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Review
. 2019 Jan 4;10(5):1272-1284.
doi: 10.1039/c8sc05426f. eCollection 2019 Feb 7.

In-depth structural analysis of glycans in the gas phase

Eike Mucha  1   2 , Alexandra Stuckmann  1   2 , Mateusz Marianski  1 , Weston B Struwe  3 , Gerard Meijer  1 , Kevin Pagel  1   2
Affiliations
Review

In-depth structural analysis of glycans in the gas phase

Eike Mucha et al. Chem Sci. .

Abstract

Although there have been substantial improvements in glycan analysis over the past decade, the lack of both high-resolution and high-throughput methods hampers progress in glycomics. This perspective article highlights the current developments of liquid chromatography, mass spectrometry, ion-mobility spectrometry and cryogenic IR spectroscopy for glycan analysis and gives a critical insight to their individual strengths and limitations. Moreover, we discuss a novel concept in which ion mobility-mass spectrometry and cryogenic IR spectroscopy is combined in a single instrument such that datasets consisting of m/z, collision cross sections and IR fingerprints can be obtained. This multidimensional data will then be compared to a comprehensive reference library of intact glycans and their fragments to accurately identify unknown glycans on a high-throughput scale with minimal sample requirements. Due to the complementarity of the obtained information, this novel approach is highly diagnostic and also suitable for the identification of larger glycans; however, the workflow and instrumentation is straightforward enough to be implemented into a user-friendly setup.

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Figures

Fig. 1
Fig. 1. (a) A generic glycan illustrating the structural features which lead to the immense diversity in this class of biomolecules. (b) The corresponding symbol depiction according to the symbol nomenclature for glycans (SNFG) which is illustrated in (c).
Fig. 2
Fig. 2. Principle of ion mobility spectrometry (IMS). In the ion mobility cell ions are separated according to their charge, size, and shape. The IM cell is filled with a neutral buffer gas such as helium or nitrogen. Gas-phase ions travel through the IM cell, guided by a weak electric field, in which larger ions (blue) undergo more collisions with the buffer gas and thus have longer drift times compared to more compact (green) ions.
Fig. 3
Fig. 3. (a) Symbol nomenclature for glycan representation. (b) IM-MS analysis of an isomeric glycopeptide mixture. Both glycopeptides differ within the glycan in the connectivity of the terminal sialic acid residue (α2–6 and α2–3). (c) In a mixture, the [M + 3H]3+ (m/z 991) ions exhibit a single drift peak, which does not allow a separation of the two intact glycopeptides. (d) When the protonated glycopeptide precursor is fragmented prior to the IM cell, trisaccharide fragments with diagnostic drift times and CCSs are obtained.,
Fig. 4
Fig. 4. Schematic diagram of the experimental setup. Parent or fragment ions in the gas phase are mass-to-charge selected and accumulated inside an ion trap. Traversing helium droplets can pick up trapped ions, and these are immediately cooled to 0.37 K. Subsequently, the doped droplets are irradiated with IR radiation of a defined wavelength using the free-electron laser.
Fig. 5
Fig. 5. Unique IR spectra of trisaccharides 6–11, that only differ in the connectivity (1,3 or 1,4), configuration (α or β) or composition (Glc or Gal) of the terminal building block. Reproduced from ref. 77 with permission from Wiley and Sons, copyright 2017.
Fig. 6
Fig. 6. Schematic view of a disaccharide illustrating the interrelated structural features that influence the conformation of glycans: hydrogen bonding patterns or networks, the torsional angles φ and φ of the glycosidic bond and the ring puckering of individual building blocks.
Fig. 7
Fig. 7. A possible database structure to aid the reliable identification of glycans including the m/z values of parent and fragment ions, their corresponding CCSs and IR fingerprints.
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