The unexpected, non-enzymatic S-glycosylation of cysteine residues in various proteins by per-O-acetylated monosaccharides is described. This artificial S-glycosylation greatly compromises the specificity and validity of metabolic glycan labeling in living cells by per-O-acetylated azido and alkynyl sugars, which has been overlooked in the field for decades. It is demonstrated that the use of unacetylated unnatural sugars can avoid the artifact formation and a corrected list of O-GlcNAcylated proteins and O-GlcNAc sites in HeLa cells has been assembled by using N-azidoacetylgalactosamine (GalNAz).
Keywords: O-GlcNAc; S-glycosylation; chemoproteomics; labeling; unnatural monosaccharides.
© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.