Binding studies for the interaction between hazardous organophosphorus compound phosmet and lysozyme: Spectroscopic and In-silico analyses

Unraveling the binding behavior of the antifouling biocide 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one with human serum albumin: Multi-spectroscopic, atomic force microscope, computational simulation, and esterase activity

As a marine antifouling biocide, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) exhibited high toxicity to marine organisms. This study investigated the interaction between DCOIT and human serum albumin (HSA) using several spectroscopic techniques combined with computer prediction methods. The UV-vis absorption spectra, Stern-Volmer constant (KSV) and fluorescence resonance energy transfer (FRET) results indicated that DCOIT caused static quenching of HSA fluorescence. The ΔG°, ΔH° and ΔS° values were -31.03 ± 0.17 kJ·mol-1, -133.54 ± 0.88 kJ·mol-1 and -348.46 ± 2.86 J.mol-1·K-1, respectively, suggesting that van der Waals forces and hydrogen bonds governed the spontaneous formation of the complex. Synchronous fluorescence and circular dichroism (CD) spectroscopy observed the burial of Trp residues within HSA and the unfolding of HSA secondary structure induced by DCOIT. Three-dimensional (3D) fluorescence and Atomic Force Microscopy (AFM) further detected DCOIT-induced loosening of HSA peptide chain structure. Site displacement experiments indicated that DCOIT binding at site I of HSA. Computational predictions indicated that hydrophobic interactions were also essential in the complex. The increased RMSD, Rg, SASA, and RMSF confirmed that DCOIT weakened the stability and compactness of HSA, rendering residues more flexible. Lastly, esterase activity assays demonstrated that DCOIT inhibited esterase activity and interfered with the human detoxification process.

Thermodynamic and functional changes of alpha-chymotrypsin after interaction with gallic acid

In the present study, the interaction mechanism between gallic acid (GA) and α-Chymotrypsin (α-CT) was investigated by employing a series ofspectroscopic methods, computational docking and molecular dynamic (MD) simulation. Fluorescence spectra analysis indicated the formation of a stable complex between GA and α-CT, where the quenching of the fluorescence emission was predominantly characterized by a static mechanism. TheCA obtained binding constants for the α-CT-GA complex were in the order of 103 M-1, indicating the moderate binding affinity of GA for α-CT. The corresponding CD findings showed that the interaction between GA and α-CT resulted in an alteration of the protein's secondary structure. The findings of the enzyme activity investigation clearly showed that the presence of GA led to a notable decline in the enzymatic activity of α-CT, highlighting GA's function as an effective inhibitor for α-CT. The molecular docking simulations revealed the optimal binding site for the GA molecule within the α-CT structure and MD simulations confirmed the stability of the α-CT-GA complex. This research expands our comprehension regarding the behavior of enzymes in the presence of small-molecule ligands and opens avenues for food safety.

Probing the toxic effect of chlorpyrifos as an environmental pollutant on the structure and biological activity of lysozyme under physiological conditions

The pervasive use of pesticides like chlorpyrifos (CPY) has been associated with deleterious effects on biomolecules, posing significant risks to environmental integrity, public health, and overall ecosystem equilibrium. Accordingly, in this study, we investigated the potential binding interaction between the well-conserved enzyme, lysozyme (LSZ), and CPY through various spectroscopic techniques and molecular modeling. The UV-vis absorption and fluorescence experiments confirmed the complex formation and static quenching of the intrinsic fluorescence intensity. LSZ revealed a singular binding site for CPY, with binding constants around 105 M-1 across different temperature ranges. Analysis of thermodynamic parameters showed the spontaneous nature of the complexation process, while also revealing the pivotal role of hydrophobic interactions in stabilizing the LSZ-CPY system. According to circular dichroism and Fourier transform infrared studies, CPY binding changed the secondary structure of LSZ by boosting α-helix presence and reducing the levels of β-sheet and β-turn content. Further, CPY decreased the stability and activity of LSZ. Computational docking delineated the specific and highly preferred binding site of CPY within the structure of LSZ. Molecular dynamic simulation indicated the enduring stability of the LSZ/CPY complex and revealed structural modifications in the LSZ after binding with CPY. This research provides a detailed understanding of the intermolecular dynamics between CPY and LSZ, concurrently elucidating the molecular-level implications for the potential hazards of pesticides in the natural environment.

The toxicity assessment of phosmet on development, reproduction, and gene expression in Daphnia magna

The use of pesticides to control pests, weeds, and diseases or to regulate plant growth is indispensable in agricultural production. However, the excessive use of these chemicals has led to significant concern about their potential negative impacts on health and the environment. Phosmet is one such pesticide that is commonly used on plants and animals against cold moth, aphids, mites, suckers, and fruit flies. Here, we investigated the effects of phosmet on a model organism, Daphnia magna using acute and chronic toxicity endpoints such as lethality, mobility, genotoxicity, reproduction, and gene expression. We performed survival experiments in six-well plates at seven different concentrations (0.01, 0.1, 1, 10, 25, 50, 100 μM) as well as the control in three replicates. We observed statistically significant mortality rates at 25 µM and above upon 24 h of exposure, and at 1 µM and above following 48 h of exposure. Genotoxicity analysis, reproduction assay and qPCR analysis were carried out at concentrations of 0.01 and 0.1 μM phosmet as these concentrations did not show any lethality. Comet assay showed that exposure to phosmet resulted in significant DNA damage in the cells. Interestingly, 0.1 μM phosmet produced more offspring per adult compared to the control group indicating a hormetic response. Gene expression profiles demonstrated several genes involved in different physiological pathways, including oxidative stress, detoxification, immune system, hypoxia and iron homeostasis. Taken together, our results indicate that phosmet has negative effects on Daphnia magna in a dose- and time-dependent manner and could also induce lethal and physiological toxicities to other aquatic organisms.

Evidence for paraquat-pepsin interaction: In vitro and silico study

The use of the herbicide paraquat (PQ) has raised concerns about potential environmental consequences due to its toxicity and persistence in the environment. Considering the affinity of dangerous compounds to biological molecules, it is necessary to know their binding properties. This article focuses on the behavior of the pepsin enzyme following its contact with paraquat poison, and the interaction between paraquat and pepsin has been investigated in laboratory conditions and simulated physiological conditions using multispectral techniques. Fluorescence experiments showed that PQ uses a static method to quench pepsin's intrinsic fluorescence. By causing structural damage to pepsin, PQ may be detrimental as it alters its conformational function based on FT-IR spectroscopy. The coupling reaction is a spontaneous process caused by hydrogen bonding and van der Waals forces according to the analysis of the thermodynamic parameters of each system at three different temperatures. The molecular structure of pepsin changes when it binds to PQ. Also, the results showed that PQ is a pepsin inhibitor that changes the function of the enzyme.

Comparative study of dietary phenols with Tartary buckwheat protein (2S/13S): impact on structure, binding sites and functionality of protein

BACKGROUND

This research was to investigate the interaction mechanism between 2S albumin and 13S globulin (2S and 13S, the most important storage proteins in Tartary buckwheat seeds) and three phenols (rutin, quercetin and myricetin) regarding the structural and antioxidant properties of their complexes.

RESULTS

There are differences in the binding affinity of phenols for 2S and 13S. Rutin had a higher binding affinity for 2S, myricetin had a higher binding affinity for 13S, and 13S exhibited a higher affinity toward phenols than did 2S. Binding with phenols significantly changed the secondary and tertiary structures of 2S and 13S, decreased the surface hydrophobic value and enhanced the antioxidant capacity. Molecular docking and isothermal titration calorimetry showed that the binding processes were spontaneous and that there were hydrogen bonds, hydrophobic bonds and van der Waals force interactions between phenols and proteins.

CONCLUSION

These findings could provide meaningful guidance for the further application of buckwheat protein complex. © 2023 Society of Chemical Industry.

Binding interactions of Vildagliptin with pepsin: A multi-spectroscopic and in-silico approach and a comparative account with metformin

Vildagliptin (VDG) and Metformin (Met) belong to a class of dipeptidylpeptidase-4 (DPP-4) inhibitor and biguanide, respectively and used for the management of diabetes mellitus type II (DMTII). Both the drugs are orally available which leads to various side effects due to its oral ingestion. Occurrence of these side effects might be due to some interactions with pepsin at a molecular level. Therefore, in order to investigate these interactions, multi-spectroscopic and in-silico techniques have been extensively studied to identify the binding characteristics of VDG with pepsin. Fluorescence data suggested that the quenching is due to dynamic and static mechanism and static was dominant one. However, fluorescence and UV-Vis spectroscopic measurement analysis suggested that VDG tends to associate with pepsin, via ground-state complex formation. Fluorescence study revealed the binding-constant value which was found to be 0.559 × 103 M-1 at 298.15 K that is non-covalent in nature. VDG-pepsin complex shows exothermic and spontaneous binding as confirmed by the calculated values of ΔH, ΔS, and ΔG, are majorly caused by van der Waals forces and H-bonding interactions. CD spectra of pepsin in presence of VDG confirmed post binding conformational change. Enzyme-activity assay showed that activity of pepsin was decreased by upto 28 %. FRET analysis suggested that energy transfer efficiency is negligible for VDG-pepsin interaction. In-silico analysis reveals that H-bonding and electrostatic negative forces are the significant driving forces involved in the interaction of VDG and pepsin.

Unravelling the molecular interactions of phenyl isothiocyanate and benzoyl isothiocyanate with human lysozyme: Biophysical and computational analyses

Phenyl isothiocyanate and benzoyl isothiocyanate are the phytochemicals present in the Brassicaceae family. They have antibacterial, antiapoptotic and antifungal properties. Protein-small molecule interaction studies are done to assess the changes in structure, dynamics, and functions of protein and to decipher the binding mechanism. This study is based on the comparative binding of PT and BT with human lysozyme using in vitro and computational techniques. UV, fluorescence emission, and FRET spectra gave insight into the complex formation, quenching mechanism, and binding parameters. Both PT and BT quenched the intrinsic fluorescence of Lyz by a static quenching mechanism. Synchronous, 3D fluorescence and CD spectroscopy substantiated conformational and microenvironmental alterations in the Lyz. The metal ions and β-cyclodextrin had a pronounced effect on the binding strength of Lyz-PT and Lyz-BT complexes. Accessible surface area analysis was determined to characterise the amino acid residue packing. Molecular docking further validated the wet lab experimental results.

Structural alterations and inhibition of lysozyme activity upon binding interaction with rotenone: Insights from spectroscopic investigations and molecular dynamics simulation

The pervasive employment of pesticides such as rotenone on a global scale represents a substantial hazard to human health through direct exposure. Therefore, exploring the interactions between such compounds and body macromolecules such as proteins is crucial in comprehending the underlying mechanisms of their detrimental effects. The present study aims to delve into the molecular interaction between rotenone and lysozyme by employing spectroscopic techniques along with Molecular dynamics (MD) simulation in mimicked physiological conditions. The binding interaction resulted in a fluorescence quenching characterized by both dynamic and static mechanisms, with static quenching playing a prominent role in governing this phenomenon. The analysis of thermodynamic parameters indicated that hydrophobic interactions primarily governed the spontaneous bonding process. FT-IR and circular dichroism findings revealed structural alternations of lysozyme upon complexation with rotenone. Also, complexation with rotenone declined the biological activity of lysozyme, thus rotenone could be considered an enzyme inhibitor. Further, the binding interaction substantially decreased the thermal stability of lysozyme. Molecular docking studies showed the binding location and the key residues interacting with rotenone. The findings of the spectroscopic investigations were confirmed and accurately supported by MD simulation studies.

Structural changes and anti-hepatocellular carcinoma activity of interferon-γ after interaction with sinensetin

Exploring the interaction of small molecules with therapeutic proteins can provide useful information about development of ligand-protein complexes as synergistically therapeutic platforms. In this study, the interaction of sinensetin with human interferon gamma (IFNγ) was evaluated experimentally and theoretically. Also, the synergistic effects of IFNγ- sinensetin complex on the inhibition of hepatocellular carcinoma HepG2 cell proliferation were assessed by cell viability and quantitative real time PCR assays. It was realized that sinensetin interacts with IFNγ through a static quenching mechanism and hydrophobic forces mediated by presence of Lys55 and Lys58 amino acid residues in the binding site were the main contributing forces in the spontaneous formation of IFNγ-sinensetin complex. Also, the interaction of sinensetin with IFNγ did not induce a significant change in the secondary and tertiary structure of the protein. Cellular assays revealed a synergistic effect of sinensetin on IFNγ -triggered anticancer action in HepG2 cells through overexpression of caspase-3 mRNA and protein. In conclusion, this study may hold great promise for the development of potential ligand- protein complexes for therapeutic purposes.

Molecular Recognition Study toward the Mitochondrial Electron Transport Chain Inhibitor Mubritinib and Human Serum Albumin

The ability to bind plasma proteins helps in comprehending relevant aspects related to the pharmacological properties of many drugs. Despite the vital role of the drug mubritinib (MUB) in the prophylaxis of various diseases, its interaction with carrier proteins still needs to be clarified. The present work focuses on the interaction between MUB and Human serum albumin (HSA), investigated by employing multispectroscopic, biochemical, and molecular docking approaches. The results reveal that MUB has quenched HSA intrinsic fluorescence (following a static mechanism) by attaching very close (r = 6.76 Å) and with moderate affinity (Kb ≈ 104 M-1) to the protein site I (mainly by H-bonds, hydrophobic and Van der Waals forces). On one side, the HSA-MUB interaction has been accompanied by a slight disturbance in the HSA chemical environment (around the Trp residue) and protein secondary structure modifications. On another side, MUB competitively inhibits HSA esterase-like activity, which is very similar to other Tyrosine kinase inhibitors, and evidence that protein functional alterations have been triggered by MUB interaction. In summary, all of the presented observations can shed light on diverse pharmacological factors associated with drug administration.

Multispectroscopic studies of binding interaction of phosmet with bovine hemoglobin

Phosmet is a phthalimide derived broad spectrum organophosphate pesticide which is vastly used across the globe to protect several ornamental or horticulture crops. The toxicity of phosmet is of utmost concern because of its direct effect on the nervous system of the victim after exposure. The mechanism of phosmet toxicity was explored by the interaction with the model blood protein which is hemoglobin. Bovine Hemoglobin (BHb) is a major protein of red blood cells (RBCs) that plays an important role in the exchange of gases for respiration and ensures adequate oxygen supply to tissues for oxygenation. In the current study, the interaction of BHb with phosmet was revealed using various spectroscopic techniques. Circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) studies of BHb in the presence of phosmet showed secondary structural changes in the protein post binding, Fluorescence study shows the involvement of the dynamic quenching predominantly, Van't Hoffs thermodynamic study showed negative enthalpy value and free energy change and negative entropy change that revealed the involvement of hydrogen bonding and van der Waal forces predominantly further revealing spontaneous nature of binding interaction. The shift in Ultraviolet-visible spectra also revealed the nature of the interaction. In-silico study finally deduced the involvement of hydrogen bonding and polar interaction. The study inferred the moderate interaction of BHb with phosmet.

Elucidation on inhibition and binding mechanism of bovine liver catalase by nifedipine: multi-spectroscopic analysis and computer simulation methods

Nifedipine (NDP), a dihydropyridine calcium antagonist, is widely used for the treatment of hypertension and angina pectoris. Catalase is a key antioxidant enzyme that is closely relevant to the level of reactive oxygen species (ROS) in vivo. Here, the research explored the effects of NDP on the conformation and catalytic function of bovine liver catalase (BLC) through enzymatic reaction kinetic techniques, multi-spectroscopic analysis and computer simulation method. Kinetic studies clarified that the NDP debased the activity of BLC by non-competitive inhibition mechanism. Based on the data of trials, it was a static quenching mechanism that functioned in the quenching of intrinsic fluorescence of BLC. The binding constant value was (4.486 ± 0.008) × 10⁴ M^-1 (298 K) and BLC had one binding site for NDP. Tyr was prone to be exposed more to a hydrophilic environment in wake of a shift in fluorescence value. The binding reaction of BLC to NDP caused the conformational alteration of BLC, which in turn led to increase of the α-helix and decline of β-sheet contents. Furthermore, several amino acids residues interacted with NDP by means of van der Waals forces, whereas Gln397, Asn368, Gln371, Asn384 and Pro377 formed several Hydrogen Bonds with NDP.

Characterization of interactions of montelukast sodium with human serum albumin: multi-spectroscopic techniques and computer simulation studies

The interaction mechanism of montelukast sodium and HSA was characterized using spectroscopic and computer methods.