Figure 1.

Pathways of human glycosphingolipid biosynthesis. Ceramide (Cer) is glucosylated to form glucosylceramide (GlcCer), which is elongated with a galactose to form lactosylceramide (LacCer). LacCer is the precursor for glycosphingolipid (GSL) elongation into multiple biosynthetic pathways, including the globo-, lacto/neolacto-, and ganglio-series. Sialylation of the GAL residue of LacCer by ST3GAL5 (GM3 synthase) generates the simplest ganglio-series GSL, known as GM3. GM3 is the essential precursor for the production of all a-, b-, and c- series gangliosides (large box, outlined in red). Of these gangliosides, four are the most abundant GSLs found in neural tissue, GM1a, GD1a, GD1b and GT1b (small box, outlined in black). Graphic representations of GSL monosaccharide residues are consistent with Symbol Nomenclature for Glycans guidelines (SNFG).