Free oligosaccharides in serum

Glycans are sugars/sugar chains that are usually linked to proteins or lipids. The attachment of glycans often results in alterations of physicochemical/physiological properties of the carrier molecules, e.g., glycosylation of proteins can modulate their fate, intracellular localization, or interaction with cells/other proteins. On the other hand, unconjugated N-glycans (free N-glycans; FNGs) have been identified in the cytosol of eukaryotic cells. The processing pathway of intracellular FNGs has been clarified in recent years, but their biological functions remain unclear. […] This mini-review summarizes current knowledge about the structures and formation mechanisms of free oligosaccharides in serum, and suggests their possible biological functions.