Conformational alterations induced by novel green 16-E2-16 gemini surfactant in xanthine oxidase: Biophysical insights from tensiometry, spectroscopy, microscopy and molecular modeling

Lysozyme binding with amikacin and levofloxacin studied by tritium probe, fluorescence spectroscopy and molecular docking

Lysozyme complexes with amikacin and levofloxacin were studied by spectroscopy approaches as well as using a tritium probe. Tritium was used as a labeling agent to trace labeled compound concentration in a system of two immiscible liquids and in the atomic form to determine the possible position of the binding site. Co-adsorption of protein and drug at the liquid-liquid interface was analyzed by scintillation phase method that allowed us to directly determine the amount of protein and drug in the mixed adsorption layer. Also, tensiometric measuring of the interfacial tension was used for calculation of binding parameters accordingly to Fainerman model. The treatment of complexes with atomic tritium followed by trypsinolysis and analysis of tritium distribution in the lysozyme peptides reveals the binding sites, binding energies in which were analyzed using molecular docking. Formation of complexes with amikacin and levofloxacin preserves secondar structure of protein. However, the formation of complex with amikacin leads to the almost total loss of the enzymatic activity of lysozyme and the redshift of the maximum on the lysozyme fluorescence band. A slight decrease in the distribution coefficient of lysozyme in the presence of amikacin assumes that the complex has higher hydrophilicity in comparison to lysozyme without additives. The most favorable for binding were the positions of the active centers that included amino acids Asp52 and Glu35, as well as in the vicinity of peptide His15-Arg21, with the participation of amino acids Tyr20, Arg14. In the case of levofloxacin, the formation of lysozyme-ligand complex in aqueous solution is possible without changing the microenvironment of the active center of the protein. Binding of levofloxacin to the active center of the enzyme was the most favorable, but Asp52 and Glu35 that are responsible for the enzymatic activity of lysozyme, were not affected.

Study on the interaction mechanism between luteoloside and xanthine oxidase by multi-spectroscopic and molecular docking methods

Gout is an inflammatory joint disease caused by urate crystal deposition, which is associated with hyperuricemia. Gout will take place when the uric acid accumulates. Xanthine oxidase (XO) is a crucial enzyme in the formation of uric acid. Inhibiting XO is one of the means to ameliorate gout. Luteoloside is a kind of natural flavonoid, which has an excellent prospect for relieving gout. But there are few reports on the interaction mechanism between luteoloside and XO currently. In this study, the interaction mechanism between luteoloside and XO was explored using spectroscopy and molecular docking. The fluorescence spectroscopy results indicated that luteoloside could make the intrinsic fluorescence of XO quenched, and the binding constant between luteoloside and XO was (1.85 ± 0.22) × 10³  L mol^-1 at 298 K. The synchronous fluorescence spectroscopy results showed that the absorption peaks of Tyr and Trp shifted blue, and the hydrophobicity of the microenvironment increased. Moreover, CD spectra showed that α-helix of XO decreased, β-sheet and β-turn increased after adding luteoloside. The results of molecular docking analysis showed that XO could combine with luteoloside through hydrogen bonds and hydrophobic force. The results indicated that luteoloside could remarkably interact with XO. Insights into the interaction mechanism provide a necessary basis for the search for low-toxic natural products as targets of XO. HIGHLIGHTS: Luteoloside and xanthine oxidase was a strong binding mode and had only one binding site. Luteoloside could cause α-helix reduced, β-sheet and β-turn increased, and change the secondary structure of XO. The binding between luteoloside and xanthine oxidase was a spontaneous process. The main binding force was hydrophobic force between luteoloside and xanthine oxidase.

Experimental techniques to study protein-surfactant interactions: New insights into competitive adsorptions via drop subphase and interface exchange

Protein surfactant (PS) interactions is an essential topic for many fundamental and technological applications such as life science, nanobiotechnology processes, food industry, biodiesel production and drug delivery systems. Several experimental techniques and data analysis approaches have been developed to characterize PS interactions in bulk and at interfaces. However, to evaluate the mechanisms and the level of interactions quantitatively, e.g., PS ratio in complexes, their stability in bulk, and reversibility of their interfacial adsorption, new experimental techniques and protocols are still needed, especially with relevance for in-situ biological conditions. The available standard techniques can provide us with the basic understanding of interactions mainly under static conditions and far from physiological criteria. However, detailed measurements at complex interfaces can be formidable due to the sophisticated tools required to carefully probe nanometric phenomena at interfaces without disturbing the adsorbed layer. Tensiometry-based techniques such as drop profile analysis tensiometry (PAT) have been among the most powerful methods for characterizing protein's and surfactant's adsorption layers at interfaces via measuring equilibrium and dynamic interfacial tension and dilational rheology analysis. PAT provides us with insightful data such as kinetics and isotherms of adsorption and related surface activity parameters. However, the data analysis and interpretation can be challenging for mixed protein-surfactant solutions via standard PAT experimental protocols. The combination of a coaxial double capillary (micro flow exchange system) with drop profile analysis tensiometry (CDC-PAT) is a promising tool to provide valuable results under different competitive adsorption/desorption conditions via novel experimental protocols. CDC-PAT provides unique experimental protocols to exchange the droplet subphase in a continuous dynamic mode during the in-situ analysis of the corresponding interfacial adsorbed layer. The contribution of diffusion/convection mechanisms on the kinetics of the adsorption/desorption processes can also be investigated using CDC-PAT. Here, firstly, we review the commonly available techniques for characterizing protein-surfactant interactions in the bulk phase and at interfaces. Secondly, we give an overview for applications of the coaxial double capillary PAT setup for investigations of mixed protein-surfactant adsorbed layers and address recently developed protocols and analysis procedures. Exploring the competitive sequential adsorption of proteins and surfactants and the reversibility of pre-adsorbed layers via the subphase exchange are the particular experiments we can perform using CDC-PAT. Also the sequential and simultaneous competitive adsorption/desorption processes of some ionic and nonionic surfactants (SDS, CTAB, DTAB, and Triton) and proteins (bovine serum albumin (BSA), lysozyme, and lipase) using CDC-PAT are discussed. Last but not least, the fabrication of micro-nanocomposite layers and membranes are additional applications of CDC-PAT discussed in this work.

Interaction of eugenol with xanthine oxidase: Multi spectroscopic and in silico modelling approach

Eugenol, a major component in clove has various biological activities. The current study focused to the binding potential of eugenol with Xanthine oxidase (XO) were evaluated using multi spectroscopic techniques and in silico docking studies. Xanthine oxidase, a superoxide generating enzyme, catalyses hypoxanthine and xanthine to uric acid. An excessive uric acid and superoxide anion radical in our body causes many serious clinical complications. The activity and the structural alterations can be a significant method to reduce this kind of risk factors. The results obtained from the fluorescence titration exhibited the interactions initiated by a static quenching mechanism. The ultraviolet (UV), fourier-transform infrared (FTIR), circular dichroism (CD) spectroscopic analysis of eugenol bind with XO indicated the secondary structural alteration in XO. Docking studies showed molecular level interaction of eugenol with the amino acid residues of Thr 1010, Phe 914, Phe 1009, Leu 1014, Phe 1009, Val 1011, Arg 880, Ala 1078, Glu 802, Leu 648and Leu 873 which residing at the catalytic active site of the XO. These results inferred that the eugenol can interact with XO in a remarkable manner and these findings provide a supporting data for the XO inhibition studies to propose a new lead compound.

Molecular Interaction of Amino Acid-Based Gemini Surfactant with Human Serum Albumin: Tensiometric, Spectroscopic, and Molecular Docking Study

Binding effect and interaction of N,N'-dialkyl cystine based gemini surfactant (GS); 2(C₁₂Cys) with human serum albumin (HSA) were systematically investigated by the techniques such as surface tension measurement, UV-visible spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking studies. The surface tension measurement exhibited that HSA shifted the critical micelle concentration of the 2(C₁₂Cys) GS to the higher side that confirms the complex formation among 2(C₁₂Cys) GS and HSA which was also verified by UV-visible, fluorescence, and CD spectroscopy. Increase in the concentration of 2(C₁₂Cys) GS increases the absorption of the HSA protein but has a reverse effect on the fluorescence intensity. The analysis of UV-visible study with the help of a static quenching method showed that the value acquired for the bimolecular quenching constant (k _q) quenches the intrinsic fluorescence of the HSA protein. Synchronous fluorescence spectrometry declared that the induced-binding conformational changes in HSA and CD results explained the variations in the secondary arrangement of the protein in presence of 2(C₁₂Cys) GS. The present study revealed that the interaction between 2(C₁₂Cys) GS and HSA is important for the preparation and properties of medicines. Molecular docking study provides insight into the specific binding site of 2(C₁₂Cys) GS into the sites of HSA.

Understanding the fate of human serum albumin upon interaction with edifenphos: Biophysical and biochemical approaches

Edifenphos (EDF), an important organophosphate fungicide used in agriculture, is a great threat to human health and environment. To assess the toxicity of EDF at the level of protein molecule, the effect of EDF on human serum albumin (HSA) was investigated by biophysical and biochemical approaches. EDF-HSA complex is formed as a result of static quenching as revealed by the intrinsic fluorescence analysis. Thermodynamic analysis of the binding data suggests involvement of hydrophobic interactions in EDF-HSA complex formation, which is in line with molecular docking results. Moreover, thermodynamic parameters of binding between EDF and HSA suggest entropy-driven spontaneous interaction, presumably dominated by hydrophobic forces. Further, binding site of EDF seems to have been located within sub-domain IIA of HSA. EDF binding to HSA decreases its alpha helical content as analyzed by CD spectra. Marked micro-environmental changes around tryptophan/tyrosine residues in HSA upon EDF binding were recorded via three-dimensional fluorescence spectroscopy. Substantial release of protein carbonyl from HSA as a result of EDF treatment suggested involvement of ROS in EDF induced protein damage. This work is expected to provide some leads toward EDF induced toxicity in humans and would be helpful in reinforcing the check on food safety.

Bio-physicochemical analysis of ethylene oxide-linked diester-functionalized green cationic gemini surfactants

A novel series of oxy-diester-functionalized gemini surfactants (Cm-E2O-Cm) were synthesized and a comprehensive analysis of their biophysicochemical properties was carried out.

New insights into binding interaction of novel ester-functionalized m-E2-m gemini surfactants with lysozyme: a detailed multidimensional study

Different binding patterns of m-E2-m (12-E2-12 and 14-E2-14) surfactants to HEWL.