Hydration and thermal reversibility of glycolipids depending on sugar chains

Abstract

To elucidate a relationship between the structural properties and hydration characteristic of gangliosides, time-resolved small-angle X-ray scattering measurements using synchrotron radiation have been performed on aqueous dispersions of various types of gangliosides (G_M1, G_D1a, G_D1b and G_M3) under a constant heating (5–65 °C) and cooling (65–5 °C) rate. In the case of G_M3, they formed a vesicular aggregate with a high structural reversibility in the heating-and-cooling process. For the micelles of G_M1, G_D1a and G_D1b, we found an evident thermal hysteresis in the structural changes of their headgroups and evaluated quantitatively the amounts of water molecules occluded in the micellar hydrophilic regions by using the shell modeling method reported previously. For all cases of G_M1, G_D1a and G_D1b, the thickness of the hydrophilic region of the micelle shrunk after the heating process, and stayed mostly constant over the entire cooling range. On the other hand, the amounts of water molecules and the behavior of the G_M1, G_D1a and G_D1b micelles in the heating-and-cooling process greatly depended on the number of sialic acid residues in the sugar chain, that is, the penetration of water molecules was much more reversible for the G_M1 micelle compared with those for the G_D1a and G_D1b micelles. The observed clear hysteresis and the hydration characteristics of G_D1 gangliosides would relate to their role in neuronal membranes, where G_D1 gangliosides show the greatest concentrations.