Expert Reviews in Molecular Medicine: http://www.expertreviews.org/
Accession information: DOI: 10.1017/S1462399402005409; 20 December 2002
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Structure-based classification of membrane lipids

Jacques Fantini, Nicolas Garmy, Radhia Mahfoud and Nouara Yahi

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Figure 1. Structure-based classification of membrane lipids. Plasma membrane lipids comprise phospholipids, glycolipids and sterols. More specifically, these lipids can be categorised as glycerophospholipids (GPLs), sphingolipids and cholesterol. (It should be noted that GPLs have been erroneously referred to as ‘phospholipids’ – this is incorrect as not all phospholipids contain glycerol.) (a) GPLs are the major component of membrane lipids. GPLs differ from each other with respect to polar head groups (the X group coming from an alcohol X-OH) whose OH group is esterified to the sn-3 carbon of glycerol. The main X-OH molecules are choline, ethanolamine, serine, glycerol and inositol. In GPLs, the fatty acid at sn-1 has a saturated chain with 16 or 18 carbon atoms. At sn-2, the fatty acid is generally longer (at least 18 carbon atoms) and is always unsaturated, with one or more cis double bonds (b) The phospholipids sphingomyelin (SM) and phosphatidylcholine (PC) share the same polar head group (i.e. phosphorylcholine) but differ in their hydrophobic moiety. The backbone structure of sphingolipids contains a sphingosine unit, and a saturated fatty acid with a long chain (up to 24 carbon atoms) is linked to the amino group of sphingosine via an amide linkage. This acyl chain is often 2-hydroxylated (as shown in the GalCer molecule). The acylated sphingosine is referred to as a ceramide. When a sugar or an oligosaccharide is linked by a b-glycosidic bond to the 1-OH group of ceramide, a glycosphingolipid (GSL) results. GSLs containing sialic acids in their carbohydrate moiety are called gangliosides. (c) The polar head group of cholesterol is a single OH group, whereas the hydrophobic moiety contains an iso-octyl carbon chain linked to a sterane-derived unit (fig001jfm).