A Comparative Study of the Direct Calorimetric Determination of the Denaturation Enthalpy for Lysozyme in Sodium Dodecyl Sulfate and Dodecyltrimethylammonium Bromide Solutions

Investigating the biomolecular interactions between model proteins and glycine betaine surfactant with reference to the stabilization of emulsions and antimicrobial properties

Binding effect and interaction of 2-pentadecanoyloxymethyl)trimethylammonium bromide (DMGM-14) with bovine serum albumin (BSA) and hen egg white lysozyme (HEWL) were systematically investigated by the fluorescence spectroscopy, circular dichroism (CD) spectroscopy, isothermal titration calorimetry (ITC), surface tension analysis, and molecular docking studies. The emulsion properties and particle size distribution of surfactant/protein complexes containing sunflower oil were studied using static light scattering and confocal laser scanning microscopy (CLSM). The fluorescence spectroscopy and ITC analysis confirmed the complexes formation of DMGM-14 with BSA and HEWL which was also verified by surface tension measurements. CD results explained the conformational changes in BSA and HEWL upon DMGM-14 complexation. Molecular docking study provides insight into the binding of DMGM-14 into the specific sites of BSA and HEWL. Besides, the studies drew a detailed picture on the emulsification properties of DMGM-14 with BSA and HEWL. In addition, the in vitro experiment revealed a broad antibacterial spectrum of DMGM-14 and DMGM-14/HEWL complex including activity against Gram-positive and Gram-negative bacteria. In conclusion, the present study revealed that the interaction between DMGM-14 with BSA and HEWL is important for the pharmaceutical, biological, and food products.

Synergistic effect of hen egg white lysozyme and lysosomotropic surfactants on cell viability and membrane permeability

The interactions between two types of quaternary ammonium surfactants (N,N,N-trimethyl-2-(dodecanoyloxy)ethaneammonium bromide (DMM-11) and N,N,N-trimethyl-2-(dodecanoyloxy)propaneammonium bromide (DMPM-11)) and hen egg white lysozyme were studied through several techniques, including isothermal titration calorimetry (ITC), circular dichroism (CD) and fluorescence spectroscopy, and surface tension measurement. The average number of surfactants interacting with each molecule of lysozyme was calculated from the biophysical results. Moreover, the CD results showed that the conformation of lysozyme changed in the presence of DMM-11 and DMPM-11. The studies drew a detailed picture on the physicochemical nature of interactions between both surfactants and lysozyme. Both DMM-11 and DMPM-11, with and without lysozyme were studied against three target microorganisms, including Gram-negative (Escherichia coli) and Gram-positive (Enterococcus hirae and Enterococcus faecalis) bacteria. The results revealed a broad spectrum of antibacterial nature of surfactant/lysozyme complexes, as well as their effect on the membrane damage, hence providing the basis to further explore DMM-11 and DMPM-11 combined with lysozyme as possible antibacterial tools.

Protein extraction into the bicontinuous microemulsion phase of a Water/SDS/pentanol/dodecane winsor-III system: Effect on nanostructure and protein conformation

Bicontinuous microemulsions (BμEs), consisting of water and oil nanodomains separated by surfactant monolayers of near-zero curvature, are potentially valuable systems for purification and delivery of biomolecules, for hosting multiphasic biochemical reactions, and as templating media for preparing nanomaterials. We formed Winsor-III systems by mixing aqueous protein and sodium dodecyl sulfate (SDS) solutions with dodecane and 1-pentanol (cosurfactant) to efficiently extract proteins into the middle (BμE) phase. Bovine serum albumin (BSA) and cytochrome c partitioned to the BμE phase at 64% and 81% efficiency, respectively, producing highly concentrated protein solutions (32 and 44gL^-1, respectively), through release of water and oil from the BμEs. Circular dichroism spectroscopic analysis demonstrated that BSA underwent minor secondary structural changes upon incorporation into BμEs, while the secondary structure of cytochrome c and pepsin underwent major changes. Small-angle x-ray scattering (SAXS) results show that proteins promoted an increase of the interfacial fluidity and surface area per volume for the BμE surfactant monolayers, and that each protein uniquely altered self-assembly in the Winsor-III systems. Cytochrome c partitioned via electrostatic attractions between SDS and the protein's positively-charged groups, residing near the surfactant head groups of BμE monolayers, where it decreased surfactant packing efficiency. BSA partitioned through formation of SDS-BSA complexes via hydrophobic and electrostatic attractive interactions. As the BSA-SDS ratio increased, complexes' partitioning favored BμEs over the oil excess phase due to the increased hydrophilicity of the complexes. This study demonstrates the potential utility of BμEs to purify proteins and prepare nanostructured fluids possessing high protein concentration.

Binding Free Energy and the structural changes determination in hGH protein with different concentrations of copper ions (A molecular dynamics simulation study)

In this study, we estimated the optimum concentration of copper ions that are effective in the stability and the structural changes of human growth hormone (hGH) protein in the combination of different concentrations of these ions at the molecular level using molecular dynamics simulation by Gromacs 4.6.5 software. Moreover, to estimate the binding affinity of copper ions to hGH protein, binding free energies is calculated by the molecular mechanics Poisson–Boltzmann Surface Area (MM-PBSA). The analysis of molecular dynamics (MD) trajectories as dictionary of the secondary structure of protein (DSSP), solvent accessible surface area (SASA) and binding free energy calculations show that hGH protein structure is more stabilized by increasing a limited concentration of copper ions. These findings align with our previous experimental studies.

Surfactants modify the torsion properties of proteins: a single molecule study

Surfactants are widely used in diagnostic assays to prevent protein aggregation and non-specific adsorption at surfaces. Here, a single molecule magnetic torque tweezers study is reported, aiming to quantify surfactant-induced changes in the torsional flexibility of a protein model system: protein-G-immunoglobulin G (IgG) attached to a glass surface. The influences of Sodium Dodecyl Sulphate (SDS) and Polysorbate 20 (Tween 20) on the protein pair have been investigated. The proteins were exposed to the surfactants at concentrations relative to the Critical Micelle Concentration (CMC), namely 0.1× CMC, 1× CMC and 10× CMC. Both surfactants increase the torsional flexibility of the protein-G-IgG complex. Tween 20 is most effective at increasing the torsional flexibility of the complex at the surface while SDS is more effective at dissociating the protein bonds. Tweezer data on the IgG-IgG protein pair show no influence of Tween 20 on the torsional flexibility. Furthermore, temperature dependent near-UV and far-UV Circular Dichroism (CD) data at 10× CMC show that Tween 20 does not significantly alter the secondary and tertiary structure of both protein-G and IgG while SDS does. These results provide evidence that both the mechanical properties of the protein structure and the interaction between proteins can alter the torsional rigidity measured with magnetic torque tweezers. This study shows for the first time the ability to use magnetic torque tweezers as a probe for surfactant-induced changes in proteins at a single molecule level.

Investigation of the Effects of Various Cyclodextrins on the Stabilisation of Human Serum Albumin by a Spectroscopic Method

The binding parameters between cyclodextrins (CDs) and human serum albumin (HSA) were investigated by isothermal titration calorimetry (ITC), fluorescence quenching, and UV-vis absorption spectroscopy at 300 K in 50 mM phosphate buffer solution. Among the various CDs investigated, β-CD has the greater ability to decrease the aggregation of HSA and the results indicated that the inhibition order is γ-CD < α-CD < β-CD. The obtained heats for HSA+CDs interactions were reported and analysed in terms of the extended solvation model, which was used to reproduce the enthalpies of HSA interactions with CDs over a broad range of complex concentrations. The binding constant and thermodynamic parameters were obtained. These suggested that the binding reaction was driven by both enthalpy and entropy, and electrostatic interactions played a major role in the stabilising of HSA. The parameters and reflected the net effect of β-CD on the HSA stability at low and high cyclodextrin concentrations, respectively. The positive values for indicated that β-CD stabilises the HSA structure at low concentrations. The UV absorption intensity of theses complexes increased and a slight red shift was observed in the absorbance wavelength with increasing the CD concentration. The fluorescence intensity of HSA decreased regularly and a slight blue shift was observed for the emission wavelength with increasing CD concentration. The results indicate that the CD complex could quench the fluorescence of HSA and changes the microenvironment of the tryptophan residue.

Thermal Study of a Newly Synthesized Cu(II) Complex Binding to Bovineβ-Lactoglobulin

We have investigated the interactions betweenβ-lactoglobulin, BLG, and new synthesized Cu(II) complex (2,2′-dibipyridine Cu(II) chloride) using isothermal titration calorimetry (ITC) methods at different temperatures of 298 and 310 K. The heats of BLG + Cu(II) interactions are reported and analyzed in terms of the extended solvation theory for calculation of binding and thermodynamic parameters of the interaction. The results suggested that binding of Cu(II) complex on BLG resulted in significant changes on the tertiary structure and conformation of protein via increasing of hydrophobicity and inducing partially unfolded structure in BLG which has a good agreement with the solvation parameters recovered by the extended solvation model suggesting destabilization of the protein.

Thermodynamic Study of Human Serum Albumin upon Interaction with Ytterbium (III)

Complexation reaction between Yb3+and human serum albumin is examined using isothermal titration calorimetry (ITC). The extension solvation theory was used to reproduce the enthalpies of HAS + Yb3+interactions over the whole range of Yb3+concentrations. The binding parameters recovered from this model were attributed to the structural change of HSA. The results show that Yb3+ions bind to HSA with three equivalent affinity sites. It was found that in the high concentrations of the ytterbium ions, the HSA structure was destabilized.

A Comparative Interaction between Copper Ions with Alzheimer's β Amyloid Peptide and Human Serum Albumin

The interaction of Cu(2+) with the first 16 residues of the Alzheimer's amyliod β peptide, Aβ(1-16), and human serum albumin (HSA) were studied in vitro by isothermal titration calorimetry at pH 7.2 and 310 K in aqueous solution. The solvation parameters recovered from the extended solvation model indicate that HSA is involved in the transport of copper ion. Complexes between Aβ(1-16) and copper ions have been proposed to be an aberrant interaction in the development of Alzheimer's disease, where Cu(2+) is involved in Aβ(1-16) aggregation. The indexes of stability indicate that HSA removed Cu(2+) from Aβ(1-16), rapidly, decreased Cu-induced aggregation of Aβ(1-16), and reduced the toxicity of Aβ(1-16) + Cu(2+) significantly.

Thermodynamic study of the binding of calcium and magnesium ions with myelin basic protein using the extended solvation theory

The interaction of myelin basic protein (MBP) from the bovine central nervous system with Ca2+ and Mg2+ ions, named as M2+, was studied by isothermal titration calorimetry at 27 degrees C in aqueous solution. The extended solvation model was used to reproduce the enthalpies of MBP+M2+ interactions. The solvation parameters recovered from the extended solvation model were attributed to the structural change of MBP due to the metal ion interaction. It was found that there is a set of two identical and noninteracting binding sites for Ca2+ and Mg2+ ions.