Chemical biology of glycoproteins: From chemical synthesis to biological impact.

Recent advances have demonstrated the feasibility and robustness of chemical synthesis for the production of homogeneously glycosylated protein forms (glycoforms). By taking advantage of the unmatchable flexibility and precision provided by chemical synthesis, the quantitative effects of glycosylation were obtained using chemical glycobiology approaches. These findings greatly advanced our fundamental knowledge of glycosylation.

O-GalNAcylation of RANTES Improves Its Properties as a Human Immunodeficiency Virus Type 1 Entry Inhibitor.

Many human proteins have the potential to be developed as therapeutic agents. However, side effects caused by direct administration of natural proteins have significantly slowed expansion of protein therapeutics into the clinic. Post-translational modifications (PTMs) can improve protein properties, but because of significant knowledge gaps, we are considerably limited in our ability to apply PTMs to generate better protein therapeutics.

Chemically Precise Glycoengineering Improves Human Insulin.

Diabetes is a leading cause of death worldwide and results in over 3 million annual deaths. While insulin manages the disease well, many patients fail to comply with injection schedules, and despite significant investment, a more convenient oral formulation of insulin is still unavailable. Studies suggest that glycosylation may stabilize peptides for oral delivery, but the demanding production of homogeneously glycosylated peptides has hampered transition into the clinic.

Quantitative Effects of O-Linked Glycans on Protein Folding.

Protein O-glycosylation is a diverse, common, and important post-translational modification of both proteins inside the cell and those that are secreted or membrane-bound. Much work has shown that O-glycosylation can alter the structure, function, and physical properties of the proteins to which it is attached. One gap remaining in our understanding of O-glycoproteins is how O-glycans might affect the folding of proteins.

Structural Insight into the Stabilizing Effect of O-Glycosylation.

Protein glycosylation has been shown to have a variety of site-specific and glycan-specific effects, but so far, the molecular logic that leads to such observations has been elusive. Understanding the structural changes that occur and being able to correlate those with the physical properties of the glycopeptide are valuable steps toward being able to predict how specific glycosylation patterns will affect the stability of glycoproteins. By systematically comparing the structural features of the O-glycosylated carbohydrate-binding module of a Trichoderma reesei-derived Family 7 cellobiohydrolase, we were able to develop a better understanding of the influence of O-glycan structure on the molecule's physical stability.