Sphingolipids Dr. Abir Alghanouchi Biochemistry department Sciences college

Sphingolipids make up the second largest class of phospholipids. The most distinct difference between sphingolipids and glycerophospholipids is that the backbone of sphingolipids is NOT glycerol.

Sphingolipids contain: Sphingosine (shown in red), which is a long-chain amino alcohol:18- carbon amino alcohol with C-C double bond A fatty acid is joined to sphingosine via an amide linkage rather than an ester linkage as seen in glycerol.

Sphingosine may be reversibly phosphorylated to produce the signal molecule sphingosine-1-phosphate Other derivatives of sphingosine are commonly found as constituents of biological membranes. 4

The amino group of sphingosine can form an amide bond with a fatty acid carboxyl, to yield a ceramide. In the more complex sphingolipids, a polar “head group" is esterified to the terminal hydroxyl of the sphingosine moiety of the ceramide.  5

Sphingomyelin has a phosphocholine or phosphoethanolamine head group. Sphingomyelins are common constituent of plasma membranes Sphingomyelin, with a phosphocholine head group, is similar in size and shape to the glycerophospholipid phosphatidyl choline.

A cerebroside is a sphingolipid (ceramide) with a monosaccharide such as glucose or galactose as polar head group.

Sulfatide: Sugar is galactose with sulfate esterified at carbon 3 of galactose A ganglioside is a ceramide with a polar head group that is a complex oligosaccharide, including the acidic sugar derivative sialic acid. Cerebrosides, sulfatide and gangliosides, collectively called glycosphingolipids

Ceramide is a precursor for numerous glycosphingolipids: Non sphingolipids

Importance of Sphingolipids One well-known function of sphingolipids is that they function as cell surface antigens, defining the various blood types. The human blood groups are determined in part by the type of sugars located on the head groups. If the gene encodes a protein that transfers an N-acetylgalactosamine group, this corresponds to the A antigen.

Importance of Sphingolipids If the gene encodes a protein that transfers a galactose group, this corresponds to the B antigen. If the gene does not encode an active glycosyltransferase, this corresponds to the O antigen.

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