Proteomic analysis of glycosylation: structural determination of N- and O-linked glycans by mass spectrometry

This review summarizes the methods, mainly based on mass spectrometry, for the structural determination of N- and O-linked carbohydrates that are post-translationally attached to a large number of proteins and which play a key role in determining the function and biophysical properties of these compounds. Analysis of these carbohydrates has proved difficult in the past due to their structural complexity. However, modern analytical methods such as mass spectrometry have the ability to elucidate most structural details at the concentration levels required for proteomics. This review describes methods for direct examination of glycoproteins by mass spectrometry, the release of N- and O-linked glycans from glycoproteins separated in sodium dodecyl sulfate polyacrylamide electrophoresis gels, and the analysis of these compounds by techniques such as matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry. Matrix-assisted laser desorption/ionization mass spectrometry provides the most rapid method for comparing glycan profiles and is probably most appropriate for clinical studies. One of the most promising techniques for determining the structures of N-glycans in proteomic studies is negative ion fragmentation of electrosprayed ions. This technique combines high throughput with ease of structural interpretation and provides structural details that are difficult to obtain by classical methods.