Aims and Concepts

The demand of current societies, with ever-increasing populations, for food and energy grows dramatically, resulting in a clear need for increased crop productivity. Additionally, the utilization of agricultural waste products for the production of fuels, chemicals, and new bio-based materials such as bioplastics must be strongly improved to enable a carbon neutral economy in the future. With our interdisciplinary research at the interface of synthetic organic chemistry and plant biology, we try to contribute to solving these issues. We focus on elucidating plant cell wall structure and biosynthesis as well as on obtaining a better understanding of plant immunity. To meet these goals, we use chemical synthesis and enzymatic methods to prepare glycans ranging in the size from oligo- to polysaccharides. The extensive use of glycan array technology allows us to employ these glycans for the high-throughput analysis of glycosyltransferases involved in cell wall biosynthesis, plant immune receptors, and other glycan-binding proteins. Furthermore, we investigate the physical properties of the prepared glycans in collaborations with researchers in chemical engineering and biopolymer technology.

Chemical Synthesis of Plant Cell Wall-related Oligosaccharides

Plants produce an enormous diversity of glycans that fulfill essential roles during the life cycle of the plant. The glycome of plants contains many unique glycans that are not found in animals but are still mostly conserved across the plant kingdom. The vast majority of plant glycans are part of the cell wall. Oligosaccharide fragments of plant cell wall glycans are powerful research tools for plant cell wall biology, but are notoriously difficult to obtain from natural sources. In our lab we chemically synthesize homogenous oligosaccharides using solution-phase chemistry and automated glycan assembly on a solid support. Currently, we have assembled a library of xylan, xyloglucan, mixed-linkage glucan, and arabinogalactan oligosaccharides that have been utilized for the characterization of cell wall-biosynthetic and -degrading enzymes and plant cell wall-directed antibodies. This library of plant oligosaccharides is constantly extended.

A Plant Glycan Microarray as Tool for Plant Cell Wall Research

Glycan microarrays have emerged as a powerful tool for high-throughput analyses of carbohydrate-protein interactions. We have established this technology in our lab to analyze and characterize plant cell wall-directed antibodies, cell wall polysaccharide-degrading and -remodeling enzymes, as well as glycosyltransferases involved in plant cell wall biosynthesis. We have printed our library of plant cell wall-related oligosaccharides onto glass slides with activated surfaces. The immobilized glycans can be analyzed for interactions with glycan-binding proteins or for their ability to serve as a substrate for carbohydrate-active enzymes. For example, we have mapped the binding epitopes of 78 plant cell wall-directed monoclonal antibodies. These antibodies are widely used for high resolution microscopic analyses of plant cell walls. Moreover, we are currently establishing a glycan microarray assay for the high-throughput analyses of plant glycosyltransferase enzymes. This assay will immensely accelerate the identification of new cell wall biosynthetic glycosyltransferases.

  • C. Ruprecht, M. P. Bartetzko, D. Senf, P. Dallabernadina, I. Boos, M. C. F. Andersen, T. Kotake, J. P. Knox, M. G. Hahn, M. H. Clausen, F. Pfrengle, Plant Physiol. 2017, 175, 1094-1104.
  • C. Ruprecht, A. Geissner, P. H. Seeberger, F. Pfrengle, Carb. Res. 2019, 481, 31-35.
  • C. Ruprecht, P. Dallabernardina, P. J. Smith, B. R. Urbanowicz, F. Pfrengle, ChemBioChem 2018, 19, 793-798.

Chemo-enzymatic Synthesis of Plant Polysaccharides

While chemical synthesis provides access to defined oligosaccharides, the synthesis of larger structures is difficult, due to the many reactions and purification steps involved. Enzymatic polymerization of chemically synthesized oligosaccharides can provide tailor-made polysaccharides with defined branching patterns. For the synthesis of xylan polysaccharides we have used a “glycosynthase” enzyme, which is a genetically inactivated glycosyl hydrolase. This enzyme is able to transfer fluorinated oligosaccharides as glycosyl donors to suitable glycosyl acceptors. Using this glycosynthase, chemically synthesized arabinoxylan oligosaccharides were polymerized, providing a series of xylan polysaccharides with defined patterns of arabinose substitution. These previously unavailable structures were characterized regarding their crystallinity and their ability to interact with cellulose surfaces. Our results support previous studies on native plant material, suggesting that xylan adopts a three-fold helical screw in solution, but converts into a two-fold helical screw upon interaction with cellulose. As a result, the strength of xylan-cellulose interactions depends on the xylan substitution pattern, a fact that might be explored for improving wood as a material through targeted modifications of wood stability and stiffness.

  • D. Senf, C. Ruprecht, S. Kishani, A. Matic, G. Toriz, P. Gatenholm, L. Wagberg, F. Pfrengle, Angew. Chem. Int. Ed. 2018, 57, 11987-11992.