N-linked glycosylation.

In addition to their central role in energy metabolism and the core pathways of biosynthesis, carbohydrates can be seen performing a multitude of other functions in living systems from the structural roles of cellulose, chitin and peptidoglycan to the important role for carbohydrates we see in N- and O-linked glycosylation in the post-translational modification of many proteins.Formed in the lumen of the endoplasmic reticulum by modification of proteins following synthesis, glycoproteins often play an important informational roll in the process of infection, such as the recognition by a virus for its host by cell surface glycoproteins. Another example of an antigen-antibody interaction mediated by glycoproteins is blood-type compatibility. Glycoproteins on red blood cells determine blood type.