Characteristics of thermotropic phase transition of glycosphingolipid (Ganglioside) aggregates in aqueous solution

In this report, by using synchrotron radiation X-ray small-angle scattering, we show the structural characteristics of the ganglioside aggregates depending on both the temperature and oligosaccharide chain. The experimental results of the aqueous solutions containing G(M1), G(D1), or crude mixture gangliosides show that the elevation of temperature induces the change of the micellar structure accompanied by the change of the internal scattering density distribution. These changes are well described by applying a shell-modeling method to the observed scattering curves since the shell-modeling method can determine the intramicellar structures. A noticeable common feature found in the thermotropic transition of the ganglioside micelles is the contraction of the micellar dimension resulting from the shrinkage of the hydrophilic region of the micelle. The shrinkage amounts to 20-30% of the thickness of the hydrophilic region, suggesting the structural change of the oligosaccharide chains of the gangliosides from an extended conformation to a compact one. The differences of the thermotropic stability depending on the number of the sialic acids of the oligosaccharide chain were also observed. The present results which suggest a thermal perturbation in the physiological range 20-50 degrees C induces a conformational change of the oligosaccharide chains of ganglioside molecules very sensitively. (C) 1998 Elsevier Science B.V.