N-glycosylation site

It has been known for a long time [1] that potential N-glycosylation sites are specific to the consensus sequence Asn-Xaa-Ser/Thr. It must be noted that the presence of the consensus tripeptide is not sufficient to conclude that an asparagine residue is glycosylated, due to the fact that the folding of the protein plays an important role in the regulation of N-glycosylation [2]. It has been shown [3] that the presence of proline between Asn and Ser/Thr will inhibit N-glycosylation; this has been confirmed by a recent [4] statistical analysis of glycosylation sites, which also shows that about 50% of the sites that have a proline C-terminal to Ser/Thr are not glycosylated.

It must also be noted that there are a few reported cases of glycosylation sites with the pattern Asn-Xaa-Cys; an experimentally demonstrated occurrence of such a non-standard site is found in the plasma protein C [5].