High-sensitivity analysis of sialyl-oligosaccharide glycosylation sites in glycoproteins by miniaturized tryptic digestion and microcolumn liquid chromatography

Capillary biomolecular separations

This article summarizes the recent advances in microcolumn separations of biopolymers. Microcolumn liquid chromatography is primarily emphasized for its role as a micropreparative and fractionation tool, whereas high-performance capillary electrophoresis is demonstrated as a highly efficient technique for final analyses. Following a brief discussion of new trends in instrumentation, the recent applications of capillary techniques to proteins, DNA and glycoconjugates are reviewed.

Application of a sensitive HPLC-based fluorometric assay to determine the sialic acid content of human gonadotropin isoforms

The human pituitary gonadotropins, follitropin (hFSH) and lutropin (hLH) are glycoproteins which are microheterogeneous in terms of their charge and molecular size, as well as their in vitro and in vivo bioactivities. The aim of this study was to determine the contribution of variations in sialic acid (N-acetyl neuraminic acid) content to the structural heterogeneity of these glycoproteins. Sialic acid (Neu5Ac) was released by partial acid hydrolysis (0.1 M TFA, 80 degrees C, 1 h) and derivatised with the fluorescent label DMB (1,2-diamino-4,5-methylenedioxybenzene) in conjunction with an internal standard (N-glycoyl-neuraminic acid). The derivatives were then separated by reversed-phase HPLC. This method allowed quantitation of the sialic acid content over a range of 5-100 pmol with between assay variation of < 6% for sialic acid released from approximately 100 ng (3 pmol) of hFSH or hLH. Comparison of the sialic acid contents of standard sialylated glycoproteins by either DMB-derivatisation or high-performance anion-exchange chromatography with pulsed amperometric detection yielded similar results, confirming the reliability of the fluorescence detection method. The sialic acid contents of 9 hFSH isoforms varied between 1.5-13.7 mol Neu5AC/mol FSH, whilst a range of 1.1-9.1 mol Neu5AC/mol LH was observed for 12 hLH isoforms. The sialic acid content of the hFSH isoforms was also observed to be related to the hormonal specific activity in a radioreceptor assay, confirming that alterations in the carbohydrate structure can influence the FSH-receptor interaction. In contrast, the sialic acid content of the hLH isoforms was found to be not related to specific activity at the receptor level.

Analysis of protein modifications: recent advances in detection, characterization and mapping

The past year has seen several contributions, both in methods for determining and characterizing chemical modifications of proteins and in related technologies used to map peptides. These contributions mainly involve improvements in capillary zone electrophoresis and in various applications of mass spectrometry.

High-performance capillary electrophoresis of glycoconjugates

Capillary electrophoresis (CE) has recently emerged as a highly promising technique for the analysis and structural study of glycoconjugates. This article reviews the current status of CE and its potential in glycobiology. The separation media suitable for the analysis of monosaccharides, oligosaccharides and very large carbohydrate-based biomolecules are discussed. The detection aspects emphasize chemical derivatization approaches to tagging the glycoconjugates of interest for enhanced response in absorption and fluorescence spectroscopy.