Cross-Ring Fragmentation Patterns in the Tandem Mass Spectra of Underivatized Sialylated Oligosaccharides and Their Special Suitability for Spectrum Library Searching.

ABSTRACT: Reference spectral library searching, while widely used to identify compounds in other areas of mass spectrometry, is not commonly used in glycomics. Building on a study by Cotter and coworkers on analysis of sialylated oligosaccharides using atmospheric pressure-matrix-assisted laser-induced tandem mass spectrometry (MS/MS), we show that library search methods enable the automated differentiation of such sialylated oligosaccharide isomers using MS/MS derived from electrospray collision-induced dissociation in ion trap and beam-type fragmentation mass spectrometers. We compare MS/MS spectra of five sets of native sialylated oligosaccharide isomers and show a spectral library search method that can distinguish between these isomers using the precursor ion [M+2X-H]+, where X=Li, Na, or K. Sialic acid linkage (?2,3 vs. ?2,6) is known to have a dramatic effect on the fragmentation of the sialylated compounds. We found that 2,4A3 cross-ring fragment at the terminal monosaccharide in sialyllactoses, sialyllactosamines, and sialyl pentasaccharides is highly abundant in the MS/MS spectra of [M+2X-H]+ species of ?2,6-NeuAc glycans, while (2,4A3-H2O) fragment is highly abundant in ?2,3-NeuAc moiety. The 2,4A3-H2O peak is specific to NeuAc-?2,3-Gal-?1,4-Y (Y=GlcNAc or Glc). To our knowledge, this observation was not reported previously. Theoretical calculations reveal major conformational differences between ?2,6-NeuAc and ?2,3-NeuAc structures that provide reasonable explanations for the observed fragmentation patterns. Other singly-charged ions ([M+X]+) do not show similar cross-ring cleavages. Implemented in a searchable library, these spectral differences provide a facile method to distinguish sialyl isomers without derivatization. We also found good spectral matching across instruments. MS/MS spectra and tools are available at http://chemdata.nist.gov/glycan/spectra . Graphical Abstract.

SUBMITTER: De Leoz MLA 

PROVIDER: S-EPMC6416239 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature