Fragmentation characteristics of neutral N-linked glycans using a MALDI-TOF/TOF tandem mass spectrometer

The fragmentation characteristics of native and permethylated oligosaccharides using a matrix-assisted laser desorption/ionization (MALDI) time-of-flight/time-of-flight tandem mass spectrometer are described. The use of two MALDI matrixes, alpha-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB), is shown to control the nature and extent of fragmentation observed in collision-induced dissociation experiments on synthetic oligosaccharides. CHCA promotes the occurrence of glycosidic cleavages, whereas DHB promotes a wide range of fragmentations. These latter fragmentations include glycosidic cleavages, cross-ring cleavages, and the formation of "internal" cleavage ions, which are derived from elimination of substituents from around the pyranose ring. This extensive fragmentation is shown to facilitate the detailed structural characterization of high-mannose and hybrid-type N-glycans purified from avidin. Importantly, the cross-ring fragments reveal linkage information, unambiguously define antennae substitutions, and differentiate isomeric glycoforms.