Structural Analysis of Carbohydrate Chains of Native and Recombinant-DNA Glycoproteins. In: Crommelin DJA, Schellekens H, editors. From Clone to Clinic. Dordrecht: Springer Netherlands; 1990. pp. 295-304. [DOI: 10.1007/978-94-011-3780-5_37]

The complexity of glycoprotein-derived glycans

A brief review is presented of our studies on the structure of glycoprotein-derived glycans. The emphasis is on the introduction of high-resolution 1H-NMR spectroscopy for the unambiguous determination of primary structures. For this purpose, we developed the structural reporter group concept. Structural reporters are defined as unique markers of structural elements in the NMR spectra. Application of this concept led to the discovery of numerous new structures. Furthermore, a number of structures presented in the literature could be corrected. The results are relevant for insight in the various steps in glycan metabolism in health and disease, for the function and mode of action of glycans in vivo and for the interpretation of structural information obtained through other techniques. The strength of the approach is further shown for several highly complex glycoproteins, carrying very heterogeneous and complicated glycans.

High-level expression of biologically active glycoprotein hormones in Pichia pastoris strains--selection of strain GS115, and not X-33, for the production of biologically active N-glycosylated 15N-labeled phCG

The methylotrophic yeast Pichia pastoris is widely used for the production of recombinant glycoproteins. With the aim to generate biologically active ¹⁵N-labeled glycohormones for conformational studies focused on the unravelling of the NMR structures in solution, the P. pastoris strains GS115 and X-33 were explored for the expression of human chorionic gonadotropin (phCG) and human follicle-stimulating hormone (phFSH). In agreement with recent investigations on the N-glycosylation of phCG, produced in P. pastoris GS115, using ammonia/glycerol-methanol as nitrogen/carbon sources, the N-glycosylation pattern of phCG, synthesized using NH₄Cl/glucose–glycerol–methanol, comprised neutral and charged, phosphorylated high-mannose-type N-glycans (Man_8–15GlcNAc₂). However, the changed culturing protocol led to much higher amounts of glycoprotein material, which is of importance for an economical realistic approach of the aimed NMR research. In the context of these studies, attention was also paid to the site specific N-glycosylation in phCG produced in P. pastoris GS115. In contrast to the rather simple N-glycosylation pattern of phCG expressed in the GS115 strain, phCG and phFSH expressed in the X-33 strain revealed, besides neutral high-mannose-type N-glycans, also high concentrations of neutral hypermannose-type N-glycans (Man_up-to-30GlcNAc₂). The latter finding made the X-33 strain not very suitable for generating ¹⁵N-labeled material. Therefore, ¹⁵N-phCG was expressed in the GS115 strain using the new optimized protocol. The ¹⁵N-enrichment was evaluated by ¹⁵N-HSQC NMR spectroscopy and GLC-EI/MS. Circular dichroism studies indicated that ¹⁵N-phCG/GS115 had the same folding as urinary hCG. Furthermore, ¹⁵N-phCG/GS115 was found to be similar to the unlabeled protein in every respect as judged by radioimmunoassay, radioreceptor assays, and in vitro bioassays.

Characterization of the N-linked oligosaccharides from human chorionic gonadotropin expressed in the methylotrophic yeast Pichia pastoris

Human chorionic gonadotropin (hCG) is a heterodimeric, placental glycoprotein hormone involved in the maintenance of the corpus luteum during the first trimester of pregnancy. Biologically active hCG has been successfully expressed in the yeast Pichia pastoris (phCG). In the context of structural studies and therapeutic applications of phCG, detailed information about its glycosylation pattern is a prerequisite. To this end N-glycans were released with peptide-N(4)-(N-acetyl-beta-glucosaminyl)asparagine amidase F and fractionated via anion-exchange chromatography (Resource Q) yielding both neutral (80%) and charged, phosphate-containing (20%) high-mannose-type structures. Subfractionations were carried out via normal phase (Lichrosorb-NH(2)) and high-pH anion-exchange (CarboPac PA-1) chromatography. Structural analyses of the released N-glycans were carried out by using HPLC profiling of fluorescent 2-aminobenzamide derivatives, MALDI-TOF mass spectrometry, and 500-MHz(1)H-NMR spectroscopy. Detailed neutral oligosaccharide structures, in the range of Man(8)GlcNAc(2) to Man(11)GlcNAc(2) including molecular isomers, could be established, and structures up to Man(15)GlcNAc(2) were indicated. Phosphate-containing oligosaccharides ranged from Man(9)PGlcNAc(2) to Man(13)PGlcNAc(2). Mannosyl O-glycans were not detected. Profiling studies carried out on different production batches showed that the oligosaccharide structures are similar, but their relative amounts varied with the culturing media.

The major N-linked carbohydrate chains from human urokinase. The occurrence of 4-O-sulfated, (alpha 2-6)-sialylated or (alpha 1-3)-fucosylated N-acetylgalactosamine(beta 1-4)-N-acetylglucosamine elements

The primary structure of the major N-linked carbohydrate chains attached to Asn302 of urinary-type plasminogen activator (urokinase) have been determined. Urokinase was completely deglycosylated with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F from Flavobacterium meningosepticum. Released oligosaccharides were separated from the remaining protein using gel-permeation chromatography on Bio-Gel P-100, and then on Bio-Gel P-6. Fractionation of the oligosaccharides was achieved by a combination of FPLC anion-exchange chromatography on Mono Q HR 5/5 and amine-adsorption HPLC on LiChrospher 100-NH2. Analysis by 1H-NMR spectroscopy demonstrated that the collection of N-glycans comprises di-, tri-, and tri'-antennary structures. The glycans contain predominantly GalNAc beta 1-4GlcNAc beta instead of Gal beta 1-4GlcNAc beta elements. The GalNAc residue is mainly sulfated at O4, or to a lesser extent it bears N-acetylneuraminic acid at O6; alternatively the GlcNAc residue can be fucosylated at O3. The major component, which accounts for more than 30 mol/100 mol of the total oligosaccharide pool, consists of an (alpha 1-6)-fucosylated diantennary N-linked carbohydrate chain with (SO4-)-4GalNAc beta 1-4GlcNAc beta 1-2 antennae.

Primary structure of N-linked carbohydrate chains of a human chimeric plasminogen activator K2tu-PA expressed in Chinese hamster ovary cells

A recombinant human plasminogen activator hybrid variant K2tu-PA, expressed in Chinese hamster ovary cells, is partially glycosylated at Asn12 (A chain, kringle-2 domain) and completely glycosylated at Asn247 (B chain, protease domain). After release of the N-linked carbohydrate chains by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F, the oligosaccharides were separated from the protein by gel permeation chromatography, then fractionated by FPLC on Mono Q, followed by HPLC on Lichrosorb-NH2, and analysed by 500-MHz 1H-NMR spectroscopy. The following types of carbohydrates occur: monosialylated diantennary (8%), disialylated diantennary (45%), disialylated tri- and tri'-antennary (1%), trisialylated tri- and tri'-antennary (28%), and tetrasialylated tetra-antennary (18%) structures, all having fucose in alpha(1-6)-linkage at the Asn-bound N-acetylglucosamine. Sialic acid occurred exclusively in alpha(2-3)-linkage to galactose, and consisted of N-acetylneuraminic acid (94%), N-glycolylneuraminic acid (3%), and N-acetyl-9-O-acetylneuraminic acid (3%). In addition, glycopeptide fragments corresponding with the A or B chain of K2tu-PA were analysed. The oligosaccharides attached to Asn12 are less processed than those attached to Asn247. Comparison of the glycosylation pattern of K2tu-PA with that of tissue-type plasminogen activator from different biological sources showed significant differences. Profiling studies on different K2tu-PA production batches demonstrated that the structures of N-linked oligosaccharides were identical, but that relative amounts vary with the applied isolation procedure of the chimeric glycoprotein.

The carbohydrate chains of the beta subunit of human chorionic gonadotropin produced by the choriocarcinoma cell line BeWo. Novel O-linked and novel bisecting-GlcNAc-containing N-linked carbohydrates

The N-linked carbohydrate chains of the beta subunit of human chorionic gonadotropin (hCG-beta) isolated from the culture fluid of the choriocarcinoma cell line BeWo were released enzymatically by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Subsequently, the O-linked oligosaccharides were split off from the N-deglycosylated protein by mild alkaline borohydride treatment. The carbohydrate chains were purified in their intact sialylated forms by FPLC anion-exchange chromatography on Mono Q, HPLC on Lichrosorb-NH2, and high-pH anion-exchange chromatography on CarboPac PA1. 1H-NMR spectroscopic analysis of the major fractions demonstrates the occurrence of the following sialylated diantennary and triantennary N-linked oligosaccharides. Residues not written in bold letters are variably present. [formula: see text] The incidence of triantennary carbohydrate chains is much higher than in normal urinary hCG-beta (26% vs 2%). The same holds for the alpha 1-6-fucosylation of the asparagine-bound GlcNAc (95% vs 42%). The presence of a bisecting GlcNAc and the occurrence of alpha 2-6-linked Neu5Ac in the most abundant N-glycans, are new features for hCG-beta. The major O-linked carbohydrate chains identified are the tetrasaccharide Neu5Ac alpha 2-3Gal beta 1-3(Neu5Ac alpha 2-6)GalNAc-ol and the hexasaccharide Neu5Ac alpha 2-3Gal beta 1-4GlcNAc beta 1-6(Neu5Ac alpha 2-3Gal beta 1-3)GalNAc-ol, both also found in normal urinary hCG. In addition, two novel O-glycans were characterized: [formula: see text]