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Keywords: High performance liquid chromatography, capillary electrophoresis, MALDI-TOF mass spectrometry, NMR, cell wall oligosaccharides, arabinan, Arabidopsis thaliana, cell wall degrading enzymes, profiling The plant cell wall polysaccharides cellulose, hemicelluloses and pectins are very heterogeneous and complex structures consisting of at least 20 different sugars and 30 different linkage types. Additionally, hemicelluloses and pectins might be acetylated and/or feruloylated. Furthermore, pectins carry methyl esters. The degree and distribution of these modifications may vary significantly depending on source and developmental stage. In this research several analytical tools were developed for the analysis of complex mixtures of cell wall derived oligomers. The combination of 1) the use of pure and well-defined cellulases, hemicellulases and pectinases, and 2) the detection of the oligosaccharides released by MALDI-TOF MS and CE-LIF resulted in a screening method for Arabidopsis cell wall mutants, which addresses all enzyme-accessible polysaccharides in the cell wall. Porous graphitized carbon (PGC)-HPLC with evaporative light scattering and mass detection was introduced to a broad range of neutral and acidic cell wall polysaccharide derived oligosaccharides and separation of almost all oligosaccharides under investigation was achieved. The used gradient ensured 1) a sufficient separation of many oligosaccharides and 2) a sequential elution of first the neutral and then the acidic oligosaccharides. This elution behavior in combination with online-recorded MSn analysis facilitates the identification of (unknown) peaks. A wide range of branched arabino-oligosaccharides was isolated from sugar beet arabinan and characterized with NMR. HPAEC was demonstrated to have insufficient resolution to separate all linear and branched arabino-oligosaccharides. Therefore, PGC-HPLC-ELSD/MS and CE-LIF-MS were explored for the separation and detection of isomeric arabino-oligomers and were demonstrated to perform well. The combination of the controlled enzyme treatment, the predictive retention behavior on PGC-material, and the LC/CE-MS2 fragmentation patterns led to the prediction of the structures of unknown branched arabino-oligosaccharides in a complex mixture. |
