Facts About Protein Glycosylation

November 01, 2023

By: Richard D. Cummings

While the N-glycosylation sequon N-X-S/T in glycoproteins of plants, fungi, and animals, is well known, there are many reports of alternative sequons for N-glycosylation in animals (1), including the sequences -N-X-C- (2-4), -N-X-V- (5,6), -N-V-E- (7), -N-X-A- (8), -N-X-G- (9), -N-N-C- (10), and the unusual glutamine rather than asparagine in the sequon -Q-G-T- (11).

While O-glycans with GalNAc α-linked to Ser/Thr are well known, the modification of GalNAc α-linked to Tyr residues is also common (12).  This modification on Tyr is resistant to the common β-elimination used for O-glycans, as that requires linkage to Ser or Thr.

C-mannosylation of Man-Trp in C-C linkages is known, but other modification of Trp can occur, as in C-glucosylation of Trp and N-mannosylation of Trp (13).  

Of the 20 canonical amino acids, 10 of them and their derivatives may be glycosylated, including Asn, Arg, Cys, Gln, HydroxyLys, HydroxyPro, Ser, Thr, Trp, and Tyr (14-19), and all but the glycosylation of HydroxyPro have been shown to occur in animal cells.  


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3.    Miletich, J. P., and Broze, G. J., Jr. (1990) Beta protein C is not glycosylated at asparagine 329. The rate of translation may influence the frequency of usage at asparagine-X-cysteine sites. The Journal of biological chemistry 265, 11397-11404
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