ABSTRACT
Glycosylation of proteins is one of the most common and important post-translational modifications found in eukaryotic secretory proteins. Carbohydrate moieties of glycoconjugates long were believed to carry no information and be devoid of biological function. Methods for analyzing carbohydrates were not available or at least labor-intensive. It has become clear only in recent years that basic glycosylation processes are both compli cated and conserved during evolution, and that the type and extent of 7V-glycosylation often contributes to the physicochemical and recognition properties of glycoproteins [1,2]. Furthermore, it is now realized that the biological activity of glycoprotein hormones frequently depends on the attached N-linked oligosaccharides [3,4]. In recent years, the role of Nglycosylation in Chinese hamster ovary (CHO)-expressed human proteins has been studied extensively [5,6]. Some functional aspects of oligosaccha rides in glycoproteins now appear to be universal (e.g., solubility [7] and circulatory lifetime [8,9]), but most other possible roles such as facilitating secretion, affecting biological activity, or increasing stability have to be investigated for each protein. CHO cells are the most commonly used euk aryotic cells for production of human proteins in biotechnology. They are adaptable for growth in suspension —which is inevitable for large scale production processes — and are robust to culture. Combined with the selec tion marker dihydrofolate reductase (DHFR), they represent a reliable ex pression system. Furthermore, they glycosylate proteins similarly to human cells. Although A/-glycosylation is mainly governed by the type of host cell
and the primary structure of the expressed glycoprotein, environmental factors also influence glycosylation [10-14], Alterations in oligosaccharide structures occur either by affecting synthesis or by changing glycosidase activity after secretion [15,16], Because changing the glycosylation pattern may have important consequences in glycoprotein pharmaceuticals, carbo hydrate analysis is of utmost importance in product characterization to ensure consistent product quality.
