Sodium dodecyl sulfate rearranges the conformation of transferrin and attenuates its iron-binding capacity

Sodium dodecyl sulfate (SDS), an anionic surfactant used in many cleaning and hygiene products, is known for its dermal and respiratory toxicity. However, how this surfactant influences the iron dynamics within the body and the mechanism is unknown. We explored the interaction between SDS and human transferrin (HTF), focusing on the effects on iron-binding capacity and structural changes. Results revealed that SDS exposure led to a significant release of iron from HTF in a dose-dependent manner, changing its structure and reducing the iron-binding ability. Spectroscopic analyses showed that the protein secondary structure and skeleton, as well as the micro-environment of aromatic amino acids of HTF, were destroyed after SDS binding. Isothermal titration calorimetry (ITC) results (ΔG, ΔS, and ΔH were -40.1 kcal·mol-1, 0.16 kcal·mol-1·K-1, and 10.1 kcal·mol-1, respectively) indicated a spontaneous and hydrophobic interaction with one strong binding site. Molecular docking identified the preferred binding sites, emphasizing hydrophobic forces (with the hydrophobic tail) and hydrogen bonds (with the hydrophilic head) as the primary driving forces, which aligns with the ITC results. Overall, this comprehensive analysis sheds light on the intricate interplay between SDS and HTF, providing insights into potential health risks associated with SDS exposure.

Anti-Bacterial and Anti-Biofilm Activities of Essential Oil from Citrus reticulata Blanco cv. Tankan Peel Against Listeria monocytogenes

In recent years, plant essential oils have been confirmed as natural inhibitors of foodborne pathogens. Citrus reticulata Blanco cv. Tankan peel essential oil (CPEO) showed anti-Listeria monocytogenes (LM) activities, and this study investigated the associated mechanisms by using high-resolution electron microscope, fluorescence spectrometer, flow cytometer, potentiometer, and transcriptome sequencing. The results showed that CPEO restrained LM growth at a minimum inhibitory concentration of 2% (v/v). The anti-LM abilities of CPEO were achieved by disrupting the permeability of the cell wall, damaging the permeability, fluidity, and integrity of the cell membrane, disturbing the membrane hydrophobic core, and destroying the membrane protein conformation. Moreover, CPEO could significantly inhibit the LM aggregation from forming biofilm by reducing the extracellular polymeric substances' (protein, polysaccharide, and eDNA) production and bacterial surface charge numbers. The RNA sequencing data indicated that LM genes involved in cell wall and membrane biosynthesis, DNA replication and repair, quorum sensing and two-component systems were expressed differently after CPEO treatment. These results suggested that CPEO could be used as a novel anti-LM agent and green preservative in the food sector. Further studies are needed to verify the anti-LM activities of CPEO in real food.

Differential response of catalase to As (III) and As (V): Potential molecular mechanism under valence effect

Arsenic (As) is the most prolific contaminant in food, triggering arseniasis primarily via contaminated rice and drinking contaminated water. However, toxicological data for arsenite (As (III)) and arsenate (As (V)) on antioxidant enzyme catalase (CAT) at molecular level is shortage. The interaction mechanism of As (III) and As (V) with CAT was investigated using enzyme activity detection, multi-spectroscopic techniques, isothermal titration calorimetry and computational simulations. Results indicated As (III) and As (V) induced protein skeleton relaxation, secondary structure transformation, fluorescence sensitization and particle alteration of CAT, particularly As (III). Moreover, As (III)/As (V) bound to CAT through hydrogen bonding and hydrophobic. As (III) and As (V) contacted with core residues His 74, Asn 147 and His A74, Trp A357, respectively, thereby inhibiting CAT activity. Overall, As (III) is more aggressive against the structure and physiological function of CAT than As (V). Our findings enhance the understanding of health risk related to dietary As exposure.

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.

Anti-browning and antibacterial dual functions of novel hydroxypyranone-thiosemicarbazone derivatives as shrimp preservative agents: Synthesis, bio-evaluation, mechanism, and application

To develop new shrimp preservative agents with dual functions of anti-browning and antibacterial, thirteen hydroxypyranone-thiosemicarbazone derivatives were prepared according to molecular hybridization. Thereinto, compound 7j (IC₅₀ = 1.99 ± 0.19 μM) shown the strongest anti-tyrosinase activity and was about twenty-three folds stronger than kojic acid (45.73 ± 4.03 μM). The anti-tyrosinase mechanism of 7j was illustrated through enzyme kinetic, copper ion chelating ability, fluorescence quenching, ultraviolet spectrum, AFM analysis, and molecular docking study. On the other hand, antibacterial assay and time-kill kinetics analysis confirmed that 7j also had good antibacterial activity against V. parahaemolyticus (MIC = 0.13 mM). PI uptake test, SDS-PAGE, and fluorescence spectrometry analysis proved that 7j can affect the bacterial cell membrane. Finally, the shrimp preservation and safety study indicated that 7j has dual effects of inhibiting bacterial growth and preventing enzyme browning, and can be applied to the preservation of fresh shrimp.

Cytotoxicity and Oxidative Stress Effects of Indene on Coelomocytes of Earthworm (Eisenia foetida): Combined Analysis at Cellular and Molecular Levels

Indene (IND) is a kind of important aromatic hydrocarbon that is extracted from coal tar and has important applications in industry and biology. In the process of production and utilization, it is easy to enter the soil and produce toxic effects on the soil or organisms. The earthworm is an important organism in the soil. The toxicity of indene on earthworm coelomocytes is rarely studied, and the oxidative stress effects of IND on earthworm coelomocytes remain unclear. In this study, coelomocytes from earthworms and antioxidant enzymes were selected as the research targets. In addition, IND caused oxidative stress, and its related toxic effects and mechanisms were systematically studied and evaluated at the cellular and molecular levels. The results showed that IND destroyed the redox balance in earthworm coelomocytes, and the large accumulation of reactive oxygen species (ROS) significantly inhibited the activities of the antioxidant system, including superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH), and caused lipid peroxidation and membrane permeability changes, resulting in a decrease in cell viability to 74.5% of the control group. At the molecular level, IND was bound to SOD by the arene-H bond, and the binding constant was 4.95 × 10³. IND changed the secondary structure of the SOD and led to a loosening of the structure of the SOD peptide chain. Meanwhile, IND caused SOD fluorescence sensitization, and molecular simulation showed that IND was mainly bound to the junction of SOD subunits. We hypothesized that the changes in SOD structure led to the increase in SOD activity. This research can provide a scientific basis for IND toxicity evaluation.

Scrutinizing the interaction between metribuzin with glutathione reductase 2 from Arabidopsis thaliana: insight into the molecular toxicity in agriculture

As one of the triazine herbicides with widespread usage in agriculture, metribuzin exerted nonnegligible hazardous effects on plants via excessive accumulation of reactive oxygen species and destruction of antioxidant enzymes, but the underlying harmful mechanism of metribuzin-induced oxidative damage to plants has never been exploited. Here, Arabidopsis thaliana glutathione reductase 2 (AtGR2) was employed as the biomarker to evaluate the adverse impacts of metribuzin on plants. The fluorescence intensity of AtGR2 was decreased based on the static quenching mechanism with the prediction of a single binding site toward metribuzin, and the complex formation was presumed to be mainly impelled by hydrogen bonding and van der Waals forces from the negative ΔH and ΔS. In addition, the loosened and unfolded skeleton of AtGR2 along with the increased hydrophilicity around the tryptophan residues were investigated. Besides, the glutathione reductase activity of AtGR2 was also destroyed due to structural and conformational changes. At last, the severe inhibiting growth of Arabidopsis seedling roots was discovered under metribuzin exposure. Hence, the evaluation of the molecular interaction mechanism of AtGR2 with metribuzin will establish valuable assessments of the toxic effects of metribuzin on plants.

Transferrin Enhances Neuronal Differentiation

Although transferrin (Tf) is a glycoprotein best known for its role in iron delivery, iron-independent functions have also been reported. Here, we assessed apoTf (aTf) treatment effects on Neuro-2a (N2a) cells, a mouse neuroblastoma cell line which, once differentiated, shares many properties with neurons, including process outgrowth, expression of selective neuronal markers, and electrical activity. We first examined the binding of Tf to its receptor (TfR) in our model and verified that, like neurons, N2a cells can internalize Tf from the culture medium. Next, studies on neuronal developmental parameters showed that Tf increases N2a survival through a decrease in apoptosis. Additionally, Tf accelerated the morphological development of N2a cells by promoting neurite outgrowth. These pro-differentiating effects were also observed in primary cultures of mouse cortical neurons treated with aTf, as neurons matured at a higher rate than controls and showed a decrease in the expression of early neuronal markers. Further experiments in iron-enriched and iron-deficient media showed that Tf preserved its pro-differentiation properties in N2a cells, with results hinting at a modulatory role for iron. Moreover, N2a-microglia co-cultures revealed an increase in IL-10 upon aTf treatment, which may be thought to favor N2a differentiation. Taken together, these findings suggest that Tf reduces cell death and favors the neuronal differentiation process, thus making Tf a promising candidate to be used in regenerative strategies for neurodegenerative diseases.

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.

Discrepancy of apoptotic events in mouse hepatocytes and catalase performance: Size-dependent cellular and molecular toxicity of ultrafine carbon black

The diversification of the production process and application of ultrafine carbon black (UFCB), one of the nanomaterials, make the difference in particle sizes that exposed to environment. Currently, few size-dependent toxicity studies of UFCB pay attention to targeted effects on detoxification organs. And there is a research gap in the size-dependent molecular toxicity of UFCB. Based on this, mouse hepatocytes and catalase (CAT) were used as targeted receptors for UFCB size-dependent cellular and molecular toxicity studies. Results indicate that UFCB_13 nm induced higher ROS and lipid peroxidation levels. And the cell viability decreased to 22.5%, which is sharp contrast to UFCB_50 nm (45.3%) and UFCB_95 nm (55.1%). Mitochondrial dysfunction and a 25.2% early apoptosis rate are the further manifestation of the stronger cytotoxicity of UFCB_13 nm. At the molecular level, the exposure of UFCB with better dispersity resulted in more significant changes in the CAT backbone and secondary structure, fluorescence sensitization and enzyme function inhibition. The combined experiments show that the cellular uptake and dispersity of UFCB are the dominating factors for the discrepancy in size-dependent cellular and molecular toxicity, respectively. This study provides a theoretical basis for the necessary circumvention and substitution of UFCB in engineering applications.

Placental cadmium, placental genetic variations, and birth size

BACKGROUND

Maternal cadmium (Cd) burden has been associated with offspring birth size measures, yet associations of placental Cd with birth size are less clear. Further, the role of genetics in these associations has not been examined. We investigated associations of placental Cd with birth size and placental genotypes. We also examined the potential role of placental genotypes as modifiers of placental Cd and birth size associations.

METHODS

Participants were 490 mother-child pairs from the Omega and Placenta Microarray studies based in Seattle, WA. Placental Cd was measured using Agilent 7500 ICP-MS. The birth size was characterized using birth weight (BW), ponderal index (PI), and head circumference (HC). Eleven placental single nucleotide polymorphisms (SNPs) related to metal transport, growth regulation, endocrine response, and cell signaling were genotyped. Adjusted multivariable linear regression models were used to examine overall and sex-specific associations of placental Cd with birth size (BW, PI and HC), as well as associations of placental genotypes with placental Cd. Effect modification of placenta Cd and birth size associations by placental SNPs was examined using interaction terms and stratified analyses.

RESULTS

Mean maternal age was 33.6 years (SD = 4.4). Mean and median placental Cd levels were 4.0 ng/g tissue (SD = 2.7 ng/g tissue) and 3.6 ng/g (IQR 2.5 - 5.2 ng/g), respectively. Overall, compared with infants in the lowest quartile for placental Cd, infants in the second (ß = -102.8 g, 95% CI: -220.7, 15.1), third (ß = -83.2 g, 95% CI: -199.3, 32.9) and fourth (ß = -109.2 g, 95% CI: -225.4, 7.1) quartiles had lower BW, though associations were not statistically significant (all p-values > .05, trend p-value = .11). Among male infants, infants in the second (ß = -203.3 g, 95% CI: -379.7, -27.0) and fourth quartiles (ß = -198.3 g, 95% CI: -364.2, -32.5) had lower BW compared with those in the first quartiles (p-values < .05, trend p-value = .08). Similar relationships were not observed among female infants, though infant sex-placental Cd interaction terms were not significant. Similarly, male, but not female, infants had marginally significant positive associations between placental Cd and ponderal index (trend p-value = .06). The minor rs3811647 allele of the placental transferrin gene (NCBI Gene ID: 7018) was associated with an increase in Cd among all infants (p-value = .04). We did not find differences in associations of placental Cd with birth size markers among infants stratified by rs3811647 genotype.

CONCLUSIONS

Placental Cd was inversely associated with BW among male infants. The rs3811647 SNP of the transferrin gene was associated with placental Cd.

Exploring the toxic interactions between Bisphenol A and glutathione peroxidase 6 from Arabidopsis thaliana

As primary industrial raw material, the widespread usage of bisphenol A (BPA) has resulted in sustained release and accumulation in the environment. Besides its endocrine-disrupting character, BPA was reported to generate excessive reactive oxygen species (ROS). However, the potential toxic mechanisms of the BPA-induced oxidative damage to plants were poorly understood. In this study, glutathione peroxidase 6 from Arabidopsis thaliana (AtGPX6) was regarded as biomarker to investigate the toxic effects of BPA on plants by multi-spectroscopic techniques and molecular docking method. Firstly, BPA effectively quenched the intrinsic fluorescence of AtGPX6 via static quenching mechanism, and a single binding site of AtGPX6 towards BPA was presumed. Moreover, the binding force was mainly driven by van der Waals forces and hydrogen bonding based on the negative values of ΔH⁰ and ΔS⁰, which was consistent with the molecular docking result. In addition, the conformational changes of AtGPX6 accompanied with the enhancement of the hydrophilicity around the tryptophan residues upon the combination with BPA, were evaluated through the combination of the fluorescence, UV-visible absorption and Circular dichroism (CD) spectroscopy. Finally, the inhibitory impact on the development of Arabidopsis seedling roots was observed under BPA exposure. Therefore, the exploration of the molecular mechanism of AtGPX6 with BPA would provide valuable assessments on the toxic effects of BPA on plants.

Investigating the interaction of CdTe quantum dots with plasma protein transferrin and their interacting consequences at the molecular and cellular level

This study investigated the interacting mechanism of CdTe quantum dots (QDs) with typical plasma protein transferrin (TF) as well as the impact of the formation of QDs-TF complex on the structure of TF and the cytotoxicity of mouse primary kidney cells. Dialysis experiments and cell viability assays revealed that the formation of QDs-TF complex reduced the contents of Cd released from CdTe QDs and thus counteracted the cytotoxicity of CdTe QDs. The assay of isothermal titration calorimetry found that CdTe QDs complexed with TF majorly through hydrophobic interaction. Multi-spectroscopic measurements showed that CdTe QDs caused the loosening of polypeptide chain, the changes of secondary and tertiary structures as well as the attenuated aggregation of TF molecule. Moreover, these structural and conformational changes were attributed to the nano-effects of CdTe QDs rather than the released Cd. This study is of great significance for fully evaluating the biocompatibility of Cd-QDs and comprehensively understanding the mechanism of Cd-QDs toxicity at the molecular and cellular level.

Extraction of Pb(II) from wheat samples via dual-frequency ultrasound-assisted enzymatic digestion and the mechanisms of its interactions with wheat proteins

A novel dual-frequency ultrasound-assisted enzymatic digestion (DUED) technique was used to extract Pb(II) from certified reference materials (CRMs) of wheat flour. Following this, the interactions of Pb(II) with wheat proteins were investigated to provide evidence for the selection of enzyme species. The results showed that the simultaneous use of α-amylase and flavourzyme resulted in the recovery of 97.9% of Pb(II) in 6 min under a 40 kHz ultrasonic bath combined with a 20 kHz ultrasonic probe. The exopeptidase activity of the flavourzyme was found to be the main contributor to the extraction of Pb(II) from the CRMs. Additionally, the proposed method exhibited a low detection limit (8.2 ng/g) and high recoveries of real samples (93.4%-112.2%) with RSD less than 7.33%. Furthermore, the oxygen-containing groups of wheat proteins, the nitrogen-containing groups of albumins and globulins, and the sulfur-containing groups of gliadins and glutenins were found to offer coordination sites for Pb(II).

Exploring the influence of silver and lead on structure and function of xylanase: spectroscopic and calorimetric methods

Soil contamination with heavy metal could induce the alteration of soil ecological environments, and soil enzyme activities are sensitive indicators for the soil toxicology. Xylanase is one of predominant soil enzymes related to carbon nitrogen cycle. In this work, we explored the underlying mechanisms for conformational and enzymatic activity alterations of xylanase after silver and lead exposure at molecular level with systematical measurements including multiple spectroscopic methods, isothermal titration calorimetry, and enzymatic activity. Both silver and lead could loosen and unfold the skeleton of xylanase with the quenching of endogenous fluorescence. Silver interacted with xylanase forming larger-size aggregations through Van der Waals forces and hydrogen bonding, while lead interacted with xylanase forming larger-size aggregations through hydrophobic force. Silver and lead induced an obvious loss (67.1 and 56.31%) of the xylanase enzymatic activity, but silver has a greater impact on xylanase than that of lead. The xylanase enzymatic activity significantly decreased due to the conformational alterations. The negative effect of silver exposure on xylanase structure and function was more prominent than that of lead.

Glutathione peroxidase 6 from Arabidopsis thaliana as potential biomarker for plants exposure assessment to di-(2-ethylhexyl) phthalate

As a most abundant plasticizer, Di-(2-ethylhexyl) phthalate (DEHP) has been widely used in agriculture with an associated potential toxicity to many species including plants via the production of the excessive reactive oxygen species (ROS). However, the potential toxic mechanisms of the plasticizer DEHP-induced oxidative damage to plants remain unknown. The antioxidant enzyme glutathione peroxidase has been suggested as biomarkers to reflect over excessive oxidative stress. In this study, the effect of DEHP on AtGPX6 was evaluated by multi-spectroscopic techniques and molecular docking method. The fluorescence intensity of AtGPX6 was reduced by the static quenching mechanism upon the addition of DEHP. The predominant forces in complex formation was mainly impelled by hydrogen bonding and Van der Waals forces based on the negative ΔH and ΔS, which was in accordance with the molecular docking results. In addition, the secondary structural changes resulted from the complex formation were investigated in presence of different amounts of DEHP by the combination of fluorescence, UV-vis absorption and Circular dichroism spectra, which revealed the loosening and unfolding of the framework of AtGPX6 accompanied with the enhancement of the hydrophilicity around the tryptophan residues. The exploration of the interaction mechanism of DEHP with AtGPX6 at molecular level would help to evaluate the toxicity of the plasticizers and forecast the related adverse effects on plants.

Probing the molecular toxic mechanism of lead (II) ions with glutathione peroxidase 6 from Arabidopsis thaliana

Along with non-biodegradability and accumulation in agricultural soil, lead (II) ions exert considerable harmful effects on plants even at trace amount, especially for the oxidative damages elicited by the lead ions-induced excessive reactive oxygen species (ROS). The glutathione peroxidases were reported to be correspondent with the oxidative stress induced by heavy metals. However, limited data are available about the potential hazardous mechanisms of the lead ions-induced oxidative damage to plants at molecular level. In this study, the harmful impacts of lead ions on Arabidopsis thaliana glutathione peroxidase 6 (AtGPX6) were assessed based on multi-spectroscopic measurements and molecular docking study. The characteristic fluorescence of AtGPX6 was quenched by lead ions with static mechanism at different temperatures. AtGPX6 exhibits a single binding site with lead ions, and then the complex formation was mainly driven by hydrogen bonding interaction and van der Waals forces on account of the negative ΔH and ΔS. The secondary structural changes were observed from the synchronous fluorescence, UV-visible absorption and Circular dichroism spectra, which led to loosen and unfold of the protein framework accompanied by the incremental hydrophobicity around the vicinity of the tryptophan residues. Therefore, this work illustrates the detailed binding mode between lead (II) ions and glutathione peroxidase 6 from Arabidopsis thaliana and the toxic effects on antioxidative defense system induced by lead ions at molecular level.

Binding mechanism of maltol with catalase investigated by spectroscopy, molecular docking, and enzyme activity assay

Maltol is a flavor additive that is widely used in the daily diet of humans, and its biosafety attention is concomitantly increasing. Catalase (CAT) is an antioxidant enzyme to maintain homeostasis in the tissue's environment of human body and protect cells from oxidative damages. The adverse effects of maltol to CAT activity within mouse hepatocytes as well as the structural and functional changes of CAT on molecular level were investigated by multiple spectroscopy techniques, enzyme activity experiments, and molecular docking. Results suggested that when the maltol concentrations reached to 8 × 10^-5 mol L^-1 , the viability of hepatocytes decreased to 93%, and CAT activity was stimulated by maltol to 111% than the control group after exposure for 24 hours. Changes in CAT activity on molecular level were consistent with those on cellular level. The fluorescence quenching of CAT by maltol was static with the forming of maltol-CAT complex. Moreover, ultraviolet-visible (UV-visible) absorption, synchronous fluorescence, and circular dichroism (CD) spectra reflected that the presence of maltol caused conformational change of CAT and made the CAT molecule skeleton loose and increased α-helix of CAT. Maltol mainly bound with CAT through hydrogen bond, and binding site that is near the heme ring in the enzyme activity center did not interact with its main amino acid residues. This study explores the combination between maltol and CAT, providing references for evaluating health damages caused by maltol.

Characterization on the toxic mechanism of two fluoroquinolones to trypsin by spectroscopic and computational methods

Ciprofloxacin (CPFX) and enrofloxacin (ENFX), two of the most widely used fluoroquinolones (FQs), pose a great threat to humans and the ecosystem. In this study, the toxic mechanisms between the two FQs and trypsin were evaluated by means of multiple spectroscopic methods, as well as molecular docking. During the fluorescence investigations, both FQs quenched the intrinsic fluorescence of trypsin effectively, which was due to the formation of moderately strong complexes (mainly through van der Waals forces and hydrogen bonds). The binding of two FQs not only caused the conformational and micro-environmental changes of trypsin, but also changed its molecular activity; shown by the UV-Visible absorption spectroscopy, synchronous fluorescence spectroscopy, and functional tests. The established methods in this work can help to comprehensively understand the transport of FQs in the human body.

Responses of catalase and superoxide dismutase to low-dose quantum dots on molecular and cellular levels

With the wider application of cadmium-containing quantum dots (Cd-QDs) in biomedical fields, it is easier for people to be exposed. Studies have suggested that Cd-QDs could release cadmium ion and induce oxidative effects due to the disruption of redox equilibrium. Antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD), play an important role in organisms to resist the negative impact of exogenous substances. Molecular mechanisms of antioxidant enzymes with Cd-QDs remain unclear, however. In this study, structural and functional changes of CAT and SOD have been investigated under low dose Cd-QDs exposure. Cell viability, malondialdehyde (MDA) level, CAT and SOD activities were influenced by Cd-QDs in hepatocytes of mice. To further investigate the responses of CAT and SOD to Cd-QDs, multiple spectroscopic, calorimetric and activity measurements were carried out. Similar interaction patterns were observed that result in interaction force, structural and functional changes: Cd-QDs combine with CAT and SOD through hydrophobic forces; Intrinsic fluorescence of proteins was statically quenched by Cd-QDs and new complexes were formed; Also, the skeleton and secondary structure (with α-helix decrease) of CAT and SOD was influenced. Taken together, we suggest that Cd-QDs chosen in this study induce oxidative stress effects to hepatocytes but have not caused serious oxidative stress damage at concentrations below 10 μg/mL. MPA-CdSe/ZnS QDs caused the lowest level of oxidative stress which is associated with the induction of antioxidant proteins. This paper presents responses of CAT and SOD to low-dose Cd-QDs, and provides a reference for evaluating health damages caused by Cd-QDs.

Exploring the conformational changes in fibrinogen by forming protein corona with CdTe quantum dots and the related cytotoxicity

This study describes synthesis of N‑acetyl‑l‑cysteine-capped CdTe quantum dots (QDs) and investigates their interaction with plasma protein fibrinogen (FIB) and the structural changes of FIB. It is shown that the interaction of QDs with FIB is a spontaneous process and the major driving forces are van der Waals forces and hydrogen bonds. Multi-spectroscopic measurements show that the intrinsic fluorescence of FIB was quenched and secondary and tertiary structures were altered due to the interaction with QDs. In addition, the aggregation state of FIB was altered in the presence of QDs. Furthermore, the formed complexes of FIB with QDs reduced the cytotoxicity of QDs. The coating of FIB on QDs could lower intracellular QDs uptake and therefore result in less released cadmium ions and ROS productions. This study, therefore, might be helpful to the comprehensive understanding of QDs toxicity and provide evidence for assessing the safe application of nanoparticles.

Molecular mechanism study on the interactions of cadmium (II) ions with Arabidopsis thaliana glutathione transferase Phi8

Accumulation of cadmium ions may result in adverse effects on plant due to the oxidative stress via destructions of antioxidants and antioxidant enzymes. As the core component of the glutathione antioxidant system, glutathione S-transferases (GSTs) have been reported as biomarkers for evaluating the metal-induced oxidative damage to plants, but the potential toxicity and underlying toxic molecular mechanisms remain unknown. This article investigated the molecular interactions of cadmium ions with Arabidopsis thaliana glutathione S-transferase phi8 (AtGSTF8) by multi-spectroscopic techniques and enzyme activity measurements. The intrinsic fluorescence of AtGSTF8 was quenched statically upon the addition of cadmium ions accompanied with the complex formation and structural and conformational alterations from multiple spectroscopic measurements, resulting in deconstructed protein skeleton and microenvironmental alterations around the Tyr and Trp residues. A single binding site was predicted for AtGSTF8 towards cadmium ions and the van der Walls interactions and hydrogen bonds are the major driving forces of the interaction. In addition, the transferase activity changes of AtGSTF8 upon the addition of cadmium ions have been observed. The implementation of this work helps to clarify the mechanism of oxidative damage and antioxidant enzymes response induced by heavy metal accumulation in plant at molecular level.

Spectroscopic characterization, calorimetric study and molecular docking to evaluate the bioconjugation of maltol with hemoglobin

Maltol, a food additive, is extensively used in our daily life. To date, its biological safety is still debated. In this article, binding interaction of maltol with bovine hemoglobin (BHb), an important functional protein, was studied by molecular docking research and spectroscopic and calorimetric measurements. We found that maltol could cause structural changes of BHb. By interacting with Glu 101 (1.27 Å) and Lys 104 (2.49 Å) residues, maltol changed the cavity structure and induced a microenvironment change around tryptophan (Trp) residue. Thermodynamic parameters obtained from isothermal titration calorimetry (ITC) measurement showed that hydrophobic forces were the main forces existing in this system. The association constant of K (8.0 ± 3.4 × 10⁴  M^-1 ) shows the mild ligand-protein binding for maltol with BHb. The α-helix amount in BHb increased (59.6-62.6%) with different concentrations of maltol and the intrinsic fluorescence intensity was quenched by maltol, indicating the conformation changes and denaturation of BHb. This work presents the interactions of maltol with BHb at the molecular level and obtains evidence that maltol induces adverse effects to proteins in vitro.

Influence of tobacco smoke on zinc, cadmium, iron, iron-binding proteins, and low-weight anti-oxidant status in pregnancy

Pregnancy and tobacco smoking (TS) each can cause increases in reactive oxygen species (ROS) production; this, in turn, can lead to disorders in iron management and disruption of the pro- and anti-oxidant balance. The aim of the study was to analyze the influence of TS and Cd on Fe, Zn, and anti-oxidant levels (i.e. glutathione [GSH], metallothionein [MT]) in the blood of pregnant women. The study reported here evaluated 110 blood samples from pregnant women in their 1st, 2nd and 3rd trimester. Concentrations of ferritin and transferrin were measured in the serum; Zn, Fe and cotinine in the plasma, that of Cd in whole blood, that for glutathione in red blood cell lysates, and levels of metallothionein both in the plasma and in lysates prepared from isolated erythrocytes. The results indicated there was a decrease in Zn and increase in Cd and metallothionein levels in pregnant women smokers as compared to in nonsmoking counterparts. Differences in intracellular MT concentration were noted both in smoking and nonsmoking women during pregnancy while there were no changes in extracellular MT level. A decline in circulating ferritin and a rise in transferrin during pregnancy was observed in all groups. Based on the results, it was concluded that exposure to TS-associated xenobiotics like Cd could result in higher MT levels in erythrocytes and in pregnant smokers, the major anti-oxidant mechanism that is in place is one being mediated by MT and not by reduced GSH.

Molecular mechanism investigation on the interactions of copper (II) ions with glutathione peroxidase 6 from Arabidopsis thaliana

Accumulation of copper (II) ions in plant leads to the excessive reactive oxygen species (ROS) which attributes to the depletion of the antioxidants in the cell and destruction to antioxidant enzymes. The antioxidant enzyme glutathione peroxidase has been used as biomarkers to reflect metal-induced oxidative stress. However, the underlying toxic mechanisms of the copper ions(II)-induced oxidative damage to plants remain unknown. In the work, a detailed molecular interaction of copper (II) ions with Arabidopsis thaliana glutathione peroxidase 6 (AtGPX6) in relation with poisonous effects of exposure to heavy metal was investigated by multiple spectroscopic techniques. The intrinsic fluorescence of AtGPX6 was quenched upon the addition of copper (II) ions by the combination of static and dynamic quenching mechanisms accompanied by complex formation and conformational changes. A single binding site was revealed for AtGPX6 towards copper ions. The binding process was hydrophobic effect accompanied by positive entropy change and enthalpy change. The secondary structure of AtGPX6 was changed by the addition of copper ions investigated by synchronous fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy and circular dichroism spectroscopy, resulting in loosened and deconstructed protein skeleton and increased hydrophobicity around the Trp residues. This study helps to illuminate the detailed interactions between copper ions and plant glutathione peroxidase and elucidate the destructive mechanism to antioxidative defense system caused by heavy metal exposure at molecular level.

Computational approaches for deciphering the equilibrium and kinetic properties of iron transport proteins

With the advances in three-dimensional structure determination techniques, high quality structures of the iron transport proteins transferrin and the bacterial ferric binding protein (FbpA) have been deposited in the past decade. These are proteins of relatively large size, and developments in hardware and software have only recently made it possible to study their dynamics using standard computational resources. We review computational techniques towards understanding the equilibrium and kinetic properties of iron transport proteins under different environmental conditions. At the level of detail that requires quantum chemical treatments, the octahedral geometry around iron has been scrutinized and it has been established that the iron coordinating tyrosines are in an unusual deprotonated state. At the atomistic level, both the N-lobe and the full bilobal structure of transferrin have been studied under varying conditions of pH, ionic strength and binding of other metal ions by molecular dynamics (MD) simulations. These studies have allowed questions to be answered, among others, on the function of second shell residues in iron release, the role of synergistic anions in preparing the active site for iron binding, and the differences between the kinetics of the N- and the C-lobe. MD simulations on FbpA have led to the detailed observation of the binding kinetics of phosphate to the apo form, and to the conformational preferences of the holo form under conditions mimicking the environmental niches provided by the periplasmic space. To study the dynamics of these proteins with their receptors, one must resort to coarse-grained methodologies, since these systems are prohibitively large for atomistic simulations. A study of the complex of human transferrin (hTf) with its pathogenic receptor by such methods has revealed a potential mechanistic explanation for the defense mechanism that arises in evolutionary warfare. Meanwhile, the motions in the transferrin receptor bound hTf have been shown to disfavor apo hTf dissociation, explaining why the two proteins remain in complex during the recycling process from the endosome to the cell surface. Open problems and possible technological applications related to metal ion binding-release in iron transport proteins that may be handled by hybrid use of quantum mechanical, MD and coarse-grained approaches are discussed.

Interaction of chromium(III) or chromium(VI) with catalase and its effect on the structure and function of catalase: An in vitro study

Heavy metal chromium (Cr) poses a severe health risk to humans via food chain contamination. In this study, the interactions of either trivalent chromium (Cr(III)) or hexavalent chromium (Cr(VI)) with catalase (CAT) were investigated via multi-spectroscopic studies and computational simulations. The fluorescence analysis showed that Cr(III) and Cr(VI) quenched the fluorescence of CAT through a dynamic and a static quenching mechanism, respectively. The binding constant of Cr(VI) with CAT was 3.44×10⁴lmol^-1 at 298K. Other detailed binding characterizations of the Cr(VI)-CAT complex were also obtained using spectra analysis and molecular docking. Synchronous fluorescence, UV-vis and circular dichroism (CD) spectral studies showed that either Cr(III) or Cr(VI) induced conformational changes of CAT, but the degree of influence was different. The response of CAT activity to Cr(III) or Cr(VI) was found to be variable depending on their valence states and concentrations.

Membrane and genomic DNA dual-targeting of citrus flavonoid naringenin against Staphylococcus aureus

Naringenin exerts its antibacterial action by disruption of the cytoplasmic membrane and DNA targeting effects inStaphylococcus aureus.

The influence of maternal smoking on transferrin sialylation and fetal biometric parameters

OBJECTIVES

Transferrin is a glycosylated protein responsible for transporting iron, an essential metal responsible for proper fetal development. Tobacco is a heavily used xenobiotic having a negative impact on the human body and pregnancy outcomes. Aims of this study was to examine the influence of tobacco smoking on transferrin sialic acid residues and their connection with fetal biometric parameters in women with iron-deficiency.

METHODS

The study involved 173 samples from pregnant women, smokers and non-smokers, iron deficient and not. Transferrin sialylation was determined by capillary electrophoresis. The cadmium (Cd) level was measured by atomic absorption and the sialic acid concentration by the resorcinol method.

RESULTS

Women with iron deficiencies who smoked gave birth earlier than non-smoking, non-iron-deficient women. The Cd level, but not the cotinine level, was positively correlated with transferrin sialylation in the blood of iron-deficient women who smoked; 3-, 4-, 5- and 6-sialoTf correlated negatively with fetal biometric parameters in the same group.

CONCLUSION

It has been shown the relationship between Cd from tobacco smoking and fetal biometric parameters observed only in the iron deficient group suggests an additive effect of these two factors, and indicate that mothers with anemia may be more susceptible to Cd toxicity and disturbed fetal development.

The Influence of Tobacco Smoke on Protein and Metal Levels in the Serum of Women during Pregnancy

Background

Tobacco smoking by pregnant women has a negative effect on fetal development and increases pregnancy risk by changing the oxidative balance and microelements level. Smoking affects the concentration, structure and function of proteins, potentially leading to various negative effects on pregnancy outcomes.

Methodology/Principal Findings

The influence of tobacco smoke on key protein fractions in smoking and non-smoking healthy pregnant women was determined by capillary electrophoresis (CE). Concentrations of the proteins α1-antitrypsin, α1-acid glycoprotein, α2-macroglobulin and transferrin were determined by ELISA tests. Total protein concentration was measured by the Biuret method. Smoking status was established by cotinine levels. Cadmium (Cd) and Zinc (Zn) concentrations were determined by flame atomic absorption spectrometry and the Zn/Cd ratio was calculated based on these numbers. Smoking women had a 3.7 times higher level of Cd than non-smoking women. Zn levels decreased during pregnancy for all women. The Zn/Cd ratio was three times lower in smoking women. The differences between the changes in the protein profile for smoking and non-smoking women were noted. Regarding proteins, α1-antitrypsin and α2-macroglobulin levels were lower in the non-smoking group than in the smoking group and correlated with Cd levels (r = -0.968, p = 0.032 for non-smokers; r = −0.835, p = 0.019 for smokers). Zn/Cd ratios correlated negatively with α1-, α2- and β-globulins.

Conclusions/Significance

Exposure to tobacco smoke increases the concentration of Cd in the blood of pregnant women and may lead to an elevated risk of pregnancy disorders. During pregnancy alter concentrations of some proteins. The correlation of Cd with proteins suggests that it is one of the causes of protein aberrations.