2. GSL Synthesis and Turnover
GSL metabolism is accomplished along the endomembrane system (Figure 1). GSL synthesis starts in the endoplasmic reticulum (ER) where a sphingoid base is condensed with an
acyl-CoA, to generate Ceramide (Cer) [102,103] (Figure 1). In the ER, Cer can be galactosylated to produce galactosylceramide (GalCer) [104]. GalCer is, then, transported to the Golgi complex
where it can be sulphated to produce sulphogalactolipids, or sialylated to produce the GM4 ganglioside . Alternatively, Cer can be conveyed to the Golgi complex via transport vesicles or by the ceramide-transfer protein CERT [105]. CERT transports Cer to the trans-Golgi network (TGN) where it is primarily used for the synthesis of sphingomyelin (SM) (Figure 1). On the contrary, Cer transported to Golgi by vesicular transport is converted to glucosylceramide (GlcCer). GlcCer is synthesized by the addition of a glucose residue to Cer on the cytosolic leaflet of
cis-Golgi membranes and GlcCer is further glycosylated by the activity of glycosyltransferases distributed along Golgi cisternae, resulting in more than 300 species of GSLs. These enzymes transfer a specific carbohydrate from the appropriate activated sugar nucleotide (e.g., UDP-Galactose, CMP-sialic acid, UDP-Fucose, etc.) to the non-reducing end of the growing carbohydrate chain linked to GlcCer
2. GSL Synthesis and TurnoverGSL metabolism is accomplished along the endomembrane system (Figure 1). GSL synthesis starts in the endoplasmic reticulum (ER) where a sphingoid base is condensed with anacyl-CoA, to generate Ceramide (Cer) [102,103] (Figure 1). In the ER, Cer can be galactosylated to produce galactosylceramide (GalCer) [104]. GalCer is, then, transported to the Golgi complexwhere it can be sulphated to produce sulphogalactolipids, or sialylated to produce the GM4 ganglioside . Alternatively, Cer can be conveyed to the Golgi complex via transport vesicles or by the ceramide-transfer protein CERT [105]. CERT transports Cer to the trans-Golgi network (TGN) where it is primarily used for the synthesis of sphingomyelin (SM) (Figure 1). On the contrary, Cer transported to Golgi by vesicular transport is converted to glucosylceramide (GlcCer). GlcCer is synthesized by the addition of a glucose residue to Cer on the cytosolic leaflet ofcis-Golgi membranes and GlcCer is further glycosylated by the activity of glycosyltransferases distributed along Golgi cisternae, resulting in more than 300 species of GSLs. These enzymes transfer a specific carbohydrate from the appropriate activated sugar nucleotide (e.g., UDP-Galactose, CMP-sialic acid, UDP-Fucose, etc.) to the non-reducing end of the growing carbohydrate chain linked to GlcCer
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