Analysis of N-Glycans by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Abstract

A naturally occurring glycoprotein is made up of a population of individual glycoforms. This molecular diversity arises from variation in oligosaccharide structures at individual glycosylation sites (microheterogeneity) and variable occupation of potential glycosylation sites (variable site occupancy or macroheterogeneity). Whilst there is no analytical method capable of preparatively resolving a glycoprotein into its discrete glycoforms, several methods have been developed in recent years to characterize, to a varying extent, populations of oligosaccharides associated with glycoproteins or glycopeptides (1). Increasingly prevalent among current analytical strategies are mass spectrometric methods. Since the early 1980s, the emergence of “soft” ionization methods for biopolymer characterization by mass spectrometry (MS) such as fast atom bombardment (FAB), electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) has provided a formidable weapon in the armoury of the analytical biochemist. Typically, an FAB ion source is accompanied by a double-sector (magnetic and electrostatic) mass analyser, ESI is usually interfaced with a quadrupole analyser and MALDI generally employs simple time-of-flight (TOF) mass analysis (2, 3, 4). All techniques are capable of low picomole to femtomole sensitivity.