Cubic phases of gangliosides in water: possible role of the conformational bistability of the headgroup

An accurate X-ray scattering study of the self-association properties in water of the ganglioside GM1, a biological amphiphile similar to phospholipids but with an oligosaccharide headgroup, is described. The phase diagram displays a large cubic region, for concentrations between 31% and 55% by weight, enclosed by isotropic micellar and lamellar phases. The peculiar feature of the GM1 molecule to present a conformational bistability, recently observed in ganglioside micelles, can be well recognized in the cubic phase region, suggesting that GM1-water behaves like a pseudoternary system, with an additional degree of freedom, automatically readjusting the mole fraction of the two conformers in order to optimize the molecular packing

The effect of temperature on interacting micelles of gangliosides in water

Micellar solutions of the ganglioside GM1 are studied as a function of temperature in the concentration range 0.003-0.30 g CM-3 in water with light and x-ray scattering. In a narrow temperature range around 50-degrees-C, the micelles decrease their aggregation number from 300 to 235. The solution structuring, which is due to the electrostatic interactions among micelles, is found to be strongly affected by the micellar change. For instance, at high concentration the isotropic micellar solution at 25-degrees-C transforms into a primitive cubic phase at 60-degrees-C

Dependence of the form factor of ganglioside micelles on a conformational change with temperature

The gangliosides GM2, GM1 and GD1b, biological amphiphiles with a double tail hydrophobic part and an oligosaccharide chain headgroup, form micelles in solution. Light scattering experiments have shown that ganglioside micelles which have gone through a temperature cycle have a smaller molecular mass and hydrodynamic radius than those which have been kept at room temperature. This fact has been interpreted with the hypothesis that, with temperature, the ganglioside molecules undergo a conformational change which affects their micellar properties appreciably. Careful small angle X-ray experiments, aimed to confirm the light scattering data and to evidence differences in the micellar internal structure are presented. Ganglioside micelles are quite inhomogeneous particles with respect to X-ray scattering, since there is a large contrast variation between the inner lipid part and the external hydrated sugar layer. Experimental form factors are fitted with a double-shell oblate-ellipsoid model

Scattering techniques and ganglioside aggregates: Laser light, neutron, and X-ray scattering

Scattering techniques are applied to studying the structural features of ganglioside aggregates in solution. Here it is described how different probing radiations allow to access different structural and dynamical parameters on different lengthscales. Besides a brief but comprehensive description of the scattering measurements, several practical suggestions are given concerning the experiments and the data analysis