Physicochemical study of the interaction of lysozyme with surface active ionic liquid 1-butyl-3-methylimidazolium octylsulfate [BMIM] [OS] in aqueous and buffer media

Addressing the interaction of stem bromelain with different anionic surfactants, below, at and above the critical micelle concentration (cmc) in phosphate buffer at pH 7: Physicochemical, spectroscopic, & molecular docking study

The structural stability and therapeutic activity of Stem Bromelain (BM) have been explored by unravelling the interaction of stem BM in presence of two different types of anionic surfactants namely, bile salts, NaC and NaDC and the conventional anionic surfactants, SDDS and SDBS, below, at and above the critical micelle concentration (cmc) in aqueous phosphate buffer of pH 7. Different physicochemical parameters like, surface excess (Γcmc), minimum area of surfactants at air water interface (Amin) etc. are calculated from tensiometry both in absence and presence of BM. Several inflection points (C1, C2 and C3) have been found in tensiometry profile of surfactants in presence of BM due to the conformational change of BM assisted by surfactants. Similar observation also found in isothermal titration calorimetry (ITC) profiles where the enthalpy of micellization (ΔH0obs) of surfactants in absence and presence of BM have calculated. Further, steady state absorption and fluorescence spectra monitoring the tryptophan (Trp) emission of free BM and in presence of all the surfactants at three different temperatures (288.15 K, 298.15 K, and 308.15 K) reveal the nature of fluorescence quenching of BM in presence of bile salts/surfactants. Time resolved fluorescence studies at room temperature also support to determine the several quenching parameters. The binding constant (Kb) of BM with all the surfactants and free energy of binding (∆G0 of bile salts/surfactants with BM at different temperatures have been calculated exploiting steady state fluorescence technique. It is observed that, the binding of NaC with BM is greater as compared to other surfactants while Stern-Volmer quenching constant (KSV) is found greater in presence of SDBS as compared with others which supports the surface tension and ITC data with the fact that surface activity of surfactant(s) is decreasing with the binding of the surfactants at the core or binding pocket of BM. Circular Dichroism (CD) study shows the stability of secondary structure of BM in presence of NaC and NaDC below C3, while BM lost its structural stability even at very low surfactant concentration of SDDS and SDBS which also supports the more involvement of bile salts in binding rather than surfactants. The molecular docking studies have also been substantiated for better understanding the several experimental investigations interaction of BM with the bile salts/surfactants.

Towards Enhanced Tunability of Aqueous Biphasic Systems: Furthering the Grasp of Fluorinated Ionic Liquids in the Purification of Proteins

This work unfolds functionalized ABSs composed of FILs ([C2C1Im][C4F9SO3] and [N1112(OH)][C4F9SO3]), mere fluoro-containing ILs ([C2C1Im][CF3SO3] and [C4C1Im][CF3SO3]), known globular protein stabilizers (sucrose and [N1112(OH)][C4F9SO3]), low-molecular-weight carbohydrate (glucose), and even high-charge density salt (K3PO4). The ternary phase diagrams were determined, stressing that FILs highly increased the ability for ABS formation. The functionalized ABSs (FILs vs. mere fluoro-containing ILs) were used to extract lysozyme (Lys). The ABSs' biphasic regions were screened in terms of protein biocompatibility, analyzing the impact of ABS phase-forming components in Lys by UV-VIS spectrophotometry, CD spectroscopy, fluorescence spectroscopy, DSC, and enzyme assay. Lys partition behavior was characterized in terms of extraction efficiency (% EE). The structure, stability, and function of Lys were maintained or improved throughout the extraction step, as evaluated by CD spectroscopy, DSC, enzyme assay, and SDS-PAGE. Overall, FIL-based ABSs are more versatile and amenable to being tuned by the adequate choice of the phase-forming components and selecting the enriched phase. Binding studies between Lys and ABS phase-forming components were attained by MST, demonstrating the strong interaction between Lys and FILs aggregates. Two of the FIL-based ABSs (30 %wt [C2C1Im][C4F9SO3] + 2 %wt K3PO4 and 30 %wt [C2C1Im][C4F9SO3] + 25 %wt sucrose) allowed the simultaneous purification of Lys and BSA in a single ABS extraction step with high yield (extraction efficiency up to 100%) for both proteins. The purity of both recovered proteins was validated by SDS-PAGE analysis. Even with a high-charge density salt, the FIL-based ABSs developed in this work seem more amenable to be tuned. Lys and BSA were purified through selective partition to opposite phases in a single FIL-based ABS extraction step. FIL-based ABSs are proposed as an improved extraction step for proteins, based on their biocompatibility, customizable properties, and selectivity.

Alcohol-Induced Denaturation of Hen Egg White Lysozyme Studied by Infrared, Circular Dichroism, and Small-Angle Neutron Scattering

In aqueous binary solvents with fluorinated alcohols, 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and aliphatic alcohols, ethanol (EtOH) and 2-propanol (2-PrOH), the denaturation of hen egg white lysozyme (HEWL) with increasing alcohol mole fraction xA has been investigated in a wide view from the molecular vibration to the secondary and ternary structures. Circular dichroism (CD) measurement showed that the secondary structure of α-helix content of HEWL increases on adding a small amount of the fluorinated alcohol to the aqueous solution, while the β-sheet content decreases. On the contrary, the secondary structure does not significantly change by the addition of the aliphatic alcohols. Correspondingly, the infrared (IR) spectroscopic measurements revealed that the amide I band red-shifts on the addition of the fluorinated alcohol. However, the band remains unchanged in the aliphatic alcohol systems with increasing alcohol content. To observe the ternary structure of HEWL, small-angle neutron scattering (SANS) experiments with H/D substitution technique have been applied to the HEWL solutions. The SANS experiments were successful in revealing the details of how the geometry of the HEWL changes as a function of xA. The SANS profiles indicated the spherical structure of HEWL in all of the alcohol systems in the xA range examined. The mean radius of HEWL in the two fluorinated alcohol systems increases from ∼16 to ∼18 Å during the change in the secondary structure against the increase in the fluorinated alcohol content. On contrast, the radius does not significantly change in both aliphatic alcohol systems below xA = 0.3 but expands to ∼19 Å as the alcohol content is close to the limitation of the HEWL solubility. According to the present results, together with our knowledge of the alcohol cluster formation and the interaction of the trifluoromethyl (CF3) groups with the hydrophobic moieties of biomolecules, the effects of alcohols on the denaturation of the protein have been discussed on a molecular scale.

Do Ionic Liquids Exhibit the Required Characteristics to Dissolve, Extract, Stabilize, and Purify Proteins? Past-Present-Future Assessment

Proteins are highly labile molecules, thus requiring the presence of appropriate solvents and excipients in their liquid milieu to keep their stability and biological activity. In this field, ionic liquids (ILs) have gained momentum in the past years, with a relevant number of works reporting their successful use to dissolve, stabilize, extract, and purify proteins. Different approaches in protein-IL systems have been reported, namely, proteins dissolved in (i) neat ILs, (ii) ILs as co-solvents, (iii) ILs as adjuvants, (iv) ILs as surfactants, (v) ILs as phase-forming components of aqueous biphasic systems, and (vi) IL-polymer-protein/peptide conjugates. Herein, we critically analyze the works published to date and provide a comprehensive understanding of the IL-protein interactions affecting the stability, conformational alteration, unfolding, misfolding, and refolding of proteins while providing directions for future studies in view of imminent applications. Overall, it has been found that the stability or purification of proteins by ILs is bispecific and depends on the structure of both the IL and the protein. The most promising IL-protein systems are identified, which is valuable when foreseeing market applications of ILs, e.g., in "protein packaging" and "detergent applications". Future directions and other possibilities of IL-protein systems in light-harvesting and biotechnology/biomedical applications are discussed.

Comprehensive NMR Investigation of Imidazolium-Based Ionic Liquids [BMIM][OSU] and [BMIM][Cl] Impact on Binding and Dynamics of the Anticancer Drug Doxorubicin Hydrochloride

For the design of an efficient drug delivery system utilizing an ionic liquid (IL) as a carrier, it is prudent to gain molecular/atomistic level insights of a drug with IL in terms of binding and dynamics. In this scenario, the influence of anionic counterpart of imidazolium-based ILs, namely, 1-butyl-3-methyl-imidazolium octyl sulfate [BMIM][OSU] and 1-butyl-3-methyl-imidazolium chloride [BMIM][Cl] in their submicellar region ([IL] = 20 mM) on the model water-soluble anticancer drug doxorubicin hydrochloride (DOX) was probed by employing an arsenal of nuclear magnetic resonance (NMR) approaches. The salient feature of the present study includes the significant interaction of DOX with [BMIM][OSU], whereas the lack of such an interaction with [BMIM][Cl] is gauged by 1H NMR translation self-diffusometry and is further corroborated by 13C chemical shift perturbation. The two-step model was utilized to estimate the bound fraction (pb) and equivalent partition coefficient (K) of DOX with [BMIM][OSU]. A combination of selective and nonselective spin-lattice relaxation rates (R1SEL and R1NS, respectively) enables to gauze the significant interaction of DOX with [BMIM][OSU] over [BMIM][Cl]. Furthermore, 1D transient and truncated driven nuclear Overhauser enhancement (NOE) data analyses in the initial rate limit permits the evaluation of the cross-relaxation efficacy of DOX with the investigated ILs. An Arrhenius-type temperature dependence of the drug's self-diffusion was observed for DOX, DOX-[BMIM][OSU], and DOX-[BMIM][Cl] aqueous mixtures and the corresponding activation energies were evaluated.

pH-Induced Biophysical Perspectives of Binding of Surface-Active Ionic Liquid [BMIM][OSU] with HSA and Dynamics of the Formed Complex

The influence of pH on the human serum albumin (HSA) interaction with ionic liquid (IL)1-butyl 3-methylimidazolium octyl sulfate ([BMIM][OSU]) at its sub-micellar concentration of 5 mM (well below CMC ∼31 mM at 25 °C) in aqueous solution has been monitored employing different methods, viz., circular dichroism (CD), fluorescence, electrokinetic determination of the zeta potential (ZP), nuclear magnetic resonance (NMR), small-angle neutron scattering (SANS), and molecular docking (MD). CD analysis indicated a noticeable reduction of the α-helical content of HSA by IL at pH 3. A significant interaction of the anionic part of IL with HSA was evident from the ¹H chemical shifts and saturation transfer difference (STD) NMR. A strong binding between IL and HSA was observed at pH 3 relative to pH 5, revealing the importance of electrostatic and hydrophobic interactions assessed from global binding affinities and molecular correlation times derived from STD NMR and a combined selective/nonselective spin-relaxation analysis, respectively. ZP data supported the electrostatic interaction between HSA and the anionic part of IL. The nature of IL self-diffusion with HSA was assessed from the translational self-diffusion coefficients by pulse field gradient NMR. SANS results revealed the formation of prolate ellipsoidal geometry of the IL-HSA complex. MD identified the preferential binding sites of IL to the tryptophan centers on HSA. The association of IL with HSA was supported by fluorescence measurements, in addition to the structural changes that occurred in the protein by the interaction with IL. The anionic part of IL contributed a major interaction with HSA at the pH levels of study (3, 5, 8, and 11.4); at pH > 8 (effectively 11.4), the protein also interacted weakly with the cationic component of IL.

An Overview of Coacervates: The Special Disperse State of Amphiphilic and Polymeric Materials in Solution

Individual amphiphiles, polymers, and colloidal dispersions influenced by temperature, pH, and environmental conditions or interactions between their oppositely charged pairs in solvent medium often produce solvent-rich and solvent-poor phases in the system. The solvent-poor denser phase found either on the top or the bottom of the system is called coacervate. Coacervates have immense applications in various technological fields. This review comprises a concise introduction, focusing on the types of coacervates, and the influence of different factors in their formation, structures, and stability. In addition, their physicochemical properties, thermodynamics of formation, and uses and multifarious applications are also concisely presented and discussed.

The Effect of Luteolin and Luteoloside on the Secondary Structure of Lysozyme

The changes of lysozyme conformation in the absence and presence of luteolin and luteoloside were investigated by spectral analysis including fluorescence, UV, CD, Raman, and ATR-FTIR, and the biological activity of lysozyme was investigated by lysozyme assay kit. The results showed that the microenvironment hydrophobicity of lysozyme increased and peptide extension decreased with the addition of luteolin or luteoloside. The α-helix of lysozyme might be influenced by luteolin or luteoloside, and its relative content had a significant difference after adding luteolin or luteoloside by the ATR-FTIR method, which was reconfirmed by CD and Raman spectra. The lysozyme activity changed obviously after adding luteolin or luteoloside. All of the conclusions above indicated the active site of lysozyme in the α-helix might be influenced by luteolin and luteoloside.

Use of Ionic Liquids in Protein and DNA Chemistry

Ionic liquids (ILs) have been receiving much attention as solvents in various areas of biochemistry because of their various beneficial properties over the volatile solvents and ILs availability in myriad variants (perhaps as many as 108) owing to the possibility of paring one cation with several anions and vice-versa as well as formulations as zwitterions. Their potential as solvents lies in their tendency to offer both directional and non-directional forces toward a solute molecule. Because of these forces, ionic liquids easily undergo intermolecular interactions with a range of polar/non-polar solutes, including biomolecules such as proteins and DNA. The interaction of genomic species in aqueous/non-aqueous states assists in unraveling their structure and functioning, which have implications in various biomedical applications. The charge density of ionic liquids renders them hydrophilic and hydrophobic, which retain intact over long-range of temperatures. Their ability in stabilizing or destabilizing the 3D-structure of a protein or the double-helical structure of DNA has been assessed superior to the water and volatile organic solvents. The aptitude of an ion in influencing the structure and stability of a native protein depends on their ranking in the Hofmeister series. However, at several instances, a reverse Hofmeister ordering of ions and specific ion-solute interaction has been observed. The capability of an ionic liquid in terms of the tendency to promote the coiling/uncoiling of DNA structure is noted to rely on the basicity, electrostatic interaction, and hydrophobicity of the ionic liquid in question. Any change in the DNA's double-helical structure reflects a change in its melting temperature (T m), compared to a standard buffer solution. These changes in DNA structure have implications in biosensor design and targeted drug-delivery in biomedical applications. In the current review, we have attempted to highlight various aspects of ionic liquids that influence the structure and properties of proteins and DNA. In short, the review will address the issues related to the origin and strength of intermolecular interactions, the effect of structural components, their nature, and the influence of temperature, pH, and additives on them.

NMR investigations on binding and dynamics of imidazolium-based ionic liquids with HEWL

Molecular level insights on protein-ionic liquid (P-IL) interactions are beneficial for assessing protein stability, binding and dynamics. In the present work, interactions of ILs, namely, 1-butyl 3-methylimidazolium methyl sulfate (IL1), 1-butyl 3-methylimidazolium octyl sulfate (IL2) and 1-butyl 3-methylimidazolium chloride (IL3) with hen egg white lysozyme (HEWL) protein were investigated using solution-state nuclear magnetic resonance (NMR) spectroscopy. To ascertain the binding and dynamics from the perspective of both protein and IL, various ligand based NMR approaches such as selective and non-selective nuclear spin-relaxation (R_1SEL and R_1NS), saturation transfer difference (STD), difference of inversion recovery rate with and without target irradiation (DIRECTION), ³⁵Cl line-shape and spin-relaxation, and protein back bone amide chemical shift perturbations (CSPs) from ¹H-¹⁵N HSQC were utilized. Among the ILs investigated, IL2 experiences significant interaction relative to those of IL1 and IL3, as revealed by the combined R_1SEL and R_1NS analysis, which is further supported by STD NMR. CSP analyses of ¹H-¹⁵N HSQC spectra of aqueous P-IL mixtures enabled to identify the potential binding sites of ILs with HEWL. Whereas, ¹⁵N longitudinal (R₁) and transverse (R₂) spin-relaxation rates and ¹⁵N{¹H} heteronuclear nuclear Overhauser effect (hetNOE) data subjected to the model free analysis for IL2 yielded the rotational correlation times and order parameters of various residues of HEWL. Furthermore, the results could discern the nature of interactions between studied ILs and HEWL in terms of specific and non-specific interactions.

Structural-functional integrity of lysozyme in imidazolium based surface active ionic liquids

The present study was designed to explore the hydrophobicity and concentration dependence of imidazolium based surface active ionic liquids (SAILs) effects on the structural-functional integrity of proteins. Specifically, we investigated the impact of SAILs viz. 1-octyl-3-methylimidazolium dodecylbenzenesulfonate ([OMIM][DBS]) and 1-dodecyl-3-methylimidazolium dodecylbenzenesulfonate ([DDMIM][DBS]) on activity, structure and stability of lysozyme. Activity measurements revealed that, in contrast to [DDMIM][DBS] that renders lysozyme either feebly active or inactive, [OMIM][DBS] significantly enhances the lysozyme activity in the concentration range of critical aggregation concentrations (CAC) to C_s (SAIL saturation concentration of protein backbone) i.e., 0.5 mM-1.35 mM. Tensiometric results in agreement with turbidity measurements inferred significant composition and concentration dependence of the lysozyme-SAIL interactions. Spectroscopic investigations revealed that compared to destabilizing behaviour of [DDMIM][DBS], [OMIM][DBS] significantly enhances both conformational as well as thermal stability of lysozyme in the CAC to C_s concentration regime. Altogether, results obtained do indicate that [OMIM][DBS], in the concentration regime of CAC to C_s, serves as an efficient stabiliser with an ability to appreciably enhance the activity, thermal stability and overall conformational stability of lysozyme. We firmly believe that [OMIM][DBS], at least in the CAC to C_s concentration ranges, can be exploited as a promising stabiliser and activity enhancer for numerous industrially important enzymes.

Modulations in Self-Organization Properties of Surfactant in Aqueous Ionic Liquid Media

Ionic liquids (ILs) give a wide scope of favorable applications due to their much-upgraded properties. The strong electrostatic interactions between the cationic moiety of IL and the anionic surfactant play a very important role in the assembly of the large aggregates. We have investigated the aggregation behavior of anionic surfactants and IL in aqueous solution. Different temperatures and concentrations of IL have been taken to study the effect on critical micelles concentrations of surfactant. The critical micelle concentration values obtained by conductivity measurements are further confirmed by the fluorescence studies. The method is based on the fit of the experimental obtained raw data of fluorescence spectroscopy to a simple nonlinear category of a Boltzmann type sigmoidal function. Thermodynamical parameters of micellization Δ H m 0 $\Delta H_{m}^{0}$ , Δ G m 0 $\Delta G_{m}^{0}$ and Δ S m 0 $\Delta S_{m}^{0}$ have been considered to study the effect of aqueous IL 1-butyl-3-methylimidazolium bromide concentration and temperature on aggregation behavior of surfactant sodium dodecyl sulfate. FT-IR spectra have been studies to verify the structural changes arise in the aqueous IL and surfactant system.

The antimicrobial spectrum of lysozyme broadened by reductive modification

In order to broaden the antimicrobial action spectrum of lysozyme against Gram-negative bacteria, different partially reduced lysozyme derivatives were obtained by reducing the R-S-S-R bonds of lysozyme using the reducing agent Na2SO3. The circular dichroism behavior analysis showed that the tertiary structure of the partially reduced lysozyme molecules became more flexible, leading to an obvious increase in the surface hydrophobicity and the tryptophan fluorescence intensity. Zeta potential analysis indicated that the introduction of SO32- led to a decrease in the surface charges of the reduced lysozyme molecules. Compared with the native lysozyme, the reduced lysozymes not only showed a 1 log increase in the antimicrobial activity against Escherichia coli ATCC 25922 and Salmonella enteritidis ATCC 13076 (P <0.05), but also maintained nearly the same antimicrobial activity against Staphylococcus aureus ATCC 29213 (P >0.05). Overall, the reductive modification with the food-friendly, compatible, and safe reducing agent Na2SO3 has broadened the antimicrobial action spectrum of the modified lysozymes against Gram-negative bacteria, with the enhancement extent depending on the reduction degree and the type of bacterial strains. The integrated results suggest that the Na2SO3-reduced lysozyme can be used as a novel safe potential bactericidal additive for food-processing industry.

Comparative effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and activity of lysozyme

Protein interactions with surfactants are dependent on their physiochemical properties.

Comparative effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and activity of lysozyme

Protein interactions with surfactants are dependent on their physiochemical properties.

Comparative effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and activity of lysozyme

Protein interactions with surfactants are dependent on their physiochemical properties.

Comparative effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and activity of lysozyme

Protein interactions with surfactants are dependent on their physiochemical properties.

Comparative effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and activity of lysozyme

Protein interactions with surfactants are dependent on their physiochemical properties.

Detailed characterization of lysozyme (Lyz)–surfactant (SDDS) interaction and the structural transitions

Surfactant interaction can influence the protein structure manifesting molecular unfolding–folding.