Table 1. General features of different glycosylation types.

Glycosylation Type	Glycosylation Sequences Motifs	Glycosylation Acceptor Site	Organism	Reference
N-glycosylation	In eukaryotes, glycan molecules are attached to the asparagine residue from sequons: Asn-x-Ser and Asn-x-Thr, or in some rare cases in Asn-x-Cys where x is not a proline residue. In prokaryotes, the sequon is extended to Asp/Glu-z-Asn-x-Ser and Asp/Glu-z-Asn-x-Thr, where x and z are not proline residues.	Nitrogen atom from the amide group in the asparagine residue	Eukaryotes and prokaryotes	[30], [31]
O-glycosylation	No specific sequence motifs have been defined. Sugars are attached to serine and threonine residues usually found in a beta conformation and in close vicinity to proline residues.	Oxygen atom from the hydroxyl group in serine or threonine residues	Eukaryotes and prokaryotes	[32]–[34]
C-glycosylation	Carbohydrates are attached to the first tryptophan residue from the following motifs: Trp-x-x-Trp, Trp-x-x-Phe, Trp-x-x-Tyr, and Trp-x-x-Cys. Any amino acid could be placed at the x position, although small and/or polar residues are preferred, such as alanine, glycine, serine, and threonine.	Carbon atom (C2) from the indole group in the tryptophan residue	Eukaryotes except yeast	[35]–[39]
GPI anchor	A specific C-terminal signal sequence is recognized and cleaved, creating a new C-terminal protein end (ω-site). The GPI molecule is added to the ω-site. No consensus sequence for ω-site localization has been described. Typical residues in ω-site include: cysteine, aspartic acid, glycine, asparagine, and serine.	Carbon atom from the C-terminal carbonyl group at the ω-site	Eukaryotes and a reduced subset of archaea	[40]–[42]

GPI, glycosylphosphatidylinositol.