Sialylation analysis of O-glycosylated sialylated peptides from urine of patients suffering from Schindler's disease by Fourier transform ion cyclotron resonance mass spectrometry and sustained off-resonance irradiation collision-induced dissociation.

A strategy based on Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) for screening of complex glycoconjugate mixtures containing O-linked glycopeptides and O-glycosylated amino acids with alpha-N-acetylgalactosaminyl residues is presented. To detect and identify O-glycoforms present in urine of patients suffering from hereditary N-acetylhexosaminidase deficiency (known as Schindler's disease), present at 100 times higher concentrations than in urine of healthy controls, new accurate methods for mapping and sequencing were required. In the mass spectrometric analysis particular attention has to be paid to original sialylation patterns, because of the potential lability of the sialic acid moiety during the desorption/ionization process. Negative ion nanoelectrospray ionization (nanoESI) FTICR-MS at 9.4 T is shown here to represent a method of choice for identification of single components in such complex glycomixtures due to high resolution and mass accuracy. By optimization of sustained off-resonance irradiation collision-induced dissociation tandem mass spectrometry (SORI-CID-MS(2)) in the negative ion mode, the type and sequence of the sialylated glycopeptide components were determined from their fragmentation patterns. Additionally, implementation of SORI-CID-MS(3) provides detailed information for sialylation analysis. The potential diagnostic value of this approach is discussed.