simulating/evaluating the oxidative damage of nonredox proteins but also find two promising candidates (two anodic peaks) for measuring insulin.

Spectroscopic investigation on the interaction of Cr(VI) with bovine serum albumin

The interaction of potassium dichromate (Cr(VI)) with bovine serum albumin (BSA) was investigated by fluorescence, synchronous fluorescence, resonance light scattering (RLS), ultraviolet–visible absorption, and circular dichroism (CD) spectroscopies under simulated physiological conditions. The experimental results showed that Cr(VI) could quench the intrinsic fluorescence of BSA following a static quenching process, which indicates the formation of a Cr(VI)–BSA complex. The binding constant (KA) and binding site (n) were measured at different temperatures. The spectroscopic results also revealed that the binding of Cr(VI) to BSA can lead to the loosening of the protein conformation and can change the microenvironment and skeleton of BSA.

A Unique Approach to the Mobile Proton Model: Influence of Charge Distribution on Peptide Fragmentation

The cleavage processes of protonated peptides in mass spectrometry, described in the mobile proton model, are charge-directed and depend on the charge distribution around the cleavage sites. Previous studies experimentally verified the mobile proton model by changing peptide sequences. In this study, oxidation was applied to change the charge distribution of peptides, but the sequence was retained. Tandem mass spectrometry (MS/MS) and quantum chemical calculations at the B3LYP/6-31G(d) level were used to test the validity of the mobile proton model. The results showed prominent differences of peptide fragmentation efficiency caused by the charge distribution produced by various oxidation levels. Fragmentation efficiency curves coupled with the relative intensities of the fragments indicated that the cleavage of the peptide Ala-Arg-Arg-Ala (ARRA) became more and more difficult as O atoms were added. The relative charge ratios between C and N atoms in the amide bonds decreased with the increase of oxidation extent, suggesting that oxidation resulted in protons moving away from the amide bonds. The combined methods proposed here provide a unique approach to substantiate and refine the mobile proton model for peptide fragmentation.

The oxidative products of methionine as site and content biomarkers for peptide oxidation

Biomarkers for peptide/protein oxidation under oxidative stress (OS) hold both incredible application potential as well as significant challenges. In this article, liquid chromatography and mass spectrometry were applied to establish a new method for evaluating the oxidation site and degree of peptide oxidized, with its oxidative product serving as biomarker. In the three model peptides, peptide FMRF (containing a methionine) was prone to undergo oxygen addition under UV/H2O2 oxidization, forming a sulfoxide (FM(O)RF) with a stable chromatographic peak separate from the model peptides. The oxidation content of FMRF, expressed as SFM(O)RF/(SFM(O)RF + SFMRF), is positively correlated with oxidation time. Based on sequence analysis of FM(O)RF, the oxidation mechanism (site and extent) of FMRF under UV/H2O2 oxidization was explicitly clarified. By comparing the specific injury to each model peptide, we found that the oxidative products of Met‐containing peptides are good biomarkers for OS. This research not only expands the range of biomarkers for OS, but also provides an efficient and accurate method for evaluating oxidation damage to peptides and even proteins. Copyright

A new biomarker of protein oxidation degree and site using angiotensin as the target by MS

Hydroxyl radicals generated from Fenton reaction were used to damage the angiotensin. The oxidative damage degree and sites of peptides were measured by HPLC-MS and MS/MS. Experimental results proved that the oxidative damage degree increased with longer reaction time. The results also showed that the side chains of phenylalanine and tyrosine in angiotension can be attacked by hydroxyl radicals to form the oxidative products. A new strategy was established to monitor the oxidative degree and sites of peptides and laid the foundation for protein oxidation. This method can be used to investigate the mechanism of protein oxidative damage caused by oxidative stress which is induced by environmental pollutants and physiological activities. There will also be a wide application in the research of pathogenesis of some disease related to oxidative stress.