Synthesis of Threefold Glycosylated Proteins using Click Chemistry and Genetically Encoded Unnatural Amino Acids
Eukaryotic proteins and in particular cell-surface proteins are frequently glycosylated, which has fueled the interest of chemist to develop new methods for the synthesis of glycosylated proteins. Protein glycosylation is essential for the proper function of the respective proteins and in the case of glycosylated protein therapeutics, such as erythropoietin, the activity of the protein strongly depends on glycosylation patterns. The synthesis and production of glycosylated proteins to either elucidate their biochemical function or to bring a new therapeutic to the market is a formidable challenge. The current most widely used methods for the production of glycosylated proteins involve over-expression of the protein in particular host systems, such as mammalian or plant cell cultures, moss cultures or tobacco plants, to name a few, that are able to make either partial or even fully glycosylated proteins. Alternatively, solid-phase synthesis of glycosylated peptides and their insertion into the protein in question by native or expressed chemical ligation has emerged as a powerful chemical strategy.