Glycoproteins constitute the class of glycoconjugates in which glycans (carbohydrate moieties) are covalently associated with the proteins, usually through the N atom of asparagines (N-glycans) or the O atom of serine/threonine (O-glycans). Glycosylation of proteins represents one of the most common and important post-translational phenomenons. Most proteins in an organism are glycoproteins. Glycans in glycoproteins are known to play several biological roles. Some examples are the protection of the protein from proteolysis attack; cell-cell interactions through lectins; association with enzymes, bacteria, and viruses; and maintaining protein conformation in a biologically active form.