Determination of the Glycostructure in β2-Glycoprotein I by Liquid Chromatography/Electrospray Ionization Tandem Mass Spectrometry

Abstract

Over the past decade, mass spectrometry (MS) has been increasingly employed in structural analyses of glycan structures in glycoproteins. Electrospray ionization (ESI)-MS is particularly useful for this purpose. A number of reports on the direct MS analysis of digested glycopeptides have appeared recently. However, the use of MS-based techniques for the complete glycostructure of glycopeptides remains a challenging task. In this study, we report on a method for determining glycostructures in glycopeptides originating from the β2-glycoprotein I (β2-GPI). The method involves the use of liquid chromatography (LC)-ESI MS. While MS/MS spectra can provide useful information concerning glycostructures, additional MS information is needed to completely determine the composition and sequence of a glycan. This complicates the analysis, because the MS/MS data must be augmented by data from the corresponding MS spectrum involving significant in-source fragmentation of MS spectra in LC-ESI MS. In LC quadrupole-time-of-flight (Q-TOF) MS, triantennary and biantennary glycans of β2-GPI were mainly determined by combining MS and MS/MS spectral data. Finally, LC-Q-TOF MS was used to determine 24 kinds of glycopeptides at four N-glycosylation sites in β2-GPI. It also turned out that LC-Q-TOF MS was useful for the detection of glycans attached to hydrophobic peptides and other peptides that were undetectable by matrix-assisted laser desorption/ionization (MALDI)-Q-TOF MS.