analysis of protein glycosylation by mass spectrometry Glycosylation, the attachment of sugar moieties to proteins, is a post-translational modification (PTM) that provides greater proteomic diversity than other PTMs. Glycosylation is critical for a wide range of biological processes, including the attachment of cell to the extracellular matrix and intracellular protein-ligand interactions. This PTM is characterized by various glycosidic linkages, including N-, O- and C-linked glycosylation, glypiation (GPI anchor attachment), and phosphoglycosylation, etc.