a protein with sugars attached. ~1/2 of all proteins have at least one glycan (sugar chain) & some glycoproteins are up to 60% carb by mass. Glycoproteins are often found in the outer leaflet of the plasma membrane, facing the cellular exterior, or secreted into the extracellular matrix. The sugar chains can be O-linked or N-linked. O-glycosylation is where a sugar chain gets added through the -OH group of a Serine (Ser) or Threonine (Thr) protein letter (or a hydroxylated lysine or proline). N-glycosylation is where a sugar chain gets added through the amine group of an Asparagine (Asp) letter.
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