Cluster Organization of Glycosphingolipid GD1a in Lipid Bilayer Membranes:  A Dielectric and Conductometric Study

Abstract

The dielectric and conductometric properties of mixed ganglioside/phospholipid vesicle aqueous suspensions were measured in the frequency range from 10 kHz to 10 MHz, where a pronounced dielectric dispersion due to surface bilayer polarization occurs. The concentration of the ganglioside employed, a disialoglycosphingolipid GD1a, was varied from 50 to 500 μg/mL (corresponding to a molar ratio [GD1a]/[DPPC] from 0.2 × 10-3 to 2 × 10-3) and the excess surface polarizability, attributed to ganglioside organization within the lipid bilayer, was evaluated. The dependence of the ganglioside concentration shows that a clusterization process occurs, giving rise to the formation of large in-phase aggregates whose coordination number, of the order of a few hundred dipoles, depends on temperature. The relevance, from a biological point of view, of a nonuniform distribution of GD1a in a lipid bilayer membrane is briefly discussed.

Membrane Lipid Nanodomains

“…As a consequence, their phase characteristics will vary depending on the conditions of the model system. This variation is already evident in the literature where, for example, (i) GM 1 clusters present in monolayers with liquid condensed characteristics have been shown to behave as a liquid condensed phase, (ii) while in more disordered membranes, such as free-standing liquid disordered bilayers, the ganglioside domains display liquid disordered phase characteristics. , Ganglioside nanodomains can be found in membranes of diverse ordering of acyl chains (liquid condensed and liquid expanded, liquid crystalline ordered, and liquid crystalline disordered phases, Table ), and therefore, a simple common description of their ordering and dynamics cannot provided. ,, …”

“…54,55 Ganglioside nanodomains can be found in membranes of diverse ordering of acyl chains (liquid condensed and liquid expanded, liquid crystalline ordered, and liquid crystalline disordered phases, Table 4), and therefore, a simple common description of their ordering and dynamics cannot provided. 54,55,192 Gangliosides are typically thought of as cone-shaped molecules (Figures 8 and 11) due to the properties of their headgroup (geometry and charge). This can affect the topology of the membranes where they are inserted as the local concentration of gangliosides in a nanodomain can lead to the creation of local curvature.…”