The mapping by high-pH anion-exchange chromatography with pulsed amperometric detection and capillary electrophoresis of the carbohydrate moieties of human plasma alpha 1-acid glycoprotein.
The reducing oligosaccharides released from alpha 1-acid glycoprotein (AGP) by conventional hydrazinolysis have been analyzed by two different mapping techniques, using high-pH anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) and capillary electrophoresis (CE) with uv detection at 190 nm. The CE measurements proved about 4000 times more sensitive than the measurements by HPAE-PAD. The N-glycan pool was fractionated by Mono Q anion-exchange chromatography, and individual fractions so obtained were desialylated using Vibrio cholerae neuraminidase. The resulting asialo-N-glycans were further analyzed by HPAE-PAD, revealing 2 major, 4 intermediate, and 4 small peaks and at least 3 spikes, which counted for at least 13 different asialo-N-glycans. The carbohydrate structures were tentatively assigned by comparison of the Mono Q-separated N-glycans with the known AGP carbohydrate structures and known structures contained in a mapping database that allows structural assignment of N-glycans by mere comparison of retention times. In addition to the hitherto known AGP carbohydrate structures, we have tentatively identified a number of sulfated N-glycans that are currently being analyzed in more detail. We have also compared the glycan pools recovered from AGP using hydrazinolysis and glycopeptidase F (PNGase F). Approximately 40 distinct peaks could be detected in the hydrazinolysis-derived N-glycan pool by either technique (HPAE-PAD and CE), while about 30 distinct peaks were detected in the N-glycan pool derived by PNGase F digestion of the tryptic AGP digest of the same batch of AGP. These differences were attributed to an increased desialylation (approximately 3 mol%) during hydrazinolysis, based on the detection by HPAE-PAD and CE of free sialic acid and monosialylated oligosaccharides in the glycan pool derived by conventional hydrazinolysis. The integrity of the N-glycans' chitobiose core was examined by 500-MHz 1H NMR spectoscopy. The hydrazinolysis procedure could be optimized such that the hydrazinolysis-derived N-glycan pool was chromatographically essentially identical to the PNGase F-derived N-glycan pool. Hydrazinolysis proved best, with practically no loss of N-acetlylneuraminic acid and the closest resemblance to the PNGase F-derived N-glycan pool, using an automated apparatus. Notably, it was recognized that, in our hands, PNGase F digestion in the presence of sodium dodecyl sulfate resulted in partial desialylation of the liberated N-glycans.
Hermentin
P
P
Research Laboratories of Behringwerke AG, Marburg, Germany.
Witzel
R
R
Doenges
R
R
Bauer
R
R
Haupt
H
H
Patel
T
T
Parekh
R B
RB
Brazel
D
D
D002197:Capillary Action; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000032:analysis; D002852:Chromatography, Ion Exchange / Q000379:methods; D004586:Electrophoresis / Q000379:methods; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry* / Q000302:isolation & purification; D009961:Orosomucoid / Q000737:chemistry*; D011199:Potentiometry / Q000379:methods
D002241:Carbohydrates; D009844:Oligosaccharides; D009961:Orosomucoid