Lipid-linked oligosaccharides are assembled in the endoplasmic reticulum (ER) by a series of glycosyltransferases. In the lumen of the ER, four mannose residues are successively added to the Man5GlcNAc2 oligosaccharide by Alg3p, Alg9p, Algl2p and an unknown mannosyltransferase (for details, see Chapter 81). The assembly is completed via transfer of three glucose residues by the glucosyltransferases Alg6p, Alg8p, and Alg10p (Fig. 1). In contrast to the glycosyltransferases acting on the cytoplasmic face of the ER using nucleotide-activated sugars, the ER luminal glycosyltransferases require dolichol-phosphate-activated sugars. As such, the ER luminal glucosyltransferases Alg6p, Alg8p, and AlglOp require dolichol-phosphate-glucose (Dol-P-Glc) as a sugar donor (Kornfeld and Kornfeld 1985; Herscovics and Orlean 1993; Burda and Aebi 1999).
KeywordsGlucose Residue Endoplasmic Reticulum Lumen ALG6 Gene Alg6 Protein Glucosyltransferase Activity
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