Glycosylated protein biopharmaceuticals

Characterization of carbohydrates in glycoproteins has become an important task in the field of biotechnology, since a number of protein biopharmaceuticals are glycosylated. To gain detailed structural information, it would be advantageous to have a routine profiling method that can provide suitable samples for further analysis. 

Physcomitrella is a well-established plant system that, since the 1960s, has been cultivated under axenic conditions in many laboratories. It can be cultivated in liquid cultures, and such photobioreactors are scaleable. Transgenic moss strains show high genetic stability. Different biopharmaceuticals, including human growth factor, antibodies and non-glycosylated proteins such as HSA were successfully expressed and secreted into the medium. 

Many polypeptides undergo covalent modification after (or sometimes during) their ribosomal assembly. The most commonly observed such PTMs are listed in Table 2.7. Such modifications generally influence either the biological activity or the structural stability of the polypeptide. The majority of therapeutic proteins bear some form of PTM. Although glycosylation represents the most common such modification, additional PTMs important in a biopharmaceutical context include carboxylation, hydroxylation, sulfation and amidation these PTMs are now considered further. 

Technical advances facilitating genetic manipulation of animal cells now allow routine production of therapeutic proteins in such systems. The major advantage of these systems is their ability to carry out post-translational modification of the protein product. As a result, many biopharmaceuticals that are naturally glycosylated are now produced in animal cell lines. CHO and BHK cells have become particularly popular in this regard. 

This technique is also utilized in the biopharmaceutical industry to determine product homogeneity. Homogeneity is best indicated by the appearance in the gel of a single protein band, exhibiting the predicted pi value. Interpretation of the meaning of multiple bands, however, is less straightforward, particularly if the protein is glycosylated (the bands can also be stained for... 

This chapter describes some of the most important and well-studied forms of post-translational modifications of proteins, which have been associated with the production of glycoproteins as biopharmaceuticals from mammalian cell culture systems. Most attention is given to glycosylation because of its general importance for the activity of all these... 

With product yield at its near maximum, the BEVS community is currently focusing on the improvement of product quality by humanizing insect cell glycosylation patterns. The unique combination of transient expression implementation, high-yield protein production capacity and the prospect of human glycoprofiles in insect cultures indicates a bright future for BEVS technology in the production of biopharmaceuticals [4, 6, 7]. 

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