1,721,033 research outputs found
Nuclear overhauser effect investigation on GM1 ganglioside containing N-glycolyl-neuraminic acid (II(3)Neu5GcGgOse(4)Cer)
No full textThe conformational properties of the oligosaccharide chain of GM1 ganglioside containing N-glycolyl-neuraminic acid, beta-Gal-(1-3)-beta-GalNAc-(1-4)-[alpha-Neu5Gc-(2-3)]-beta-Gal-(1-4)-beta-Glc-(1-1)-Cer, were studied through NMR nuclear Overhauser effect investigations on the monomeric ganglioside in dimethylsulfoxide, and on mixed micelles of ganglioside and dodecylphosphocholine in water. Several interresidual contacts for the trisaccharide core -beta-GalNAc-(1-4)-[alpha-Neu5Gc-(2-3)]-beta-Gal- were found to fix the relative orientation of the three saccharides, while the glycosidic linkage of the terminal beta-Gal- was found to be quite mobile as the beta-Gal-(1-3)-beta-GalNAc- disaccharide exists in different conformations. These results are similar to those found for two GM1 gangliosides containing N-acetyl-neuraminic acid and neuraminic acid [1]
AGGREGATION PROPERTIES OF SEMISYNTHETIC GD1A GANGLIOSIDE (IV(3)NEU5ACII(3)NEU5ACGGOSE(4)CER) CONTAINING AN ACETYL GROUP AS ACYL MOIETY
No full textGD1a ganglioside containing an acetyl group as acyl moiety, GD1a(acetyl), was synthesized from natural GD1a. The aggregative properties in aqueous solution of GD1a(acetyl) have been studied by static and dynamic laser light-scattering measurements. GD1a(acetyl) spontaneously aggregates as small micelles showing a hydrodynamic radius and molecular mass of 33 Angstrom and 96 kDa, respectively. Vibrio cholerae sialidase showed a very high activity on the micelles of GD1a(acetyl), compared to GD1a. This has been explained as a consequence of the high surface curvature of the the small micelles. High resolution proton NMR spectra were recorded from micelles of GD1a(acetyl) in deuterated water. The low overall correlation time of the GD1a(acetyl) micelles was calculated to be about 2 x 10(-8) s, a value one order of magnitude lower than that determined for natural GD1a
H-1-NMR STUDY ON GANGLIOSIDE AMIDE PROTONS - EVIDENCE THAT THE DEUTERIUM-EXCHANGE KINETICS ARE AFFECTED BY THE PREPARATION OF SAMPLES
No full textThe kinetics of H/H-2 chemical exchange of the amide proton has been suggested as one of the tools available for investigating hydrogenbond stabilizing interactions in gangliosides. The amide proton/deuterium (NH/H-2) exchange rates in GM2 ganglioside were studied by H-1-NMR spectroscopy on 12 samples prepared following different procedures. In samples passed through a sodium salt Chelex-100 cation exchange resin column prior to being analysed the N-acetylneuraminic acid NH exchange occurred in less than 10 min and that of ceramide NH in 30 min. The N-acetylgalactosamine acetamido NH exchange was slower, the half-life of the signal ranging from 15 min to 3.5 h. Contact of the Chelex-treated GM2 samples with water, through a dialysis process, modified the NH/H-2 exchange rate values, the N-acetylgalactosamine acetamido NH exchange becoming faster than that of ceramide NH and similar to that of N-acetylneuraminic acid NH. Our results indicate that the deuterium/proton exchange rate strongly depends on sample preparation (ion content and minor contaminants present in water). The three-dimensional model involving the N-acetylgalactosamine acetamido NH and the N-acetylneuraminic acid carboxyl group hydrogen-bonding, which is supported by experimental evidence, cannot be confirmed by NH-exchange measurement
Dynamics and spatial organization of surface gangliosides
No full textModel surfaces in a water environment suitable for the study of membrane ganglioside properties have been developed. They, together with ganglioside micelles of large molecular mass, consist of ganglioside-phosphatidylcholine mixed micelles of small molecular mass and ceramide-modified ganglioside micelles of intermediate molecular mass. The experimental information on the conformational and geometrical properties of ganglio-series gangliosides inserted into these model surfaces is discussed, compared and integrated with that obtained using multilamellar aggregate models. The results show that the conformational properties of the chain are determined by interresidual interactions between the sialic acid and N-acetylgalactosamine units, regardless of the total oligosaccharide structure, the structure of the ganglioside ceramide, possible phospholipid head group or Ca++ interactions, a highly enriched ganglioside environment, the presence of cholesterol in the membrane or temperature variation. Furthermore, the oligosaccharide chain seems to be well extended beyond the bilayer surface with a well defined average conformation and motional order, common to all the investigated gangliosides
Thermal fluctuations of small vesicles: observation by dynamic light scattering
No full textThe laser light scattering technique can be used in a nonconventional fashion to study dynamic properties of vesicles which are too small to be observed by microscopy. In fact, in suitable experimental conditions, the correlation function of the scattered light contains a contribution from bilayer fluctuations, besides the usual diffusion one. Characteristic fluctuation times have been determined for single-component phospholipid vesicles of 60 nm radius, prepared by extrusion. The addition of small amounts of a glycolipid (to 2% mole fraction), induces a significative increase in the fluctuation times (of the order of 20%) but still does not affect the diffusive motion, indicating a softening of the membrane. Being so sensitive, this technique is quite promising both for the study of membrane properties in the presence of defects and for applications to biology and pharmacology
Isolation and structural characterization of N-acetyl- and N-glycolylneuraminic-acid-containing GalNAc-G(D1a) isomers, IV(4)GalNAcIV(3)Neu5AcII(3)Neu5GcGgOse(4)Cer and IV(4)GalNAcIV(3)Neu5GcII(3)Neu5AcGgOse(4)Cer, from bovine brain
No full textA ganglioside preparation containing two structurally related minor gangliosides (Gg 1 + 2) was isolated from bovine brain ganglioside mixture and characterized. Treatment of 50 g ganglioside mixture with Clostridium perfrigens sialidase, followed by chromatography on DEAE-Sepharose and silica gel columns, yielded 20 mg Gg 1 + 2. By chemical analysis H-1- and C-13-NMR spectroscopy, enzymic hydrolyses using human beta-hexosaminidase A and clostridial sialidase, and TLC overlay with the conjugated cholera toxin B subunit, the two novel gangliosides Gg 1 and Gg 2 were identified to be: Gg 1, GalNAc-G(Dla)(Neu5Ac/Neu5Gc), beta-GalNac-(1-4)-[alpha-Neu5ac-(2-3)]-beta-Gal-(1-3)-beta-GalNAc-(1-4)-[alpha-Neu5Gc-(2-3)]-beta-Gal-(1-4)-beta-Glc-(1-1)-Cer; Gg 2, GalNac-G(Dla)(Neu5Gc/Neu5Ac), beta-GalNac-(1-4)-[alpha-Neu5Gc-(2-3)]-beta-Gal-(1-3)-beta GalNac-(1-4)-[alpha-Neu5Ac-(2-3)]-beta-Gal-(1-4)-beta-Glc-(1-1)-Cer. The two gangliosides contain the identical pentasaccharide backbone except that the substition of the two sialic acids, Neu5Ac and Neu5Gc, are in the reversed position of the external and the internal Gal residues. Our analyses showed that the content of Gg1 and Gg2 were approximately 0.12% and 0.08%, respectively, of the total brain ganglio-side mixture
Self-assembly in glycolipids
No full textThe interest in the glyco-world is widespread and covers quite a number of different areas. We restrict ourselves to underline some features concerning interactions and organization in the hydrophilic region of glycolipid aggregates that, besides the biological or technological aspects, constitute an experimental and theoretical challenge, as they invest some aspects of colloidal self-assembly that keep on being not completely understood
Microscopic structure of phospholipid bilayers: comparison between molecular dynamics simulations and wide angle X-ray spectra
No full textWe present results of molecular dynamics simulations of fully hydrated dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine bilayers in the disordered liquid crystalline phase (Lalpha) and compare them to wide-angle X-ray scattering experiments. Though we find a generally good agreement between the simulated and experimental spectra, there are some deviations whose origin has been investigated by a reparametrization of the aliphatic chains' force field. A detailed analysis of the various contribution to the X-ray spectra shows that a non-negligible contribution to the total scattered intensity comes from the headgroups and the head-tail cross correlation
Modeling ganglioside headgroups by conformational analysis and molecular dynamics
No full textThe conformations and dynamics of gangliosides GM1, GM2, 6'-GM2 and GM4 have been studied by computational means, and the results compared to NMR data. Unconstrained conformational searches were run using the AMBER* force field augmented by MNDO derived parameters for the Neu5Ac anomeric torsion, the GB/SA water solvation model, and the MC/EM alogorithm; extended (10-12[emsp4 ]ns) dynamic simulations in GB/SA water were performed with the MC/SD protocol, and the stored structures were minimized. The overall mobility of the Neu5Ac alpha2,3Gal linkage and the position of its minimum energy conformation have been shown to depend mainly on the presence or the absence of a GalNAc residue at the adjacent position. The best quantitative agreement with the available NOE data was achieved after minimization of the structures stored during the MC/SD dynamic runs. The latter protocol appears to reproduce satisfactorily the available experimental data, and can be used with confidence to build three-dimensional models of ganglioside headgroups
Multilevel structuring of ganglioside-containing aggregates : from simple micelles to complex biomimetic membranes
No full textWe revisit the structural investigation we performed over the years on gangliosides, biological amphiphiles typically found in the cell membranes of the nervous system of mammalians. Their molecular features, a large and charged saccharidic headgroup connected to a sticky and extended ceramide double tail, strongly dictate their aggregation properties and place ganglioside aggregates at the borderline between the curved world and the flatland. All along we found that unexpected interesting behaviours were induced by the hierarchical propagation of such extreme monomer properties, from the aggregate scale to the mesoscopic phases. In fact, even small changes in the monomer geometry or hindrance result in dramatic aggregate reshaping, due to collective amplification. Surface packing optimization requires preferential mutual orientation of headgroups, giving rise to trapped solid-disordered configurations. The interplay between interparticle and intraparticle interactions gives rise to unexpected behaviours and counterintuitive phase's landscape. In situ modification of monomer properties, operated by enzymatic digestion of aggregated ganglioside headgroups, either causes collective rearrangement or is overwhelmed by collective trapping, depending on their surface density. This aspect is interesting as gangliosides are not evenly distributed in cell membranes, but only in the outer leaflet, where they p]articipate in rafts, functional microdomains enriched in special lipids including cholesterol. We recently found that ganglioside GM1 forces a preferential distribution of cholesterol, constituting a collective structural pair across the membrane. In summary, ganglioside assemblies, through cooperativity, reach a structural complexity comparable or even bigger and more adaptive than that of a protein
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