Mass Spectrometry Approaches to Glycoproteomics

Carlito B. Lebrilla
Department of Chemistry, University of California, Davis, USA

Glycosylation is the most common form of post-translational modification. It is estimated that 50% of all proteins are glycosylated. Carbohydrates and, specifically, oligosaccharides are key in a host of cell-cell processes including recognition, fertilization, infection, division, and cancer metathesis. Despite its ubiquity and its importance, glycosylation is often missed or ignored in proteomics research. The problem lies in the difficulty of the analyses. The analyses of carbohydrates are significantly more difficult than proteins. Monosaccharide residues have numerous stereoisomers, numerous linkage arrangements, and potential for branching, which significantly complicate the analyses. The lack of rapid and sensitive analytical tools has severely hindered the progress in the area. In this lecture, new tools for the emerging area of glycomics and the analyses of oligosaccharides will be discussed. The central theme of our research is the development of mass spectrometry methods for the characterization of oligosaccharides. Mass spectrometry, specifically Fourier transform MS, provides both speed and high sensitivity. The analyses of O-linked oligosaccharides in mucins and their role in fertilization and cancer will be discussed. The methods include tandem mass spectrometry in the form of collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD). In addition, the judicious use of exoglycosidase in combination of the tandem MS methods allows the complete structural elucidation with rapidly with high sensitivity. The issue of glycosylation sites in glycoproteins containing N-linked oligosaccharides will be discussed as well as rapid methods to determine the occupation of specific sites. The action of proteases on glycoproteins the effect of steric interactions in the resulting glycopeptide products will similarly be introduced.