Glycosylation is one of the most abundant of all protein post-translational modifications (PTMs). It results from the addition of sugar residues to protein sidechains to form a glycoprotein. Mammalian glycoprotein oligosaccharides are commonly built from a limited number of monosaccharides but their structural diversity is vast, mainly because they often form complex branching patterns. Glycosylation is not template-driven and is currently impossible to predict.
Glycosylation plays an important role in many specific biological functions, including immune defense, fertilization, viral replication, parasitic infection, cell growth, inflammation, and cell-cell adhesion. For pharmaceutical glycoproteins, glycosylation affects stability of protein conformation, clearance rate, protection from proteolysis, and improves protein solubility.
A protein´s pattern of glycosylation depends on many factors, including the type of cell producing the glycoprotein, nutrient concentrations, pH, cell density, and age. Different cell lines and different fermentation conditions can produce significantly different glycosylation patterns. Since different glycoforms have the potential to have different biological properties, the ability to monitor and control glycosylation during production is critical to the quality of a biopharmaceutical molecule.