Freie Universität Berlin
Automated Glycan Assembly of Hemicellulosic Oligosaccharides from the Plant Cell Wall.
Degree: PhD, FB Biologie, Chemie, Pharmazie, 2017, Freie Universität Berlin
The plant cell wall is the outer-layer of the cell and controls its volume and shape. It plays an important structural role and is involved in the plant’s immune response against pathogens. Plant cell walls are composed of a mixture of simple and complex biopolymers that are mainly comprised of highly complex polysaccharides. Well-defined oligosaccharides related to plant cell wall polysaccharides are fundamental molecular tools for studying cell wall structure and biosynthesis, but are difficult to obtain from natural sources. The chemical synthesis of plant oligosaccharide libraries is thus a promising approach for advancing cell wall research.
Automated glycan assembly is a powerful emerging technique for the solid-phase synthesis of oligosaccharides. Through the iterative addition of different building blocks (BB) to a functionalized solid support, glycans of different lengths and branching patterns can be produced. In this work, automated glycan assembly has been used to obtain well-defined oligosaccharide fragments of the cell wall polysaccharides xyloglucan (XG) and mixed-linkage glucan (MLG). These compounds were applied for the characterization of cell wall glycan-directed monoclonal antibodies and cell wall-modifying enzymes.
In Chapter 2, which constitutes the main part of this thesis, the synthesis of XG oligosaccharides is described. XGs are the main hemicellulosic polysaccharides in higher plants. They are made of a cellulosic backbone highly decorated with xylose residues that can be further substituted with galactose and fucose. Initially, we tested the possibility to use exclusively monosaccharide BBs for the assembly of the target oligosaccharides. However, this approach did not provide good -stereoselectivity when glycosylating backbone glucose residues with xylose. Therefore, a disaccharide BB carrying a pre-installed -glycosidic linkage between glucose and xylose was synthesized. Using this disaccharide BB a library of XG oligosaccharides was successful prepared. To synthesize galactosylated XG oligosaccharides p-methoxybenzyl was used at the C2-position of the xylose. This represents the first example for the use of this temporary protecting group in automated glycan assembly. In collaboration with Dr. Ruprecht, the synthetic XG oligosaccharides were used for the characterization of monoclonal antibodies (mAbs) that recognize cell wall polysaccharides and for determining the binding specificities of xyloglucan endotransglycosylases (XETs), important enzymes involved in remodeling the cell wall during cell growth.
In chapter 3, a library of MLG oligosaccharides was synthesized by automated glycan assembly. MLGs are an important class of hemicellulose polymers present in grass and cereals. They are constructed from a backbone of cellulosic oligosaccharide stretches randomly connected by -1,3-glycosidic linkages. Using two differently protected glucose building blocks, a library of MLG oligosaccharides up to an octasaccharide was synthesized. MLGs are degraded by an enzyme named…
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APA (6th Edition):
Dallabernardina, P. (2017). Automated Glycan Assembly of Hemicellulosic Oligosaccharides from the Plant Cell Wall. (Doctoral Dissertation). Freie Universität Berlin. Retrieved from http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000106040
Chicago Manual of Style (16th Edition):
Dallabernardina, Pietro. “Automated Glycan Assembly of Hemicellulosic Oligosaccharides from the Plant Cell Wall.” 2017. Doctoral Dissertation, Freie Universität Berlin. Accessed June 21, 2018.
MLA Handbook (7th Edition):
Dallabernardina, Pietro. “Automated Glycan Assembly of Hemicellulosic Oligosaccharides from the Plant Cell Wall.” 2017. Web. 21 Jun 2018.
Dallabernardina P. Automated Glycan Assembly of Hemicellulosic Oligosaccharides from the Plant Cell Wall. [Internet] [Doctoral dissertation]. Freie Universität Berlin; 2017. [cited 2018 Jun 21].
Available from: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000106040.
Council of Science Editors:
Dallabernardina P. Automated Glycan Assembly of Hemicellulosic Oligosaccharides from the Plant Cell Wall. [Doctoral Dissertation]. Freie Universität Berlin; 2017. Available from: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000106040