Decoding Extracellular Protein Glycosylation in Human Health and Disease

Protein glycosylation, the covalent attachment of carbohydrate, or glycan, structures onto the protein backbone, is one of the most complex and heterogeneous post-translational modifications (PTMs). Extracellular protein glycosylation, in particular N- and mucin-type O-glycosylation, plays pivotal roles in a number of biophysical and biochemical processes, such as protein folding and stability, cell adhesion, signaling, and protection. As such, aberrant glycosylation is implicated in a variety of diseases, including cancer. However, the nontemplated nature and structural heterogeneity of protein glycosylation hinder glycoprotein characterization with traditional methods. Recent advances in analytical techniques have improved capabilities for decoding glycan complexity, a promising step toward understanding the role of glycosylation in human health and disease. In this review, we highlight key and emerging techniques to study protein glycosylation, and we emphasize how these techniques have improved our understanding of glycosylation in a biologically relevant context.