Structural analysis of the sialylated N- and O-linked carbohydrate chains of recombinant human erythropoietin expressed in Chinese hamster ovary cells. Sialylation patterns and branch location of dimeric N-acetyllactosamine units.
The N-linked carbohydrate chains of recombinant human erythropoietin expressed in CHO cells were quantitatively released with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F, separated from the remaining O-glycoprotein by gel-permeation chromatography, and subsequently fractionated via FPLC on Mono Q, HPLC on Lichrosorb-NH2 and high-pH anion-exchange chromatography on CarboPac PA1. The purified sialylated oligosaccharides were analyzed by one-dimensional and two-dimensional 500-MHz 1H-NMR spectroscopy. When necessary, oligosaccharides were treated with endo-beta-galactosidase (and N-acetyl-beta-glucosaminidase) followed by 1H-NMR analysis of the incubation products, to obtain additional structural information. Di-, tri-, tri'- and tetraantennary N-acetyllactosamine-type oligosaccharides occur which can be completely (major) or partially (minor) sialylated. Three different types of alpha 2-3-linked sialic acids are present, namely, N-acetylneuraminic acid (95%), N-glycolylneuraminic acid (2%) and N-acetyl-9-O-acetylneuraminic acid (3%). In the case of partial sialylation, a non-random distribution of the sialic acids over the branches is observed. One or two extra N-acetyllactosamine units, being exclusively located in the branches attached to the alpha 1-6-linked Man residue, can be present in completely or partially sialylated di-, tri'-, and tetraantennary oligosaccharides. Tetraantennary oligosaccharides with N-acetyllactosamine repeats could be digested quantitatively with endo-beta-galactosidase from Bacteroides fragilis, whereas under the same conditions tri' antennary oligosaccharides hardly reacted (< 15%). Using endo-beta-galactosidase from Escherichia freundii, these tri'antennary oligosaccharides could be digested more extensively (> 75%). The O-linked carbohydrate chains were released from the O-glycoprotein by alkaline borohydride treatment, and purified via FPLC on Mono Q and HPLC on Lichrosorb-NH2. Two O-glycans were found, namely, Neu5Ac alpha 2-3Gal beta 1-3GalNAc-ol and Neu5Ac alpha 2-3Gal beta 1-3(Neu5Ac alpha 2-6)GalNAc-ol.
Hokke
C H
CH
Bijvoet Center, Department of Bio-Organic Chemistry, Utrecht University, The Netherlands.
Bergwerff
A A
AA
Van Dedem
G W
GW
Kamerling
J P
JP
Vliegenthart
J F
JF
D000606:Amino Sugars / Q000737:chemistry*; D000818:Animals; D016466:CHO Cells; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D003412:Cricetulus; D004921:Erythropoietin / Q000737:chemistry*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid; D011994:Recombinant Proteins / Q000737:chemistry; D012794:Sialic Acids / Q000737:chemistry*
D000606:Amino Sugars; D011994:Recombinant Proteins; D012794:Sialic Acids; D004921:Erythropoietin; C000458:N-acetyllactosamine; D019158:N-Acetylneuraminic Acid