Potential enzyme toxicity of perfluorooctanoic acid

Nanoplastics composite norfloxacin induced changes in conformation and function of lysozyme and differential effects of co-exposure contamination

The concurrent environmental contamination by nanoplastics (NPs) and norfloxacin (NOR) is a burgeoning concern, with significant accumulations in various ecosystems and potential ingress into the human body via the food chain, posing threats to both public health and ecological balance. Despite the gravity of the situation, studies on the co-exposure contamination effects of these substances are limited. Moreover, the response mechanisms of key functional proteins to these pollutants are yet to be fully elucidated. In this work, we conducted a comprehensive assessment of the interaction mechanisms of NPs and NOR with lysozyme under both single and co-exposure condition, utilizing dynamic light scattering, ζ-potential measurements, multi-spectroscopy methods, enzyme activity assays and molecular docking, to obtain a relationship between the compound effects of NPs and NOR. Our results indicate that NPs adsorb NOR on their surface, forming more stable aggregates. These aggregates influence the conformation, secondary structure (α-Helix ratio decreased by 3.1 %) and amino acid residue microenvironment of lysozyme. And changes in structure affect the activity of lysozyme (reduced by 39.9 %) with the influence of composited pollutants exerting stronger changes. Molecular simulation indicated the key residues Asp 52 for protein function located near the docking site, suggesting pollutants preferentially binds to the active center of lysozyme. Through this study, we have found the effect of increased toxicity on lysozyme under the compounded conditions of NPs and NOR, confirming that the increased molecular toxicity of NPs and NOR is predominantly realized through the increase in particle size and stability of the aggregates under weak interactions, as well as induction of protein structural looseness. This study proposes a molecular perspective on the differential effects and mechanisms of NPs-NOR composite pollution, providing new insights into the assessment of in vitro responses to composite pollutant exposure.

An Atomic and Molecular Insight into How PFOA Reduces α-Helicity, Compromises Substrate Binding, and Creates Binding Pockets in a Model Globular Protein

Per- and polyfluoroalkyl substances (PFAS) pose significant health risks due to their widespread presence in various environmental and biological matrices. However, the molecular-level mechanisms underlying the interactions between PFAS and biological constituents, including proteins, carbohydrates, lipids, and DNA, remain poorly understood. Here, we investigate the interactions between a legacy PFAS, viz. perfluorooctanoic acid (PFOA), and the milk protein β-lactoglobulin (BLG) obtained using a combination of experimental and computational techniques. Circular dichroism studies reveal that PFOA perturbs the secondary structure of BLG, by driving a dose-dependent loss of α-helicity and alterations in its β-sheet content. Furthermore, exposure of the protein to PFOA attenuates the on-rate constant for the binding of the hydrophobic probe 8-anilino-1-naphthalene sulfonic acid (ANS), suggesting potential functional impairment of BLG by PFOA. Steered molecular dynamics and umbrella sampling calculations reveal that PFOA binding leads to the formation of an energetically favorable novel binding pocket within the protein, when residues 129-142 are steered to unfold from their initial α-helical structure, wherein a host of intermolecular interactions between PFOA and BLG's residues serve to insert the PFOA into the region between the unfolded helix and beta-sheets. Together, the data provide a novel understanding of the atomic and molecular mechanism(s) by which PFAS modulates structure and function in a globular protein, leading to a beginning of our understanding of altered biological outcomes.

Regulation mechanisms of ferric ions release from iron-loaded transferrin protein caused by nano-sized polystyrene plastics-induced conformational and structural changes

Currently, the binding of iron-binding protein transferrin (TF) with NPs and their interaction mechanisms have not been completely elucidated yet. Here, we probed the conformation-dependent release of Fe ions from TF induced by nano-sized polystyrene plastics (PS-NPs) using dialysis, ICP-MS, multi-spectroscopic techniques, and computational simulation. The results showed that the release of free Fe ions from TF was activated after PS-NPs binding, which displayed a clear dose-effect correlation. PS-NPs binding can induce the unfolding and loosening of polypeptide chain and backbone of TF. Alongside this we found that the TF secondary structure was destroyed, thereby causing TF protein misfolding and denaturation. In parallel, PS-NPs interacted with the chromophores, resulting in the occurrence of fluorescence sensitization effects and the disruption of the surrounding micro-environment of aromatic amino acids. Also, the binding of PS-NPs induced the formation of new aggregates in the PS-NPs-TF system. Further simulations indicated that PS-NPs exhibited a preference for binding to the hinge region that connects the C-lobe and N-lobe, which is responsible for the Fe ions release and structural alterations of TF. This finding provides a new understanding about the regulation of the release of Fe ions of iron-loaded TF through NPs-induced conformational and structural changes.

Ferric ions release from iron-binding protein: Interaction between acrylamide and human serum transferrin and the underlying mechanisms of their binding

Acrylamide (ACR) is a surprisingly common chemical due to its widespread use in industry and various other applications. However, its toxicity is a matter of grave concern for public health. Even worse, ACR is frequently detected in numerous fried or baked carbohydrate-rich foods due to the Maillard browning reaction. Herein, this study intends to delineate the underlying molecular mechanisms of Fe ions released from iron-binding protein transferrin (TF) after acrylamide binding by combining multiple methods, including multiple complementary spectroscopic techniques (UV-Vis, fluorescence, and circular dichroism spectroscopy), isothermal titration calorimetry, ICP-MS measurements, and modeling simulations. Results indicated that free Fe was released from TF only under high-dose ACR exposure (>100 μM). Acrylamide binding induced the loosening and unfolding of the backbone and polypeptide chain and destroyed the secondary structure of TF, thereby leading to protein misfolding and denaturation of TF and forming a larger size of TF agglomerates. Of which, H-binding and van der Waals force are the primary driving force during the binding interaction between ACR and TF. Further modeling simulations illustrated that ACR prefers to bind to the hinge region connecting the C-lobe and N-lobe, after that it attaches to the Fe binding sites of this protein, which is the cause of free Fe release from TF. Moreover, ACR interacted with the critical fluorophore residues (Tyr, Trp, and Phe) in the binding pocket, which might explain such a phenomenon of fluorescence sensitization. The two binding sites (Site 2 and Site 3) located around the Fe (III) ions with low-energy conformations are more suitable for ACR binding. Collectively, our study demonstrated that the loss of iron in TF caused by acrylamide-induced structural and conformational changes of transferrin.

Unraveling the Compositional and Molecular Features Involved in Lysozyme-Benzothiazole Derivative Interactions

In this work we present a computational analysis together with experimental studies, focusing on the interaction between a benzothiazole (BTS) and lysozyme. Results obtained from isothermal titration calorimetry, UV-vis, and fluorescence were contrasted and complemented with molecular docking and machine learning techniques. The free energy values obtained both experimentally and theoretically showed excellent similarity. Calorimetry, UV-vis, and 3D/2D-lig-plot analysis revealed that the most relevant interactions between BTS and lysozyme are based on a predominance of aromatic, hydrophobic Van der Waals interactions, mainly aromatic edge-to-face (T-shaped) π-π stacking interactions between the benzene ring belonging to the 2-(methylthio)-benzothiazole moiety of BTS and the aromatic amino acid residue TRP108 of the lysozyme receptor. Next, conventional hydrogen bonding interactions contribute to the stability of the BTS-lysozyme coupling complex. In addition, mechanistic approaches performed using elastic network models revealed that the BTS ligand theoretically induces propagation of allosteric signals, suggesting non-physiological conformational flexing in large blocks of lysozyme affecting α-helices. Likewise, the BTS ligand interacts directly with allosteric residues, inducing perturbations in the conformational dynamics expressed as a moderate conformational softening in the α-helices H1, H2, and their corresponding β-loop in the lysozyme receptor, in contrast to the unbound state of lysozyme.

Effects of dietary dosage forms of copper supplementation on growth, antioxidant capacity, innate immunity enzyme activities and gene expressions for juvenile Litopenaeus vannamei

The experiment was conducted to evaluate the effects of different dietary dosage forms of copper supplementation on growth performance, hematological characteristics, antioxidant capacity, immune responses and gene expressions related to innate immune of juvenile Pacific white shrimp Litopenaeus vannamei. Three isonitrogenous and isolipidic diets were formulated to contain three dosage forms of copper: copper sulfate (Diet I-Cu), copper sulfate + copper amino acid complex (1: 1, Diet M-Cu) and copper amino acid complex from Availa^®Cu100 (Diet Availa-Cu), respectively. 360 Pacific white shrimp juveniles (initial weight 1.86 ± 0.03 g) were randomly allocated in 12 tanks corresponding to quadruplicate tanks of the three dietary treatments, and the 8-week feeding trail was conducted. The results indicated that percent weight gain (PWG) and specific growth rate (SGR) in shrimp fed M-Cu diet were significantly higher than that fed I-Cu diet. Survival, feed efficiency (FE), protein efficiency ratio (PER) of shrimp were not significantly different between all treatment groups. High contents of total protein (TP) and glucose (GLU) were found in shrimp fed the diet containing M-Cu, whereas contents of cholesterol (CHOL) and triacylglycerol (TAG) in shrimp fed M-Cu diet were significantly lower than that in I-Cu diet group. In hemolymph, shrimp fed M-Cu diet had high activities of phenoloxidase (PO), alkaline phosphatase (ALP) and acid phosphatase (ACP). While, Cu/Zn superoxide dismutase (Cu/Zn SOD), ceruloplasmin (CP) and lysozyme (LZM) in hemolymph were not significantly affected by different dietary dosage forms of copper. High activities of Cu/Zn SOD, ALP, ACP and LZM in hepatopancreas were observed in shrimp fed M-Cu diet. Shrimp fed diet supplemented with Availa-Cu showed a significantly higher gene expression levels of Cu/Zn sod, alp, acp and lzm in hepatopancreas than that fed I-Cu diet. This study indicated that copper amino acid complex was more effective than copper sulfate to improve growth performance and enhance antioxidant ability and innate immune system.

Characterizing the binding interactions of PFOA and PFOS with catalase at the molecular level

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) have effects on human health by inducing oxidative stress and catalase (CAT) is a vital enzyme involved in protection against oxidative damage. The interactions of PFOA and PFOS with CAT were investigated by using biophysical methods including spectroscopic techniques, molecular docking and enzyme activity measurements. UV-visible, circular dichroism (CD) and resonance light scattering (RLS) spectroscopy results showed that the structure and conformation of CAT were changed by PFOA and PFOS. PFOA could loosen and unfold the skeleton of CAT but PFOS affected the microenvironment around the aromatic amino acid residues and heme groups. Both PFOA and PFOS altered the secondary structure of CAT by decreasing α-helix and increasing β-sheet content. The size of CAT was smaller and CAT became dispersed when it was bound by perfluorinated compounds (PFCs). Furthermore, enzyme activity test showed that PFOS decreased the activity of CAT because the binding site of PFOS was close to the active center of CAT, but PFOA had little effect on the activity because PFOA bound at the surface of the enzyme. These results indicated that PFCs could damage the structures and conformations of CAT but the changes were not always related to the activity and function of CAT.

Interactions of perfluorooctanoic acid and perfluorooctanesulfonic acid with serum albumins by native mass spectrometry, fluorescence and molecular docking

The binding information of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) with bovine and human serum albumins was investigated and characterized in details by using a combination method of electrospray ionization mass spectrometry (ESI-MS), fluorescence, circular dichroism (CD) and molecular docking (MD). The ESI-MS analysis revealed that maximally eight PFOA or PFOS molecules could bind to serum albumins at high mole ratios of PFOA/PFOS. Association constants were measured by ESI-MS and suggested that PFOS had a better binding affinity than PFOA. PFOA and PFOS were likely to bind with serum albumins in more than one pocket. The CD data demonstrated that binding of PFOA and PFOS could change the conformation of serum albumins with decreasing α-helix content, which may affect the protein physiological function. The phenomenon of protein fluorescence quenching by the binding of PFOA and PFOS indicated that the hydrophobic pocket proximate to Trp 214 in human serum albumin might be one of the dominated binding sites. This assumption was further confirmed by MD simulation. Consistent to ESI-MS observation, MD results also displayed a stronger binding affinity of PFOS than PFOA according to the calculated binding free energy, which is probably ascribed to one more hydrogen bond formed in the PFOS-bound protein complexes.

Binding of copper to lysozyme: Spectroscopic, isothermal titration calorimetry and molecular docking studies

Although copper is essential to all living organisms, its potential toxicity to human health have aroused wide concerns. Previous studies have reported copper could alter physical properties of lysozyme. The direct binding of copper with lysozyme might induce the conformational and functional changes of lysozyme and then influence the body's resistance to bacterial attack. To better understand the potential toxicity and toxic mechanisms of copper, the interaction of copper with lysozyme was investigated by biophysical methods including multi-spectroscopic measurements, isothermal titration calorimetry (ITC), molecular docking study and enzyme activity assay. Multi-spectroscopic measurements proved that copper quenched the intrinsic fluorescence of lysozyme in a static process accompanied by complex formation and conformational changes. The ITC results indicated that the binding interaction was a spontaneous process with approximately three thermodynamical binding sites at 298K and the hydrophobic force is the predominant driven force. The enzyme activity was obviously inhibited by the addition of copper with catalytic residues Glu 35 and Asp 52 locating at the binding sites. This study helps to elucidate the molecular mechanism of the interaction between copper and lysozyme and provides reference for toxicological studies of copper.

Investigation of the effects of nanoAg on the enzyme lysozyme at the molecular level

The toxicity of nanoAg may be explained by its surrounding smaller lysozyme, and its release of silver ions.

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

Key binding sites influencing lysozyme activity when interacting with CdCl₂.

Probing the toxic mechanism of Ag⁺ with lysozyme

Silver (Ag) is widely used in human activities, which provides possibilities to distribute in organisms and tissues, resulting in harmful effects on human health. In this work, lysozyme was chosen as the target molecule to study the mechanism of toxic interactions between Ag(+) and protein using fluorescence emission spectra, synchronous fluorescence spectra, UV-vis absorption spectra, circular dichroism (CD) spectra, isothermal titration calorimetry (ITC), and enzyme activity assay. The results of fluorescence emission and synchronous fluorescence showed that there were interactions between Ag(+) and lysozyme by eliminating the inner filter effect (IFE). Data from UV-vis spectra indicated that the frame structure of lysozyme became looser with Ag(+) existent, while the micro-environment of aromatic amino acid residues did not show any significant alteration. CD results suggested that the secondary structure of lysozyme presented a decrease in α-helix contents with the increasing amount of Ag(+). ITC results showed Ag(+) can spontaneously bind with lysozyme through hydrogen bonding and van der Waals forces with one binding site (Ka=1.93×10(6)). The lysozyme activity was inhibited by Ag(+) according to the enzyme activity assay, revealing that Ag(+) bound to lysozyme at the active site which resulted in inhibition of lysozyme activity. This work showed that Ag(+) can cause damages to the structure and function of lysozyme.

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.

Assessing the potential toxic effect of one persistent organic pollutant: non-covalent interaction of dicofol with the enzyme trypsin

Because of the widespread concern that persistent organic pollutants (POPs) may be adversely affecting the health of humans, reliable assessing their toxic effects is urgently needed. We selectively study the interaction between dicofol (DCF) and trypsin by steady state and time resolved fluorescence quenching measurements and UV-visible absorption spectroscopy under physiological conditions as well as applying molecular docking method to establish the interaction model. The fluorescence results indicate DCF can spontaneously form a complex with trypsin mainly by hydrogen bond with only one binding site, which had been validated in molecular docking. The conformational change of trypsin was proved by UV-visible absorption and synchronous fluorescence spectroscopy indicating a red shift of carbonyl absorption peak. All the results indicated DCF had potential toxic effects on both the structure and activity of the enzyme trypsin and the effects enhanced with the increasing concentration of DCF.

New insights into the characterization of the binding of tetracycline analogues with lysozyme: a biophysical study

Tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC) are the most common members of the widely used veterinary drug tetracyclines, the residue of which in the environment can enter human body, being potentially harmful. Lysozyme is a monomeric protein widely distributed in the nature including human beings, having many physiological and pharmaceutical functions. The aim of this study was to examine the interaction of lysozyme with the three tetracyclines (TC, CTC and OTC) through spectroscopic and molecular modeling methods. The experimental results revealed that all the three tetracyclines (TCs) can interact with lysozyme with one binding site to form TCs-lysozyme complex, mainly through electrostatic forces with the affinity order: CTC>TC>OTC. The binding of TCs can cause conformational and some microenvironmental changes of lysozyme. Furthermore, molecular docking was applied to define the specific binding sites, the results of which show that all the three TCs can bind into lysozyme cleft and interact with the key active-site residues Glu 35 or Asp 52, resulting in competitive inhibition of lysozyme activity. The accurate and full basic data in the work is beneficial to clarifying the binding mechanism of TCs with lysozyme in vivo.

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.

Spectroscopic studies on the interactions between 3,4-dihydropyrimidin-2(1H)-ones and bovine serum albumin

The interactions between 3,4-dihydropyrimidin-2(1H)-ones (DHPM) and bovine serum albumin (BSA) were investigated by fluorescence and ultraviolet spectroscopy under imitated physiological conditions. The experimental results showed that all DHPM could form complexes with BSA. Static quenching and non-radiation energy transfer are the main reasons leading to the fluorescence quenching. The binding constants (K(A)) and the number of binding sites (n) were calculated. According to Förster theory of non-radiation energy transfer, the binding distances (r) between BSA and DHPM are less than 7 nm. The relationship between different aryl groups in pyrimidine ring and the binding ability of DHPM with BSA is preliminarily discussed. Moreover, the synchronous fluorescence spectra indicated that the conformation of BSA has not been changed.

Interaction of perfluorooctanoic acid with human serum albumin

Background

Recently, perfluorooctanoic acid (PFOA) has become a significant issue in many aspects of environmental ecology, toxicology, pathology and life sciences because it may have serious effects on the endocrine, immune and nervous systems and can lead to embryonic deformities and other diseases. Human serum albumin (HSA) is the major protein component of blood plasma and is called a multifunctional plasma carrier protein because of its ability to bind an unusually broad spectrum of ligands.

Results

The interaction of PFOA with HSA was investigated in the normal physiological condition by equilibrium dialysis, fluorospectrometry, isothermal titration calorimetry (ITC) and circular dichroism (CD). The non-covalent interaction is resulted from hydrogen bond, van der Waals force and hydrophobic stack. PFOA binding to HSA accorded with two-step binding model with the saturation binding numbers of PFOA, only 1 in the hydrophobic intracavity of HSA and 12 on the exposed outer surface. The interaction of PFOA with HSA is spontaneous and results in change of HSA conformation. The possible binding sites were speculated.

Conclusion

The present work suggested a characterization method for the intermolecular weak interaction. It is potentially useful for elucidating the toxigenicity of perfluorochemicals when combined with biomolecular function effect, transmembrane transport, toxicological testing and the other experiments.