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J Org Chem. 2001 Sep 21;66(19):6217-28.

Substrate specificity of the glycosyl donor for oligosaccharyl transferase.

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Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.


Oligosaccharyl transferase (OT) catalyzes the co-translational transfer of a dolichol-linked tetradecasaccharide (Dol-PP-GlcNAc(2)Man(9)Glc(3), 1a) to an asparagine side chain of a nascent polypeptide inside the lumen of the endoplasmic reticulum (ER). The glycosyl acceptor requires an Asn-Xaa-Thr/Ser sequon, where Xaa can be any natural amino acid except proline, for N-linked glycosylation to occur. To address the substrate specificity of the glycosyl donor, three unnatural dolichol-linked disaccharide analogues (Dol-PP-GlcNTFA-GlcNAc 1c, Dol-PP-2DFGlc-GlcNAc 1d, and Dol-PP-GlcNAc-Glc 1e) were synthesized and evaluated as substrates or inhibitors for OT from yeast. The synthetic analogue Dol-PP-GlcNAc-Glc 1e, with substitution in the distal sugar, was found to be a substrate (K(m)(app)() = 26 microM) for OT. On the other hand, the analogues Dol-PP-GlcNTFA-GlcNAc 1c (K(i) = 154 microM) and Dol-PP-2DFGlc-GlcNAc 1d (K(i) = 252 microM), with variations in the proximal sugar, were inhibitors for OT. The dolichol-linked monosaccharide Dol-PP-GlcNAc 3 was found to be the minimum unit for glycosylation to occur.

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