Enhancement by Gangliosides of the Binding of Serotonin to Serotonin Binding Protein

Abstract: Several gangliosides, especially G_D3 (disialosyllactosyl ceramide) in the presence of another lipid (lecithin) were found to enhance the binding of serotonin to serotonin binding protein (SBP) severalfold. In our conditions, this enhancement was linear to a concentration of 2.7 × 10^?6I G_D3 and a three- to fivefold increase in binding capacity of SBP was obtained with 8.8 × 10^?6 M. The addition of this ganglioside led to an increase of serotonin binding sites, but not to an increase in the affinity of SBP to serotonin. Optimal binding capacity was found with a ratio of lecithin to ganglioside of 6: 1 (w/w). No binding was found in the absence of either SBP or Fe²⁺ (binding of serotonin to SBP is dependent on Fe²⁺). Other glycosphingolipids (sulfatide, G_D1a, G_D1b, G_M1) showed lesser effects at low concentration, whereas asialo-G_M1, cytolipin H, galactocerebroside and G_M3 had insignificant effects. Since earlier studies suggested a storage role for serotonin binding protein, the interaction of gangliosides with this protein may regulate the concentration of the biogenic amine in the synapse.