MALDI-QTOFMS/MS identification of glycoforms from the urine of a CDG patient Original Research ArticleMALDI-QTOFMS/MS identification of glycoforms from the urine of a CDG patient Original Research Article

Identification of single glycoconjugate components in a complex mixture from the urine of a patient suffering from a congenital disorder of glycosylation was probed by MALDIMS analy-sis on a hybrid quadrupole time-of-flight instrument. In negative ion mode, complex maps con-taining more than 50 ionic species were obtained and a number of molecular ions directly as-signed using a previously developed computer-assisted algorithm. To confirm the data and determine the carbohydrate sequence, single molecular ions were selected and submitted to fragmentation experiments. Interpretation of fragmentation spectra was also assisted by the soft-ware using alignment with spectra generated in silico. According to fragmentation data, the ma-jority of glycoconjugate ionic species could be assigned to free oligosaccharides along with ten species tentatively assigned to glycopeptides. Following this approach for glycan identification by a combination of MALDI-QTOFMS and MS/MS experiments, computer-assisted assignment and fragment analysis, data for a potential glycan data base are produced. Of high benefit for this approach are two main factors: low sample consumption due to the high sensitivity of ion forma-tion, and generation of only singly charged species in MALDIMS allowing interpretation with-out any deconvolution. In this experimental set-up, sequencing of single components from the MALDI maps by low energy CID followed by computer-assisted assignment and data base search is proposed as a most efficient strategy for the rapid identification of complex carbohy-drate structures in clinical glycomics.