The ALG10 locus of Saccharomyces cerevisiae encodes the alpha-1,2 glucosyltransferase of the endoplasmic reticulum: the terminal glucose of the lipid-linked oligosaccharide is required for efficient N-linked glycosylation |
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Authors: | Burda P; Aebi M |
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Institution: | Mikrobiologisches Institut, ETH Zurich, Switzerland. |
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Abstract: | The biosynthesis of the lipid-linked oligosaccharide substrate for N-
linked protein glycosylation follows a highly conserved pathway at the
membrane of the endoplasmic reticulum. Based on the synthetic growth defect
in combination with a reduced oligosaccharyltransferase activity (wbp1), we
have identified alg10 mutant strains which accumulate lipid- linked
Glc2Man9GlcNAc2. We cloned the corresponding wild-type gene and show in a
novel in vitro assay that Alg10p is a dolichyl-phosphoglucose- dependent
glucosyltransferase which adds the terminal alpha-1,2 glucose to the
lipid-linked Glc2Man9GlcNAc2 oligosaccharide. Hypoglycosylation of secreted
proteins in alg10 deletion strains demonstrates that the terminal
alpha-1,2-linked glucose residue is a key element in substrate recognition
by the oligosaccharyltransferase. This ensures that primarily completely
assembled oligosaccharide is transferred to protein.
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