Synthesis and biochemical application of rhamnogalacturonan-II oligosaccharides
Abstract
Wider research context: Plant cell walls provide the richest available resource of fermentable carbohydrates and bio-based materials. Optimal exploitation of this resource requires an in-depth knowledge of the molecular structure and biosynthesis of plant cell wall glycans. Besides cellulose, which is constructed from relatively simple -1,4-glucan chains, plant cell walls also contain the structurally more complex heteropolysaccharides hemicelluloses and pectin as well as lignin and cell wall proteins. The most complex cell wall glycan is rhamnogalacturonan-II (RG-II), a highly conserved low-molecular-weight pectic polysaccharide, containing twelve different types of monosaccharides that are connected through 20 different linkages. Pure oligosaccharide samples that represent structural features of complex cell wall glycans such as RG-II are powerful molecular tools for various biochemical assays and indispensable for continuous progress in plant cell wall research, but are of limited availability. Objectives: We will develop synthetic strategies to access oligosaccharide fragments of RG-II, which will be employed in glycan array assays aiming at the identification and characterization of RG-II-specific antibodies and RG-II-biosynthetic enzymes. Approach: The complex structure of RG-II poses enormous challenges for organic chemists: 1) The rare monosaccharides apiose and aceric acid need to be synthesized de novo and converted into suitable glycosyl donors. 2) The high number of uronic acid residues mandates a post-assembly-oxidation strategy. 3) The highly branched, congested structure of RG-II complicates the design of a suitable convergent synthetic strategy. 4) A large number of 1,2-cis-glycosidic bonds must be prepared in a stereoselective manner using individually optimized glycosylation protocols. Through utilization and further development of the most recent methodologies in synthetic carbohydrate chemistry these challenges will be met, and a collection of complex RG-II fragments up to the size of decasaccharides will be prepared. The prepared oligosaccharides will be printed as glycan arrays and screened with pectin-directed antibodies as well as putative glycosyltransferases (GTs) responsible for RG-II biosynthesis. Innovation: The availability of highly complex RG-II fragments will for the first time enable the systematic elucidation of RG-II biosynthesis and the detection and monitoring of specific RG-II epitopes within plant cell walls using fluorescence microscopy. The generated knowledge will facilitate future developments towards improved biomass digestibility, material strength of plant-derived products, and the shelf life of fruits and vegetables.
Publikationen
Project staff
Fabian Pfrengle
Univ.Prof. Dipl.-Chem. Dr.rer.nat. Fabian Pfrengle
fabian.pfrengle@boku.ac.at
Tel: +43 1 47654-77356
Project Leader
01.04.2022 - 31.03.2025