Binding of brilliant red compound to lysozyme: insights into the enzyme toxicity of water-soluble aromatic chemicals

Potential toxicity of sulfanilamide antibiotic: binding of sulfamethazine to human serum albumin

Antibiotics are widely used in daily life but their abuse has posed a potential threat to human health. The interaction between human serum albumin (HSA) and sulfamethazine (SMZ) was investigated by capillary electrophoresis, fluorescence spectrometry, and circular dichroism. The binding constant and site were determined to be 1.09×10(4) M(-1) and 1.14 at 309.5 K. The thermodynamic determination indicated that the interaction was driven by enthalpy change, where the electrostatic interaction and hydrogen bond were the dominant binding force. The binding distance between SMZ and tryptophan residue of HSA was obtained to be 3.07 nm according to Fǒrster non-radioactive energy transfer theory. The site marker competition revealed that SMZ bound into subdomain IIA of HSA. The binding of SMZ induced the unfolding of the polypeptides of HSA and transferred the secondary conformation of HSA. The equilibrium dialysis showed that only 0.13 mM SMZ decreased vitamin B(2) by 38% transported on the HSA. This work provides a new quantitative evaluation method for antibiotics to cause the protein damage.

Interactions of hydroxyapatite with proteins and its toxicological effect to zebrafish embryos development

The increased application of nanomaterials has raised the level of public concern regarding possible toxicities caused by exposure to nanostructures. The interactions of nanosized hydroxyapatite (HA) with cytochrome c and hemoglobin were investigated by zeta-potential, UV-vis, fluorescence and circular dichroism. The experimental results indicated that the interactions were formed via charge attraction and hydrogen bond and obeyed Langmuir adsorption isotherm. The two functional proteins bridged between HA particles to aggregate into the coralloid form, where change of the secondary structure of proteins occurred. From effects of nanosized HA, SiO(2) and TiO(2) particles on the zebrafish embryos development, they were adsorbed on the membrane surface confirmed by the electronic scanning microscopy. Nano-HA aggregated into the biggest particles around the membrane protein and then caused a little toxicity to development of zebrafish embryos. The SiO(2) particles were distributed throughout the outer surface and caused jam of membrane passage, delay of the hatching time and axial malformation. Maybe owing to the oxygen free radical activity, TiO(2) caused some serious deformity characters in the cardiovascular system.

Transmembrane transports of acrylamide and bisphenol A and effects on development of zebrafish (Danio rerio)

Acrylamide (AA) and bisphenol A (BPA) are two kinds of pollutants with different structures and polarities. AA found in fried and toasted starchy foods can cause developmental and reproductive toxicity and BPA has neuro-, immuno- and developmental toxicities. Their transports in zebrafish (Danio rerio) embryos were determined and their toxicity characteristics observed. Approximately 70% of AA was concentrated on the outer membrane surface probably via hydrogen bonds and van der Waals forces, but only 0.3% of AA entered the cytoplasm. In contrast, over 10% of the BPA adsorbed to the cells entered the cytoplasm via the membrane by lipid-water partition. The hydrophilic AA and hydrophobic BPA used different cell transport pathways; AA accumulated on the outer membrane surface whereas BPA readily reached the cytoplasm. AA caused acute and indirect toxicity in developing cells, including serious malnutrition and axial malformation. BPA caused chemical damage to developing cells by causing pericardial edema. The antagonistic effect of the AA/BPA mixture's combinational toxicity to embryos was found and explained by the accumulation of AA on the out surface of membrane inhibiting the transfer of BPA to the cytoplasm.

Binding of bisphenol A and acrylamide to BSA and DNA: insights into the comparative interactions of harmful chemicals with functional biomacromolecules

The interactions between bisphenol A (BPA)/acrylamide (AA) and bovine serum albumin (BSA)/deoxyribonucleic acid (DNA) was investigated by the equilibrium dialysis, fluorophotometry, isothermal titration calorimetry (ITC) and circular dichroism (CD). The bindings of BPA and AA to BSA and DNA responded to the partition law and Langmuir isothermal model, respectively. The saturation mole number of AA was calculated to be 24 per mol BSA and 0.26 per mol DNA-P. All the reactions were spontaneous driven by entropy change. BPA stacked into the aromatic hydrocarbon groups of BSA and between adjacent basepairs of DNA via the hydrophobic effect. The interactions of AA with BSA and DNA induced the formation of hydrogen bond and caused changes of their secondary structures. At normal physiological condition, 0.100 mmol/l BPA reduced the binding of vitamin B(2) to BSA by more than 70%, and 2.8 mmol/l AA by almost one half. This work provides an insight into non-covalent intermolecular interaction between organic contaminant and biomolecule, helping to elucidate the toxic mechanism of harmful chemicals.

Potential enzyme toxicity of oxytetracycline to catalase

Oxytetracycline (OTC) is a kind of widely used veterinary drugs. The residue of OTC in the environment is potentially harmful. In the present work, the non-covalent toxic interaction of OTC with catalase was investigated by the fluorescence spectroscopy, UV-vis absorption and circular dichroism (CD) spectroscopy at physiological pH 7.4. OTC can interact with catalase to form a complex mainly by van der Waals' interactions and hydrogen bonds with one binding site. The association constants K were determined to be K(293K)=7.09×10(4)Lmol(-1) and K(311K)=3.31×10(4)Lmol(-1). The thermodynamic parameters (ΔH°, ΔG° and ΔS°) of the interaction were calculated. Based on the Förster theory of non-radiative energy transfer, the distance between bound OTC and the tryptophan residues of catalase was determined to be 6.48nm. The binding of OTC can result in change of the micro-environment of the tryptophan residues and the secondary structure of catalase. The activity of catalase was also inhibited for the bound OTC. This work establishes a new strategy to probe the enzyme toxicity of veterinary drug residues and is helpful for clarifying the molecular toxic mechanism of OTC in vivo. The established strategy can be used to investigate the potential enzyme toxicity of other small organic pollutants and drugs.

Interaction of nano-TiO2 with lysozyme: insights into the enzyme toxicity of nanosized particles

BACKGROUND, AIM, AND SCOPE

Nanomaterials have been used increasingly in industrial production and daily life, but their human exposure may cause health risks. The interactions of nanomaterial with functional biomolecules are often applied as a precondition for its cytotoxicity and organ toxicity where various proteins have been investigated in the past years. In the present study, nano-TiO(2) was selected as the representative of nanomaterials and lysozyme as a representative for enzymes. By investigating their interaction by various instrumentations, the objective is to identify the action sites and types, estimate the effect on the enzyme structure and activity, and reveal the toxicity mechanism of nanomaterial.

MATERIALS AND METHODS

Laboratory-scale experiments were carried out to investigate the interactions of nano-TiO(2) with lysozyme. The interaction of nano-TiO(2) particles with lysozyme has been studied in the analogous physiological media in detail by UV spectrometry, fluorophotometry, circular dichroism (CD), scanning electron microscope, zeta-potential, and laser particle size.

RESULTS

The interaction accorded with the Langmuir isothermal adsorption and the saturation number of lysozyme is determined to be 580 per nano-TiO(2) particle (60 nm of size) with 4.7 x 10(6) M(-1) of the stability constant in the physiological media. The acidity and ion strength of the media obviously affected the binding of lysozyme. The warping and deformation of the lysozyme bridging were demonstrated by the conversion of its spatial structure from alpha-helix into a beta-sheet, measured by CD. In the presence of nano-TiO(2), the bacteriolysis activity of lysozyme was subjected to an obvious inhibition.

DISCUSSION

The two-step binding model of lysozyme was proposed, in which lysozyme was adsorbed on nano-TiO(2) particle surface by electrostatic interaction and then the hydrogen bond (N-H...O and O-H...O) formed between nano-TiO(2) particle and polar side groups of lysozyme. The adsorption of lysozyme obeyed the Langmuir isothermal model. The binding of lysozyme is dependent on the acidity and ion strength of the media. The bigger TiO(2) aggregate was formed in the presence of lysozyme where lysozyme may bridge between nano-TiO(2) particles. The coexistence of nano-TiO(2) particles resulted in the transition of lysozyme conformation from an alpha-helix into a beta-sheet and a substantial inactivation of lysozyme. The beta-sheet can induce the formation of amyloid fibrils, a process which plays a major role in pathology.

CONCLUSIONS

Lysozyme was adsorbed on the nano-TiO(2) particle surface via electrostatic attraction and hydrogen bonds, and they also bridged among global nano-TiO(2) particles to form the colloidal particles. As a reasonable deduction of this study, nano-TiO(2) might have some toxic impacts on biomolecules. Our data suggest that careful attention be paid to the interaction of protein and nanomaterials. This could contribute to nanomaterial toxicity assessment.

RECOMMENDATIONS AND PERSPECTIVES

Our results strongly suggest that nano-TiO(2) has an obvious impact on biomolecules. Our data suggest that more attention should be paid to the potential toxicity of nano-TiO(2) on biomolecules. Further research into the toxicity of nanosized particles needs to be carried out prior to their cell toxicity and tissue toxicity. These investigations might serve as the basis for determining the toxicity and application of nanomaterials.