Conformation and interactions of uteroglobin fragments 4–14 and 49–65 in aqueous solution containing surfactant micelles

The conformation of two fragments of rabbit uteroglobin is described. The peptides are PRFAHVIENLL and PQTTRENIMKLTEKIVK, corresponding to helices I and IV in the crystal structure. CD shows that both peptides interact with sodium dodecyl sulfate (SDS) micelles and change their conformation to an α-helix. The helical content estimated from the CD band at 222 nm is about 40% in each peptide. Surface tension measurements show that both peptides lower the critical micellar concentration (cmc) of SDS, with a more dramatic effect in the case of helix I. This peptide by itself acts as a surfactant, and is able to interact with SDS even below the observed cmc, forming β aggregates. Proton magnetic resonance (¹H-nmr) suggests that flexible helices are present. The longest helical stretches compatible with ¹H-nmr data extend from Phe⁶ to Leu¹⁴ for helix I and from Arg⁵³ to Ile⁶³ for helix IV. © 1993 John Wiley & Sons, Inc.     

Conformational studies by circular dichroism, 1H NMR, and computer simulations of bombolitins I and III in aqueous solution containing surfactant micelles

The heptadecapeptides bombolitin I and bombolitin III are two members of a series of biologically active peptides postulated to be membrane active. In order to understand the effects of the membrane on the secondary structure of the peptides, we have carried out the conformational characterization of bombolitins I and III in the presence of SDS micelles using circular dichroism, nuclear magnetic resonance, and computer simulations. The characteristic bands in the circular dichroism spectra indicate an alpha-helix content of approximately 60% in bombolitin III and 70% in bombolitin I. The observation of NOE's quite distinctive for such secondary structure strongly supports the CD results. The conformational preferences of the two bombolitins derived from CD and NMR were then energetically refined with molecular dynamics simulations. The results from the spectroscopic examination were utilized as input for the simulations, the CD results for generation of the initial structure, and the NOE's as constraints during the simulations. The results from the different techniques employed are in complete agreement.     

Conformation of allantoicase in aqueous solution

1. The separation of 0.9-S and 10.8-S allantoicase with the aid of a 2H2O-H2O gradient was described. The resulting preparations were subjected to sedimentation equilibrium, optical rotatory dispersion (ORD), circular dichroism (CD) and infrared studies. 2. The molecular weight of 0.9-S allantoicase was determined to be about 1.1 x 10(4) g/mole in studies on the sedimentation behavior, the metal content and amino acid composition. The molecular weight of 10.8-S allantoicase was about 15.4 x 10(4) g/mole. 3. Optical rotatory dispersion, circular dichroism and infrared studies indicated that both molecules contain alpha-helix, beta conformation and random coil. A Cotton effect at 418 nm was ascribed to the asymmetric binding of Mn2+ to the enzyme. Competitive inhibitors decreased the absorption and circular dichroism bands at about 280 nm and 418 nm. These phenomena suggested that the aromatic groups may play an essential role in the binding of substrates and inhibitors by the Mn(2+)-enzyme complex. 4. Comparison of alpha-helical contents of metalloallantoicases showed that the enzymes with low helical contents exhibited high enzymic activities. 5. The nearly identical physicochemical behavior and specific enzymic activity of 0.9-S and 10.8-S allantoicase indicated that they are very similar in structure and conformation.     

Conformation of poly-L-tyrosine in aqueous solution

The conformational transition of poly-L -tyrosine in 0.1M KCl was investigated by ORD and infrared spectroscopy, potentiometric titration, and sedimentation velocity experiments. It is shown that the fully ordered conformer is obtained by slow titration of the random coil with 0.1N HCl at 25°C. The charge-induced transition, at variance with other poly-α-amino acids, is completed in a narrow range of α. An aggregation process was detected both by potentiometric titration and sedimentation velocity. The polyamino acid aggregates around α = 0.7 at 25°C when the conformational transition is almost complete. Infrared spectra, in the region of the amide I band (1650 cm^?1) showed that the transition is a random coil → antiparallel β one. Evidence exists that the form is of the intramolecular type. The foregoing interpretations of ORD and CD spectra in terms of the α-helix conformation are discussed.     

Conformation of Vespa basalis mastoparan-B in trifluoroethanol-containing aqueous solution

Mastoparan-B, a tetradecapeptide isolated from the venom of the hornet Vespa basalis, belongs to the mastoparan analogs of vespid venom with the lysine residues common for all mastoparan family toxins at positions 4, 11 and 12. Here we use ¹H-NMR spectroscopy and hybrid distance geometry-simulated annealing calculation to investigate its three-dimensional structure in trifluoroethanol-containing aqueous solution. The calculated structure shows that residues 3–14 adopt an amphiphilic α-helical structure in which the residues with hydrophilic side chains (i.e. Lys-4, Ser-5, Ser-8, Lys-11, Lys-12) are located on one side and the residues with hydrophobic side chains (i.e. Leu-3, Ile-6, Trp-9, A a-10, Val-13, Leu-14) located on the other side of the molecule. The overall structural features are very similar to the conformation of mastoparan-X reconstituted in vesicles [Wakamatsu et al. (1992) Biochemistry 31, 5654–5660] in spite of the substitutions made for eight residues with distinctly different hydrophobicity. These substitutions lead to a larger hydrophobic moment for the α-helical segment and further mobilized N-terminal. This study will help reveal the conformational significance of mastoparan toxins with respect to their potency and activity in G protein regulation.     

Conformation of a T cell stimulating peptide in aqueous solution

Using two-dimensional NMR spectroscopy and circular dichroism spectroscopy it is demonstrated that a T cell stimulating peptide corresponding to residues 132-153 of sperm whale myoglobin populates helical conformations in aqueous solution. This finding is in accordance with proposals that immunodominant sites in T cell stimulating peptides have a high conformational propensity. The observation of secondary structure in aqueous solutions of this and other immunogenic peptides has important implications for initiation of protein folding.     

Enhanced chemiluminescence of lucigenin with epinephrine in cationic surfactant micelles containing periodate

Epinephrine (EP) species involved in the lucigenin chemiluminescence (CL) were identified in alkaline solution by comparing the time course of the CL response and the formation of EP oxidation products. EP quinone and adrenolutine (AL) were found to be responsible for the lucigenin-CL reaction. The mechanism of the lucigenin-CL enhancement was investigated using cationic micellar hexadecyltrimethylammonium hydroxide (CTAOH), periodate, and a mixture of micellar CTAOH and periodate. The CL enhancement in the presence of micellar CTAOH and periodate could be explained in terms of increases in the oxidation rate of EP to EP quinone and the intramolecular oxidation rate of adrenochrome to AL.     

Fluorescence dynamics of staphylococcal nuclease in aqueous solution and reversed micelles

The dynamical fluorescence properties of the sole tryptophan residue (Trp-140) in Staphylococcus aureus nuclease (EC 3.1.31.1) have been investigated in aqueous solution and reversed micelles composed of either sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in isooctane or cetyltrimethylammonium chloride (CTAC) in isooctane/hexanol (12:1 by volume). The fluorescence decay of nuclease in the different environments can be described by a trimodal distribution of fluorescence lifetimes at approx. 0.5, 1.5 and 5.0 ns. The relative amplitudes depend on the environment. For pH 9.0 solutions the contribution of the two shortest lifetime components in the distribution is largest for AOT and smallest for CTAC reversed micelles. There is reasonable agreement between the average fluorescence lifetime and the fluorescence quantum efficiency confirming a significant fluorescence quenching in AOT reversed micelles. Fluorescence anisotropy decay revealed that the tryptophan environment in aqueous nuclease solutions is rigid on a nanosecond timescale. When nuclease was entrapped into reversed micelles the tryptophan gained some internal flexibility as judged from the distinct presence of a shorter correlation time. The longer correlation time reflected the rotational properties of the protein-micellar system. Modulation of the overall charge of nuclease (isoelectric point pH 9.6) by using buffer of pH 9.0 and pH 10.4, respectively, and of the size of empty micelles by selecting two values of the water to surfactant molar ratio, had only a minor effect on the rotational properties of nuclease in the positively charged reversed micelles. Encapsulation of nuclease in anionic reversed micelles resulted in the development of protein bound to aggregated structures which are immobilised on a nanosecond timescale. According to far UV vircular dichroism results the secondary structure of nuclease only followed the already published pH-dependent changes. Encapsulation had no major effect on the overall secondary structure.     

The interaction between vitamin B-12 and micelles in aqueous solution

The apparent pK for benzimidazole displacement of a number of cobalamins is markedly affected by the presence of sodium lauryl sulfate micelles. However, micelles of cetyltrimethylammonium bromide or Triton X have little or no effect on the pK. By measuring the apparent pK as a function of sodium lauryl sulfate concentration, the association constants between the micelles and both base on and base off methylcobalamin were calculated. This calculation indicates that the base off form is strongly associated with the micelle while the base on form is not.     

Conformation of recombinant desulfatohirudin in aqueous solution determined by nuclear magnetic resonance

The three-dimensional structure of recombinant desulfatohirudin in aqueous solution was determined by 1H nuclear magnetic resonance at 600 MHz and distance geometry calculations with the program DISMAN. The input for the structure calculations was prepared on the basis of complete sequence-specific resonance assignments at pH 4.5 and 22 degrees C and consisted of 425 distance constraints from nuclear Overhauser enhancements and 159 supplementary constraints from spin-spin coupling constants and from the identification of intramolecular hydrogen bonds. Residues 3-30 and 37-48 form a molecular core with two antiparallel beta-sheets and several well-defined turns. The three disulfide bonds 6-14, 16-28, and 22-39 were identified by NMR. In contrast to this well-defined molecular core, with an average root mean square distance for the polypeptide backbone of 0.8 A for a group of nine DISMAN solutions, no preferred conformation was found for the C-terminal segment 49-65, and a loop consisting of residues 31-36 is not uniquely constrained by the NMR data either. These structural properties of recombinant desulfatohirudin coincide closely with the previously described solution conformation of natural hirudin, but the presence of localized differences is indicated by chemical shift differences for residues Asp 5, Ser 9, Leu 15, Asp 53, Gly 54, and Asp 55.     

The interaction of calcium ions with glycocholate micelles in aqueous solution.

The formation of soluble complexes of Ca2+ ions and glycocholate has been demonstrated. The dissociation constant is 26 nmol/litre and a maximum of 2 Ca2+ ions are bound to each glycocholate micelle. The formation of this complex is shown to be reversible. Binding is increased by the introduction of phosphatidylcholine into the micelle; it is decreased by a decrease in pH and by increased counter-ion concentration. The biological significance of these effects is discussed.     

Thermotropic phase behavior and stability of monosialoganglioside micelles in aqueous solution.

The thermotropic phase behavior of monosialoganglioside in a dilute aqueous dispersion at pH 6.8 was measured by using synchrotron radiation small-angle x-ray scattering and was analyzed by a shell-modeling method. Previous calorimetric studies on ganglioside systems have shown quite different thermotropic behaviors from other biological lipid systems, however, the details have still been ambiguous. Because of high statistical data and a shell-modeling analysis, we could elucidate the internal structural change of monosialoganglioside micelle induced by the elevation of temperature from 6 to 60 degrees C, that is, the shrinkage of the hydrophilic region and the slight expansion of the hydrophobic region occurring simultaneously, accompanying the elongation of the axial ratios of the ellipsoidal micelles. The model structures obtained explain the changes in the experimental scattering curves, the distance distribution functions, and the gyration radii. In addition we have also found an evident thermal hysteresis in the scattering curves and in the structural parameters. The present result suggests that the thickness of the hydrophilic region, namely, the conformation of oligosaccharide chains, is sensitive to a change of temperature.     

Conformation and reduction-oxidation properties of cytochrome c incorporated into reversed micelles of a surfactant in an organic solvent

Changes observed in CD- and absorption spectra of cytochrome c solubilized in reversed micelles AOT showed significant structural transformations of protein in the region of the active centre and particularly revealed a replacement of the sixth ligand of heme iron. These changes also affected the redox properties of cytochrome c.     

Self-assembly of surfactant aqueous solution confined in a Janus amphiphilic nanotube

Abstract

In recent years, Janus amphiphilic nanotubes with complex surfaces have been synthesized. However, the self-assembly behaviour of surfactant solutions confined in a Janus amphiphilic nanotube has not been investigated so far. We performed molecular simulations to investigate the morphologies and phase diagrams of a surfactant confined in Janus amphiphilic nanotube consisting of both hydrophobic and hydrophilic surfaces. We derived a phase diagram of the representative snapshots of equilibrium morphologies. Morphologies that were not observed in the bulk eventuated in confined systems. Moreover, the self-assembled structures were found to be dependent on the spatial confinement. Furthermore, the self-assembled structures confined in hydroneutral and Janus amphiphilic nanotubes were compared. The results suggested that the self-assembled structures confined in the Janus amphiphilic nanotube resembled that confined in the hydroneutral nanotube owing to a strong confinement effect. Further developments in controlling the morphologies and self-assemblies will greatly advance their applications of these materials in nanofluidic devices, or for nanopatterning.     

Behaviour of scleroglucan in aqueous solution containing sodium hydroxide

This paper reports the behaviour of scleroglucan in aqueous solution as a function of NaOH concentration and temperature. Two different transitions are observed. The first one, reversible when temperature varies, is attributed to a change in the local structure of the side chain glucose residues and water organization in the triple helix conformation. The second one, irreversible, is due to the conformational transition from the triple helix to the coil. It is found that 0.20 and 0.01 m NaOH are good solvents to charaterize the single chain and the triple helical structure respectively. The presence of NaOH, even at the low concentration 0.01 m, modifies the polymer solubility such as to prevent gel formation, which may occur in the absence of added salt due to triple helix interactions at temperature below the temperatures of the first transition.     

Conformation of amylose–iodine–iodide complex in aqueous solution

The conformational characteristics of the amylose–iodine–iodide complex in aqueous solution, particularly for a rapidly mixed system, were studied by resonance polarized scattering measurements using a He-Ne laser at low concentrations of the complex and by viscosity measurements at high concentrations of the complex. For the scattering measurements, the following results were obtained: the depolarization ratios ρ_u and ρ_v showed a pronounced increase with the degree of saturation of the bound iodine (q) in amylose, depending on KI concentration. At q ? 0.7, the increase in these values appeared to be suppressed. However, the ρ_h value was approximately 1, irrespective of q. Additionally, the dissymmetry Z decreased appreciably with increasing q. The conformational change of the complex with q was characterized by the changes in the contour and persistence lengths of the chain and in the optical anisotropy of the scattering segments, which were obtained from numerical computations based on the polarized scattering equation for a wormlike-chain model with a restriction by the entropy force of the chain. The viscosity of the complex solution decreased with increasing q; above q ? 0.7 it increased strikingly. The conformational change of the complex with q was characterized by the change in exponent α in the Houwink-Mark-Sakurada equation [η] = KM^α. It was concluded that the iodine-saturated complex has the characteristics of a rod, regardless of the complex concentration.     

Conformation of cobrotoxin in aqueous solution as studied by nuclear magnetic resonance.

The 270-MHz proton NMR spectra of cobrotoxin from Naja naja atra were observed in 2H2O solution. The pKa value (5.93) of His-32 is slightly lower than the pKa value (6.65) of the reference model of N-acetylhistidine methylamide, because of the electrostatic interaction with Arg-33 and Asp-31. The pKa value (5.3--5.4) of His-4 is appreciably low, because of the interaction with the positively charged guanidino group possibly of Arg-59. The hydrogen-deuterium exchange rates in 2H2O solution were measured of cobrotoxin and imidazole-bearing models. The second-order rate constants of N-acetylhistidine methylamide, N-acetylhistidine and imidazole acetic acid satisfy the Br?nsted relation. With reference to this Br?nsted relation, the imidazole ring of His-32 is confirmed to be exposed. The imidazole ring of His-4 is also exposed and the exchange rate is excessively promoted by the presence possibly of Arg-59 in the proximity. All the methyl proton resonances are assigned to amino-acid types, by conventional double-resonance method and more effectively by the spin-echo double-resonance method. Eight methyl proton resonances are identified as due to the gamma and/or delta-methyl groups of Val-46, Leu-1, Ile-50 and Ile-52 residues. The proximity of aromatic ring protons and methyl protons is elucidated by the analyses of nulcear Overhauser effect enhancements. The aromatic proton resonances of Trp-29 are affected by the ionizable groups of Asp-31, His-32 and Tyr-35. The methyl groups of Ile-50 are in the proximity to the aromatic ring of Trp-29 and the methyl groups of Ile-52 are in the proximity to Tyr-25. The highest-field methyl proton resonance is due to a threonine residue in the proximity to His-4. The appreciable temperature-dependent chemical shift of this methyl proton resonance suggests a temperature-dependent local conformational equilibrium around the His-4 residue of the first loop of the cobrotoxin molecule.     

The interaction between vitamin B-12 and micelles in aqueous solution.

The apparent pK for benzimidazole displacement of a number of cobalamins is markedly affected by the presence of sodium lauryl sulfate micelles. However, micelles of cetyltrimethylammonium bromide or Triton X have little or no effect on the pK. By measuring the apparent pK as a function of sodium lauryl sulfate concentration, the association constants between the micelles and both base on and base off methylcobalamin were calculated. This calculation indicates that the base off form is strongly associated with the micelle while the base on form is not.     

Conformation of myelin basic protein in aqueous solution from nuclear magnetic resonance spectroscopy

High resolution ¹³C and ¹H NMR spectra of myelin basic protein over a range of pH and concentration indicate that intramolecular folding of the polypeptide chain occurs in the region of residues 8–116. As the pH is raised and the net charge on the protein decreased, intermolecular aggregation occurs between these same regions. The residues 81–118 are invariant in different species and this region is the locus of several chemical specificities of the protein.     

Influence of nonionic surfactant on aggregation state of scleroglucan in aqueous solution

The interactions between nonyl phenol polyethylene oxide and scleroglucan are investigated by turbidimetry, viscosimetry filterability tests and measurements of elastic modulus and adsorption. The phase diagrams of this ternary system have been established as a function of temperature and composition. It is shown that the surfactant molecules are adsorbed by the polymer at a low surfactant concentration, c_s; the adsorption induces a breaking down of the polymer aggregates and the filterability properties of the solutions are greatly improved. An excess of surfactant phase separation is observed by heating at a temperature that is a decreasing function of c_s. This is explained by the formation of a complex polymer-surfactant which has the same thermodynamic properties (lower critical solution temperature) as polyethylene oxide and the derived nonionic surfactants.