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Updated: Aug 18, 2026

LERLIC-MS/MS for In-depth Characterization and Quantification of Glutamine and Asparagine Deamidation in Shotgun Proteomics
Published on: April 9, 2017
Oligosaccharyltransferase is highly specific for the hydroxy amino acid in Asn-Xaa-Thr/Ser
1Institut für Physiologische Chemie, Nussallee 11, 53115 Bonn, Germany.
Abstract:
Pig liver oligosaccharyltransferase (OST), which is involved in the en bloc transfer of the Dol-PP-linked GlcNAc(2)-Man(9)-Glc(3) precursor on to asparagine residues in the Asn-Xaa-Thr/Ser sequence, is highly stereospecific for the conformation of the 3-carbon atom in the hydroxy amino acid. Moreover, substitution of the hydroxy group by either SH as in cysteine, or NH(2) as in beta,gamma-diamino-butanoic acid as reported previously [Bause, E. et al., Biochem. J. 312 (1995) 979-985], followed by the determination of the pH optimum for enzymatic activity, indicates that neither a negative nor a positive charge in the hydroxy amino acid position is tolerated by the enzyme. Binding of the threonine beta-methyl group by OST is also specific, with serine, L-threo-beta-hydroxynorvaline and L-beta-hydroxynorleucine containing tripeptides all bound much less efficiently than the threonine peptide itself. The data are interpreted in terms of a highly stereospecific hydrophobic binding pocket for the threonine CH(3)-CH(OH) group.
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