Conformational preferences of the gangliosides GM1, GM1b, and GD1 a have been investigated by using a systematic combination of NMR distance constraints and molecular mechanics calculations. These gangliosides share a common four-sugar core but differ in the number or placement of sialic acid residues attached to the core. Placement of the sialic acid residues is shown to influence the preferred core conformation. The origin of these effects is postulated to be intramolecular interactions of the sialic acid residues with other remote residues. In the case of GM1, hydrogen bonds between the internal sialic acid and an TV-acetyl group on GalNAc are suggested. In the case of GD1a, a hydrogen-bonding network between the terminal and internal sialic acids is suggested to play a role.
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