Structural characterization of N-glycopeptides by matrix-dependent selective fragmentation of MALDI-TOF/TOF tandem mass spectrometry.

The matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS technique described to date has proven to be a convenient and rapid method for identification and characterizations of proteins. However, the general MALDI-TOF MS analysis of complex carbohydrates and glycopeptides still entails special consideration of ionization and the fragmentation characteristics of labile carbohydrate moieties. In this study, an efficient and practical method we termed the matrix-dependent selective fragmentation (MDSF) technique of MALDI-TOF/TOF MS, which allows highly sensitive and reliable fragmentation of oligosaccharides and N-glycopeptides. Results from application of the MDSF technique to TOF/TOF MS analysis demonstrated that in comparison to the conventional postsource decay up to 170 times more sensitive product ion peaks could be obtained. It was also suggested that MDSF generates desired structural information based on the controlled cleavage of the singly charged precursor ion with different electronic excited states made by this method. Ideal product ion peaks observed by MDSF in TOF/TOF MS facilitated structural characterization of complex oligosaccharide derivatives including unstable Neu5Ac and Fuc residues and N-glycopeptides.