Interaction of Cetyltrimethylammonium Bromide and Its Gemini Homologue Bis(cetyldimethylammonium)butane Dibromide with Xanthine Oxidase

Inhibition of porphyra polysaccharide on xanthine oxidase activity and its inhibition mechanism

Xanthine oxidase (XO) is a purine catabolic enzyme related to hyperuricemia and gout. Porphyra polysaccharide (PP) is a kind of sulfated polysaccharide with potent biological activity. Herein, the interaction mechanism between PP and XO was studied by enzyme kinetics and multi-spectroscopy methods for the first time. Inhibition kinetics assay showed that PP reversibly inhibited XO activity in a mixed competitive manner with an IC₅₀ of 10.53 ± 0.69 mg/ml. Fluorescence titration studies and thermodynamic parameter calculations revealed that PP could spontaneously bind to XO through hydrophobic interactions, with a class of binding site. Circular dichroism analysis demonstrated that PP induced secondary structure rearrangement and conformational change of XO. Molecular docking further revealed that PP inserted into the hydrophobic cavity of XO, occupying the catalytic center, leading to the inhibition of XO activity. This study may provide new insights into the inhibitory mechanism of PP as a promising XO inhibitor.

Activity of Polyphenoloxidase in red Fuji Apples Promoted with Cationic Surfactant – Role of Surfactant Structure

In this study, we observed the activity of polyphenoloxidase (PPO) in red Fuji apples in the presence of single-chained surfactants (including cetyl trimethyl ammonium bromide (CTAB), and dodecyl trimethyl ammonium bromide (DTAB)) and gemini surfactants (pentamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide), octamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide, dodecamethylene-α,ω-bis(dodecyl dimethyl ammonium bromide), pentamethylene-α,ω-bis(cetyl dimethyl ammonium bromide), and octamethylene-α,ω-bis(cetyl dimethyl ammonium bromide)). It was found that all these surfactants enhanced the activity of PPO in a wide range of temperature at low content. When PPO was denatured by incubating at high temperature, the surfactants caused reactivation of PPO. Compared to the single-chained surfactants, the gemini surfactants increased PPO activity at a much lower concentration. Moreover, the single-chained surfactant and the gemini surfactant acted together to further increase PPO activity, and the synergistic effect reduced the amount of surfactant used. In addition, the Michaelis-Menten constant for PPO did not change in the presence of the surfactants, suggesting the active site should remain well with the surfactants.

Inhibitory mechanism of xanthine oxidase activity by caffeoylquinic acids in vitro

In this study, the inhibitory activities of eight caffeoylquinic acids (CQAs) against xanthine oxidase (XOD) in vitro were investigated, and the interaction mechanisms between each compound and XOD were studied. HPLC and fluorescence spectra showed that the inhibitory activities of dicaffeoylquinic acids (diCQAs) were higher than that of monocaffeoylquinic acids (monoCQAs), due to the main roles of hydrophobic interaction and hydrogen bond between XOD and diCQAs. Both the binding constant and the lowest binding energy data indicated that the affinities of diCQAs to XOD were stronger than that of monoCQAs. Circular dichroism showed that the structure of XOD was compacted with the increased of α-helix content, resulting in decreased enzyme catalytic activity. Molecular docking revealed that CQAs preferentially bind to the flavin adenine dinucleotide region in XOD. These results provided the mechanisms of CQAs on inhibiting XOD and the further utilization of CQAs as XOD inhibitors to prevent hyperuricemia.

Structural changes in trypsin induced by the bile salts: An effect of amphiphile hydrophobicity

The present study reports the multi-technique results of the interaction of a series of bile salts, sodium cholate (NaC), sodium taurocholate (NaTC), sodium deoxycholate (NaDC), and sodium taurodeoxycholate (NaTDC) with trypsin under the experimental conditions of 25 °C and pH 7.0. The interactions between trypsin and the bile salts were characterized by the surface tension measurements and various spectroscopic techniques like UV-Visible absorption, steady-state fluorescence, and circular dichroism. The results of surface tension measurements reveal a strong interaction of trypsin (50 μM) with the increasing concentration of bile salts, being higher with the bile salt of greater hydrophobicity. The critical aggregation concentration of bile salts in the presence of trypsin (C₁) showed that the bile salts interact strongly with the trypsin in the order of NaTDC > NaDC > NaTC > NaC. UV-visible, steady-state fluorescence, and circular dichroism spectroscopic results confirmed significant unfolding of trypsin due to its interaction with the bile salts, the extent of which followed the same sequence as observed in the surface tension results. It could be concluded that the hydrophobic bile salts that show lower C₁ values and have less delocalized charge, are more effective in unfolding the trypsin. The study would help understand the hydrophobicity-driven unfolding of proteins aided by biological surfactants like bile salts and help devise efficient proteolytic enzyme-based detergent formulations and understand the role of such amphiphiles as antimicrobial agents.

Conformational and solution dynamics of hemoglobin (Hb) in presence of a cleavable gemini surfactant: Insights from spectroscopy, atomic force microscopy, molecular docking and density functional theory

Herein, we have explored the conformational alterations of hemoglobin (Hb) in presence of a cleavable gemini surfactant (C16-C4O2-C16). The concerned surfactant was found to induce significant structural perturbations in Hb. UV-vis spectroscopy, steady-state/time-resolved fluorescence, and other utilized techniques have authenticated the complexation of Hb with the gemini surfactant. CD has demonstrated the alterations in secondary structural elements (α-helicity, β-sheet, β-turn, and random coil) of Hb upon C16-C4O2-C16 addition. Atomic force microscopy (AFM) has revealed the existence of unique star-shaped gemini surfactant microstructures aligned to Hb in a necklace pattern. The ¹H NMR peak broadening and lower delta values hint at the binding of the concerned gemini surfactant to Hb. Molecular docking and DFT calculations have further substantiated the Hb-gemini complex formation and the involvement of electrostatic/hydrophobic forces therein. In future, these results might pave-the-way to construct self-assembled, sustainable, and green surfactant-protein mixtures for their end-use in industrial, engineering, biomedical, drug delivery, gene transfection, and other relevant excipient formulations.

Interaction between 8-methoxypsoralen and trypsin: Monitoring by spectroscopic, chemometrics and molecular docking approaches

8-Methoxypsoralen (8-MOP) is a naturally occurring furanocoumarin with various biological activities. However, there is little information on the binding mechanism of 8-MOP with trypsin. Here, the interaction between 8-MOP and trypsin in vitro was determined by multi-spectroscopic methods combined with the multivariate curve resolution-alternating least squares (MCR-ALS) chemometrics approach. An expanded UV-vis spectral data matrix was analysed by MCR-ALS, the concentration profiles and pure spectra for the three reaction species (trypsin, 8-MOP and 8-MOP-trypsin) were obtained to monitor the interaction between 8-MOP and trypsin. The fluorescence data suggested that a static type of quenching mechanism occurred in the binding of 8-MOP to trypsin. Hydrophobic interaction dominated the formation of the 8-MOP-trypsin complex on account of the positive enthalpy and entropy changes, and trypsin had one high affinity binding site for 8-MOP with a binding constant of 3.81×10⁴Lmol^-1 at 298K. Analysis of three dimensional fluorescence, UV-vis absorption and circular dichroism spectra indicated that the addition of 8-MOP induced the rearrangement of the polypeptides carbonyl hydrogen-bonding network and the conformational changes in trypsin. The molecular docking predicted that 8-MOP interacted with the catalytic residues His57, Asp102 and Ser195 in trypsin. The binding patterns and trypsin conformational changes may result in the inhibition of trypsin activity. This study has provided insights into the binding mechanism of 8-MOP with trypsin.

Reverse micellar extraction of bromelain from pineapple peel--Effect of surfactant structure

Pineapple peel is generally disposed or used as compost. This study was focused on extracting bromelain from pineapple peel by using reverse micelles. It was found that gemini surfactant C12-8-C12·2Br (octamethylene-α,ω-bis(dimethyldodecylammonium bromide)) showed distinctive advantage over its monomeric counterpart DTAB (dodecyl trimethyl ammonium bromide); under optimized condition, the bromelain extracted with C12-8-C12·2Br reverse micelle had an activity recovery of 163% and a purification fold of 3.3, while when using DTAB reverse micelle, the activity recovery was 95% and the purification fold was 1.7. Therefore, the spacer of gemini surfactant should play a positive role in bromelain extraction and may suggest the potential of gemini surfactant in protein separation since it has been so far rarely used in relative experiments or technologies.

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

Herein we report the interaction of a biodegradable gemini surfactant, ethane-1,2-diyl bis(N,N-dimethyl-N-hexadecylammoniumacetoxy) dichloride (16-E2-16) with bovine milk xanthine oxidase (XO), employing tensiometry, fluorescence spectroscopy, UV spectroscopy, far-UV circular dichroism spectroscopy (CD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and computational molecular modeling. Surface tension results depict substantial changes in the micellar as well as interfacial parameters (CMC, ΠCMC, γCMC, Γmax, Amin, ΔGmic° and ΔGads°) of 16-E2-16 gemini surfactant upon XO combination, deciphering the interaction of XO with the gemini surfactant. Fluorescence measurements reveal that 16-E2-16 gemini surfactant causes quenching in the xanthine oxidase (XO) fluorescence spectra via static procedure and the values of various evaluated binding parameters (KSV, Kb, kq, ΔGb° and n) describe that 16-E2-16 effectively binds to XO. Three dimensional fluorescence, 8-anilino-1-naphthalene sulfonic acid (ANS) binding, F1F3 ratio, UV, CD, FTIR, SEM and TEM results delineate changes in the secondary structure of xanthine oxidase. Molecular docking results provide complement to the steady-state fluorescence findings and support the view that quenching occurs due to non-polar environment experienced by aromatic residues of the enzyme. The results of this study can help scientists to tune the conformation of an enzyme (XO) with biocompatible amphiphilic microstructures, which will help to unfold further understanding in the treatment modes of various diseases like gout, hyperuricemia, liver and brain necrosis.

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.

Protonation favors aggregation of lysozyme with SDS

Different proteins have different amino acid sequences as well as conformations, and therefore different propensities to aggregate. Electrostatic interactions have an important role in the aggregation of proteins as revealed by our previous report (J. M. Khan et al., PLoS One, 2012, 7, e29694). In this study, we designed and executed experiments to gain knowledge of the role of charge variations on proteins during the events of protein aggregation with lysozyme as a model protein. To impart positive and negative charges to proteins, we incubated lysozyme at different pH values of below and above the pI (∼11). Negatively charged SDS was used to 'antagonize' positive charges on lysozyme. We examined the effects of pH variations on SDS-induced amyloid fibril formation by lysozyme using methods such as far-UV circular dichroism, Rayleigh scattering, turbidity measurements, dye binding assays and dynamic light scattering. We found that sub-micellar concentrations of SDS (0.1 to 0.6 mM) induced amyloid fibril formation by lysozyme in the pH range of 10.0-1.0 and maximum aggregation was observed at pH 1.0. The morphology of aggregates was fibrillar in structure, as visualized by transmission electron microscopy. Isothermal titration calorimetry studies demonstrated that fibril formation is exothermic. To the best of our current understanding of the mechanism of aggregation, this study demonstrates the crucial role of electrostatic interactions during amyloid fibril formation. The model proposed here will help in designing molecules that can prevent or reverse the amyloid fibril formation or the aggregation.

Effect of luteolin on xanthine oxidase: inhibition kinetics and interaction mechanism merging with docking simulation

Xanthine oxidase (XO) catalyses hypoxanthine and xanthine to uric acid in human metabolism. Overproduction of uric acid will lead to hyperuricemia and finally cause gout and other diseases. Luteolin is one of the major components of celery and green peppers, its inhibitory activity on XO and their interaction mechanism were evaluated by multispectroscopic methods, coupled with molecular simulation. It was found that luteolin reversibly inhibited XO in a competitive manner with inhibition constant (Ki) value of (2.38±0.05)×10(-6) mol l(-1). Luteolin could bind to XO at a single binding site and the binding was driven mainly by hydrophobic interactions. Analysis of synchronous fluorescence and circular dichroism spectra demonstrated that the microenvironment and secondary structure of XO were altered upon interaction with luteolin. The molecular docking results revealed luteolin actually interacted with the primary amino acid residues located within the active site pocket of XO.