Tandem mass spectrometry and differential ion mobility separation of sulfated glycosaminoglycans carbohydrates
Muchena, John Kailemia
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Glycosaminoglycans (GAGs) carbohydrates are biologically important molecules found in all the living organisms and efforts are made to identify their molecular structures in order to gain more understanding about their functions. Several tandem mass spectrometry (MS/MS) methods have been useful in structural characterization of GAGs. However, complete structural characterization of GAGs has remained elusive due to the inherent heterogeneity brought about by their non-template biosynthetic pathways. The highly sulfated and isomeric GAGs have remained relatively intractable to characterize. Highly sulfated GAGs have a tendency to lose SO3 during ion activation thus producing few or no structurally informative fragment ions. On the other hand, isomeric oligosaccharides produce isobaric molecular ions in the MS stage and generally have identical MS/MS fragmentation patterns. This work will highlight some of the recent contributions made towards addressing these two issues. By controlling the ESI solvent conditions using a small amount of NaOH (1-2 mM), highly sulfated GAG molecules can be stabilized and location of SO3 modifications identified using collision-induced dissociation (CID). Also, in some instances C5 epimeric state of the uronic acid residues can be obtained through the selection of the right molecular ions during CID activation. By use of field asymmetric-waveform ion mobility spectrometry (FAIMS), it is possible to separate isobaric ions and even diastereoisomers. The separated species can be fragmented using methods like electron detachment dissociation (EDD) to obtain useful structural information. Ion intensity spectral differences especially from isomeric compounds can be visualized using statistical methods like principal component analysis.