page_title: Sulfatide
section_title: Synthesis and degradation
hierarchical_section_title: Sulfatide / Synthesis and degradation
caption_attribution_description: English: Synthesis of sulfatide
context_page_description: Sulfatide, also known as 3-O-sulfogalactosylceramide, SM4, or sulfated galactocerebroside, is a class of sulfolipids, specifically a class of sulfoglycolipids, which are glycolipids that contain a sulfate group. Sulfatide is synthesized primarily starting in the endoplasmic reticulum and ending in the Golgi apparatus where ceramide is converted to galactocerebroside and later sulfated to make sulfatide. Of all of the galactolipids that are found in the myelin sheath, one fifth of them are sulfatide. Sulfatide is primarily found on the extracellular leaflet of the myelin plasma membrane produced by the oligodendrocytes in the central nervous system and in the Schwann cells in the peripheral nervous system. However, sulfatide is also present on the extracellular leaflet of the plasma membrane of many cells in eukaryotic organisms.
  Since sulfatide is a multifunctional molecule, it can be used in multiple biological areas. Aside from being a membrane component, sulfatide functions in protein trafficking, cell aggregation and adhesion, neural plasticity, memory, and glial-axon interactions.
context_section_description: Sulfatide synthesis begins with a reaction between UDP-galactose and 2-hydroxylated or non-hydroxylated ceramide. This reaction is catalyzed by galactosyltransferase (CGT), where galactose is transferred to 2-hydroxylated, or non-hydroxylated ceramide, from UDP-galactose. This reaction occurs in the luminal leaflet of the endoplasmic reticulum, and its final product is GalCer, or galactocerebroside, which is then transported to the Golgi apparatus. Here, GalCer reacts with 3’-phosphoadenosine-5’-phosphosulfate (PAPS) to make sulfatide. This reaction is catalyzed by cerebroside sulfotransferase (CST). CST is a homodimeric protein that is found in the Golgi apparatus. It has been demonstrated that mice models lacking CST, CGT, or both are incapable of producing sulfatide indicating that CST and CGT are necessary components of sulfatide synthesis.
  Sulfatide degradation occurs in the lysosomes. Here, arylsulfatase A hydrolyzes the sulfate group. However, in order for this reaction to be carried out, a sphingolipid activator protein such as saposin B must be present. Saposin B extracts sulfatide from the membrane, which makes it accessible to arylsulfatase A. Arylsulfatase A can then hydrolyze the sulfate group. Accumulation of sulfatide can cause metachromatic leukodystrophy, a lysosomal storage disease and may be caused because of a defect in arylsulfatase A, leading to an inability to degrade sulfatide.
caption: Synthesis of sulfatide
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