FAQ: What is the difference between N-glycans, O-glycans, O-GlcNAc and proteoglycans (also called glycosaminoglycans, or GAGs)?

N-glycans are attached to the amino side chain of an asparagine residue, O-glycans are attached to the side chain of serine or threonine residues, both are typically found in proteins processed through the ER and Golgi. O-GlcNAc refers to a single N-Acetylglucosamine (GlcNAc) residue, attached to serine and threonine in certain nuclear and cytoplasmic proteins. Proteoglycans are found in the extracellular matrix, and are proteins with very large glycan chains such as Heparin or Heparan sulfate. More information can be found in this article: Biosynthesis of Glycans in Eukaryote