Structural characterization of site-specific N-glycosylation of recombinant human factor VIII by reversed-phase high performance liquid chromatography electrospray ionization mass spectrometry

The present study addresses the site occupancy and the site-specific carbohydrate microheterogeneity of N-linked oligosaccharides in recombinant human factor VIII, expressed in Chinese hamster ovary cells. The four factor VIIIa polypeptides, formed upon incubation with human thrombin, were isolated and separately subject to proteolysis with trypsin. These tryptic digests were analyzed by reversed-phase high-performance liquid chromatography/electrospray ionization mass spectrometry. Selected ion monitoring of diagnostic carbohydrate ions was utilized to identify glycopeptide-containing chromatographic peaks. Oligomannose and complex carbohydrates were detected at the glycosylation sites of the 50 and 73 kDa polypeptides, while all the oligosaccharides identified on the B-domain were complex-type structures. Only the 43 kDa polypeptide was found nonglycosylated. These studies established a biantennary core-fucosylated carbohydrate as the major substituent, consistent with the conclusions of the analyses on the entire N-linked carbohydrate pool (Kumar, H. P. M.; Hague, C.; Haley, T.; Starr, C. M.; Besman, M. J.; Lundblad, R.; Baker, D. Biotechnol. Appl. Biochem. 1996, 24, 207-216.). In addition, this mass spectrometric investigation revealed the presence of a complex nonfucosylated oligosaccharide not reported previously for this glycoprotein.