Fig. 5.

Glycotope-centric glycomic analysis of N-glycans from mouse brain striatum. A, MALDI-MS mapping of the permethylated N-glycans, with major peaks annotated using the standard symbol nomenclature system ((35) and (http://www.ncbi.nlm.nih.gov/books/NBK310273/)), based primarily on glycosyl composition. Several isomeric permutations for the actual glycotopes carried on each structure are possible and indeed verified by subsequent LC-MS²/MS³ analyses. Data analysis by Glypick allows rapid identification and assessment of the relative abundance of expressed glycotopes at glycomic level based on the summed intensity of diagnostic MS² ions (B), and MS³ ions in the case of isomeric fucosylated and disialylated Hex₁HexNAc₁ (C). N-glycans carrying the disialylated glycotopes can be inferred from the compiled data (supplemental Table S4) and verified by manual interpretation of their respective MS² scans averaged over their elution time, exemplified here for a disialylated mono-antennary N-glycan (D), and 2 tetra-sialylated tatra-antennary N-glycans carrying either one (E) or two (F) fucoses. For the latter two, more than one isomeric structures are clearly present based on the complement of oxonium ions detected. The MS² data will not inform which specific glycotopes are carried on which of the 4 antennae. All MS² ions are singly charged except those annotated with 2+ or 3+.