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Results for “Scattering, Small Angle”

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PubMed1993

Small angle X-ray scattering: possibilities and limitations in characterization of vesicles.

The use of small angle X-ray scattering (SAXS) for characterization of lipid vesicle dispersions is described. The effect of curvature of the membrane, the presence of proteins in the core and on the surface of the membrane, variations in membrane thickness and distribution in the number of bilayers of the vesicles in the dispersion on the scattering curve is discussed. Concerning unilamellar vesicles, either the membrane curvature of vesicles smaller than 50 nm or variations in membrane thickness result in a disappearance of the first node in the scattering curve, even if the bilayer is symmetric with respect to the electron density distribution. In the case of dispersion in which unilamellar as well as multilamellar vesicles are present it is shown that a small fraction of multilamellar liposomes changes the scattering curve dramatically. Liposomes were prepared from various compositions of dipalmitoylphosphatidylcholine (DPPC) and cholesterol hemisuccinate (CHEMS) by the film method. The electron density profile of the bilayers and distribution in the number of bilayers of the liposome dispersions were determined. The average number of bilayers increased as a function of the decrease in CHEMS content. Liposomes with higher CHEMS content than 10 mol% were unilamellar. It seems that increase in charge intercalated in the bilayers resulted in unilamellar vesicles.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2005

Refinement of multidomain protein structures by combination of solution small-angle X-ray scattering and NMR data.

Determination of the 3D structures of multidomain proteins by solution NMR methods presents a number of unique challenges related to their larger molecular size and the usual scarcity of constraints at the interdomain interface, often resulting in a decrease in structural accuracy. In this respect, experimental information from small-angle scattering of X-ray radiation in solution (SAXS) presents a suitable complement to the NMR data, as it provides an independent constraint on the overall molecular shape. A computational procedure is described that allows incorporation of such SAXS data into the mainstream high-resolution macromolecular structure refinement. The method is illustrated for a two-domain 177-amino-acid protein, gammaS crystallin, using an experimental SAXS data set fitted at resolutions from approximately 200 A to approximately 30 A. Inclusion of these data during structure refinement decreases the backbone coordinate root-mean-square difference between the derived model and the high-resolution crystal structure of a 54% homologous gammaB crystallin from 1.96 +/- 0.07 A to 1.31 +/- 0.04 A. Combining SAXS data with NMR restraints can be accomplished at a moderate computational expense and is expected to become useful for multidomain proteins, multimeric assemblies, and tight macromolecular complexes.

Computational Biology↗

PubMed2002

Quaternary structure built from subunits combining NMR and small-angle x-ray scattering data.

A new principle in constructing molecular complexes from the known high-resolution domain structures joining data from NMR and small-angle x-ray scattering (SAXS) measurements is described. Structure of calmodulin in complex with trifluoperazine was built from N- and C-terminal domains oriented based on residual dipolar couplings measured by NMR in a dilute liquid crystal, and the overall shape of the complex was derived from SAXS data. The residual dipolar coupling data serves to reduce angular degrees of freedom, and the small-angle scattering data serves to confine the translational degrees of freedom. The complex built by this method was found to be consistent with the known crystal structure. The study demonstrates how approximate tertiary structures of modular proteins or quaternary structures composed of subunits can be assembled from high-resolution structures of domains or subunits using mutually complementary NMR and SAXS data.

Calmodulin↗

PubMed1994

Small-angle x-ray scattering study of dispersed crystals from bone and tendon.

A small-angle x-ray scattering study of dispersed crystals from rat bone and mineralized turkey tendon shows that the particles in both preparations have the same scattering behavior. The data are very similar to those reported by Fratzl et al. for intact turkey tendon and are consistent with the crystals being plate shaped. These observations have important implications for understanding both the structure and mineralization processes of these tissues.

Animals↗

PubMedDate not supplied

A small angle X-ray scattering study of the binding of cyclosporin-A to calmodulin.

Small angle X-ray scattering (SAXS) was applied to the binding of the immunosuppressant drug cyclosporin-A to the protein calmodulin. Guinier analysis of the SAXS profiles yielded a radius of gyration, Rg, of 19.7 +/- 0.3 A for the native protein and 16.9 +/- 0.3 A for the drug/protein complex. Maximum entropy (maxent) methods of data analysis were used to calculate the distance distribution function, p(r). From this analysis, the Rg for the native protein is 20.9 +/- 0.1 A and that for the complex 16.7 +/- 0.1 A. The measured SAXS profiles and the derived p(r) for calmodulin agree with profiles calculated from the crystallographic structure of calmodulin. Major structural changes are induced in calmodulin on binding cyclosporin-A. A model consistent with the observed scattering profiles is an ellipsoid with major axes 55 and 36 A. Molecular modeling of the calmodulin molecule suggests that bond rotation in the flexible alpha-helix linker region produces models consistent with the above observations.

Animals↗

PubMed2006

Interaction of phenothiazine compounds with zwitterionic lysophosphatidylcholine micelles: Small angle X-ray scattering, electronic absorption spectroscopy, and theoretical calculations.

In this work, small-angle X-ray scattering (SAXS) studies on the interaction of the phenothiazine cationic compounds trifluoperazine (TFP, 2-10 mM) and chlorpromazine (CPZ, 2-10 mM) with micelles of the zwitterionic surfactant L-alpha-lysophosphatidylcholine (LPC, 30 mM), at pHs 4.0 and 7.0, are reported. The SAXS results demonstrate that, upon addition of both phenothiazines, the LPC micelle of prolate ellipsoidal shape changes into a cylindrically shaped micelle, increasing its axial ratio from 1.6 +/- 0.1 (in the absence of drug) to 2.5 +/- 0.1 (for 5 and 10 mM of phenothiazine). Such an effect is accompanied by a shrinking of the paraffinic shortest semiaxis from 22.5 +/- 0.3 to 20.0 +/- 0.5 A. Besides, a significant increase in polar shell electron density from 0.39(1) to 0.45(1) e/A3 is observed, consistent with cylinder-like aggregate geometry. Moreover, an increase of the phenothiazine concentration induces the appearance of a repulsive interference function over the SAXS curve of zwitterionic micelles, which is typical of interaction between surface-charged micelles. Such a finding provides evidence that the positively charged phenothiazine molecule must be accommodated near the hydrophobic/hydrophilic inner micellar interface in such a way that a net surface charge is altered with respect to the original overall neutral zwitterionic micelle. Such phenothiazine location is favored by both electrostatic and hydrophobic contributions, giving rise to binding constant values, obtained from electronic absorption results, that are quite larger compared to their binding to another zwitterionic surfactant, 3-(N-hexadecyl-N,N-dimethylammonio)propanesulfonate (HPS) (Caetano, W., et al. J. Colloid Int. Sci. 2003, 260, 414-422). Comparisons are made by means of theoretical calculations of the surfactant headgroup dipole moments for monomers of LPC and HPS. The theoretical results show that the dipole moment in LPC is almost perpendicular to the methylene chain, while a significant contribution along the methylene chain occurs for HPS. Besides, evidence is presented for extensive delocalization of the charges in the headgroups, which could be also relevant for the binding of the drugs.

Lysophosphatidylcholines↗

PubMed2000

Small angle X-ray scattering reveals a compact intermediate in RNA folding.

We have used small angle X-ray scattering (SAXS) to monitor changes in the overall size and shape of the Tetrahymena ribozyme as it folds. The native ribozyme, formed in the presence of Mg2+, is much more compact and globular than the ensemble of unfolded conformations. Time-resolved measurements show that most of the compaction occurs at least 20-fold faster than the overall folding to the native state, suggesting that a compact intermediate or family of intermediates is formed early and then rearranges in the slow steps that limit the overall folding rate. These results lead to a kinetic folding model in which an initial 'electrostatic collapse' of the RNA is followed by slower rearrangements of elements that are initially mispositioned.

Animals↗

PubMed2005

Annular arrangement and collaborative actions of four domains of protein-disulfide isomerase: a small angle X-ray scattering study in solution.

We presented for the first time a small angle x-ray scattering study of intact protein-disulfide isomerase (PDI) in solution. The restored model revealed that PDI is a short and roughly elliptical cylinder with a molecular mass of 69 kDa and dimensions of 105 x 65 x 40 A, and the four thioredoxin-fold domains in the order a-b-b'-a' are arranged in an annular fashion. Atomic force microscope imaging also supported the finding that PDI appears as an approximately flat elliptical cylinder. A PDI species with apparent molecular mass of 116 kDa measured by using size-exclusion chromatography, previously assumed to be a dimer, was determined to exist mainly as a monomer by using analytical ultracentrifugation. The C-terminal fragment 441-491 contributed to the anomalous molecular mass determination of PDI by size-exclusion chromatography. The annular model of PDI accounted for the cooperative properties of the four domains in both the isomerase and chaperone functions of PDI.

Crystallography, X-Ray↗

PubMed1991

Structural investigations of human stratum corneum by small-angle X-ray scattering.

The structure of human stratum corneum was investigated with small-angle X-ray scattering (SAXS). At room temperature the scattering curve was characterized by a strong intensity at low scattering vector (Q less than 0.8 nm-1) and two complicated diffraction peaks originating from a lamellar structure of the lipids. The lamellar lipid structure in the stratum corneum transformed to a disordered structure between 65 degrees C and 75 degrees C, the same temperature region at which a thermal lipid transition occurred. After cooling down to room temperature a recrystallization of at least a part of the lipids took place, after which only one unit cell with a repeat distance of 13.4 nm could be detected. Comparison of the scattering curve of the stratum corneum after crystallization with the scattering curve of the stratum corneum before recrystallization leads to the conclusion that in the original curve the lipids are arranged in two unit cells with repeat distances of 6.4 nm and 13.4 nm. From model calculations it appears that the latter unit cell consists of more than one bilayer. The scattering curves of stratum corneum hydrated to various levels were measured. A change in the water content of stratum corneum between 6% w/w and 60% w/w (fully hydrated) did not result in swelling of the bilayers, but the scattering curve obtained with stratum corneum hydrated to 60% w/w differed from those at lower hydration levels: the scattering curve at 60% w/w showed only the diffraction peaks corresponding to a unit cell with a repeat distance of 6.4 nm. This observation implies that the ordering of a part of the lipids is reduced at very high water contents, which may explain the strong penetration-enhancing effects of water in the stratum corneum.

Crystallization↗

PubMed1983

A small angle x-ray scattering study of a rhodopsin-lipid complex in hexane.

A small angle x-ray scattering study of a rhodopsin-lipid complex in hexane demonstrates the presence of two distinct particle populations with corresponding radii of gyration of approximately 22 and 160 A. A model based on the existence of inverted lipid micelles surrounding the protein polar moieties while the protein hydrophobic domains act as cross-links between the inverted micelles is presented. It accounts for the results herewith reported and explains most of the properties hitherto characterized for the rhodopsin-lipid complex in hexane.

Animals↗

PubMed2006

Tetrameric structure of thermostable direct hemolysin from vibrio parahaemolyticus revealed by ultracentrifugation, small-angle X-ray scattering and electron microscopy.

The thermostable direct hemolysin (TDH) is a major virulence factor of Vibrio parahaemolyticus. We have characterized the conformational properties of TDH by small-angle X-ray scattering (SAXS), ultracentrifugation and transmission electron microscopy. Sedimentation equilibrium and velocity studies revealed that the protein is tetrameric in aqueous solvents. The Guinier plot derived from SAXS data provided a radius of gyration of 29.0 A. The elongated pattern with a shoulder of a pair distance distribution function derived from SAXS data suggested the presence of molecules with an anisotropic shape having a maximum diameter of 98 A. Electron microscopic image analysis of the negatively stained TDH oligomer showed the presence of C(4) symmetric particles with edge and diagonal lengths of 65 A and 80 A, respectively. Shape reconstruction was carried out by ab initio calculations using the SAXS data with a C(4) symmetric approximation. These results suggested that the tetrameric TDH assumes an oblate structure. The hydrodynamic parameters predicted from the ab initio model differed slightly from the experimental values, suggesting the presence of flexible segments.

Bacterial Toxins↗

PubMed1992

Small-angle X-ray scattering study by synchrotron orbital radiation reveals that high molecular weight subunit of glutenin is a very anisotropic molecule.

Small-angle X-ray scattering of one high molecular weight (HMW) subunit of wheat glutenin was measured at protein concentration ranges from 1.0 to 10.0 mg/ml. The radius of gyration of whole particles, RO, in aq. 50% (v/v) 1-propanol and 0.1M acetic acid was 16.6 +/- 0.1nm and 22.8nm, respectively, and the corresponding radius of gyration of the cross-section, RC, was 2.82 +/- 0.02 nm and 2.23 +/- 0.01 nm, which indicate that the glutenin HMW subunit exists as very anisotropic particles in both solutions. The RO and RC values of the subunit, and the drastic decrease in scattered intensity at small angles that occurs in the acetic acid solution with relatively low protein concentration are completely explained in terms of rod-like molecules of the glutenin HMW subunit.

Glutens↗

PubMed2005

Application of small angle X-ray scattering (SAXS) for differentiation between normal and cancerous breast tissue.

INTRODUCTION: Small angle, between 3 degrees and 10 degrees, X ray scattering is predominantly coherent giving rise to diffraction effects that can be observed as constructive and destructive interferences. These interferences carry information about the molecular structure of the tissue and hence can be used to identify changes that occur due to cancer. METHOD: In this study an energy dispersive X-ray diffraction method was used. The optimum scattering angle, determined from a series of measurements on adipose breast tissue at several angles from 4 to 7.3 degrees, was found to be 6.5 degrees. Once optimized the system was used to measure the diffraction profiles (corrected scattered intensity versus momentum transfer) of a total of 99 breast tissue samples. The samples were both normal and tumour samples. RESULTS: Adipose tissue showed a sharp, high intensity peak at low momentum transfer values of approximately 1.1nm-1. Adipose tissue, mixed tissue (adipose & fibroglandular) and tumor have peaks at different values of momentum transfer that can be used to identify the tissue. Benign and malignant breast tissues can also be differentiated by both peak positions and peak heights. It was also observed that the results were reproducible even after the tissue had been preserved at liquid nitrogen temperatures. CONCLUSION: We were able to differentiate between normal, benign and malignant breast tissues by using energy dispersive small angle x-ray scattering.

Journal Article↗

PubMed2002

The pore structure in processed Victorian Brown coal.

Changes in the pore structure of Victorian Brown coal when upgraded with heated gases under pressure are investigated. We show that the results obtained from ultra-small-angle neutron scattering (USANS) measurements agree with previous results using small-angle X-ray scattering results but that USANS may also be used to investigate the meso porosity. Findings from small-angle scattering are confirmed using electron microscopy. We also show evidence from electron diffraction that thermal conditions within the brown coals during the upgrade procedure may be far more extreme than previously thought.

Journal Article↗

PubMed1997

Small-angle X-ray scattering analysis of pneumococcal lipoteichoic acid phase structure.

X-Ray-scattering analysis was performed on micelles of lipoteichoic acid from Streptococcus pneumoniae. This lipoteichoic acid differs from poly(glycerophosphate) and poly(glycosylglycerophosphate) lipoteichoic acids by a unique positively charged diacylglyceroglycolipid anchor and a complex structure of the hydrophilic chain which is composed of zwitterionic tetrasaccharide ribitol phosphate repeats each carrying two zwitterionic phosphocholine substituents. The size distribution of the lipoteichoic acid micelles was sufficiently homogenous to determine their size and some related molecular parameters by small-angle scattering analysis. Nearly independent on the ionic strength of the aqueous dispersion, an average micelle contained about 150 lipoteichoic acid molecules arranged in a spherical assembly with a diameter of about 23 nm, whereby the hydrophilic region occupied an outer shell of about 8.5 nm thickness. Taken this as the average chain length of LTA in the micelle and 7.2 repeats per chain, each repeat contributed about 1.2 nm to the thickness of the hydrophilic shell as compared to 2.4 nm for a fully extended chain conformation and 1.1 nm estimated for a more helical arrangement [Klein, R. A., Hartmann, R., Egge, H., Behr, T. & Fischer, W. (1994) Carbohydr. Res. 256, 189-222]. A comparison with the micelle of poly(glycerophosphate) lipoteichoic acid of Staphylococcus aureus suggests that the supramolecular structure is largely independent of the structure of the hydrophilic chain and solely dictated by the small cross-sectional area of the diacylglycerol moiety common to all lipoteichoic acids and lipoglycans of gram-positive bacteria.

Carbohydrate Sequence↗

PubMed2005

Simulation of small-angle x-ray scattering from collagen fibrils and comparison with experimental patterns.

Simulation of small-angle x-ray scattering from collagen in healthy and cancerous breast tissue may reveal detailed information on the structural changes in collagen. Collagen fibril is modelled as a cylinder with axially periodic step-function electron density, and packing is approximated by placing the cylinders in small hexagonal bundles. The intensity from a bundle is calculated by summing analytical scattering amplitudes from the cylinders, and intensities from several bundles with varying lattice constants are averaged. Comparisons with more complex models are made to estimate the robustness of the model. The oscillations in the equatorial direction are not significantly affected by added complexity. The relative intensities of the Bragg peaks in the meridional direction can be tuned by modifying the axial electron density distribution. Tests with different fibril radius distributions show that the average radius can be determined with an accuracy of +/-0.5 nm but that the shape of the radius distribution cannot be accurately determined from the scattering patterns. The effect of multiple scattering and the detector point-spread function (PSF) is considered, and the PSF may make a significant contribution to the final slope of the scattering pattern. Comparisons with observed scattering indicate that the model is basically correct at the supra-molecular level.

Breast↗

PubMed2005

A preliminary study of breast cancer diagnosis using laboratory based small angle x-ray scattering.

Breast tissue collected from tumour samples and normal tissue from bi-lateral mastectomy procedures were examined using small angle x-ray scattering. Previous work has indicated that breast tissue disease diagnosis could be performed using small angle x-ray scattering (SAXS) from a synchrotron radiation source. The technique would be more useful to health services if it could be made to work using a conventional x-ray source. Consistent and reliable differences in x-ray scatter distributions were observed between samples from normal and tumour tissue samples using the laboratory based 'SAXSess' system. Albeit from a small number of samples, a sensitivity of 100% was obtained. This result encourages us to pursue the implementation of SAXS as a laboratory based diagnosis technique.

Algorithms↗

PubMed2005

Quantitative analysis of lyotropic lamellar phases SANS patterns in powder oriented samples.

We have developed a detailed numerical method based on the Caillé model to fit Small Angle Neutron Scattering profiles of powder-oriented lyotropic lamellar phases. We thus obtain quantitative values for the Caillé parameter and the smectic penetration length from which we can derive the smectic compression modulus and the membrane mean bending modulus. Our method, applied to a surfactant lamellar phase system decorated by amphiphilic copolymers, provides excellent fits for any intermembrane spacing or membrane concentration over the entire q-range of the SANS experiments. We compare our fits with those obtained from the model of Nallet et al. (J. Phys. II 3, 487 (1993)), which is reviewed. Good fits are obtained with both methods for samples exhibiting "hard" smectic order (sharp Bragg peak, moderate small angle scattering). Only our procedure, however, gives good fits in the case of "soft" smectic order (smooth Bragg peak, strong small angle scattering). A quantitative criterion to discriminate between these "soft" and "hard" samples is also proposed, based on a simple analogy with smectic-A liquid crystal in contact with an undulating solid surface. This allows us to anticipate the type of thermodynamic information that can be derived from the fits.

Journal Article↗