August 2, 2018 at 5:00 am

Chemistry Colloquium | Complex Arabinogalactan-proteins in Duckweed, Nov. 19

Ohio University’s Chemistry & Biochemistry Colloquium Series presents Ohio University alum Dr.Li Tan ’03Ph.D. on Complex Arabinogalactan-proteins in Duckweed Monday, Nov. 19, from 4:10 to 5 p.m. in Clippinger 194.

Abstract: A complex arbinogalactan-protein (cAGPs) has been isolated from the growth medium of suspension-cultured Arabidopsis cells and shown to contain covalently linked arabinoxylan, pectin, and arabinogalactan (AG), which is named Arabinoxylan-Pectin-Arabiogalactan-Protein 1 (APAP1). However, the existence of such cAGPs in plant tissues remains to be demonstrated. Here, we report the isolation and structural characterization of an APAP1-like cAGPs from the duckweed Spirodela polyrhiza and provide evidence that it contains covalently linked apiose-containing pectins and xylan oligomers. Specifically, an AGP fraction was solubilized from the alcohol-insoluble residue generated from S. polyrhiza and purified using procedures we developed to isolate APAP1. The AGPs were shown by glycosyl residue and linkage composition analyses to contain pectin, xylan, and type II AG. One and two-dimensional NMR spectroscopy demonstrated the presence of structural elements characteristic of apiosyl-pectin, xylan, and type II AG in the AGP fraction. Treating the AGPs with an AGP-specific exo-1,3-galactanase generated a mixture of oligo/polysaccharides that contained Api, Rha, GalA, Xyl, Ara, Gal, and GlcA residues. NMR analyses of the oligo/polysaccharides confirmed the presence of structural elements of apiosyl-pectin and xylan in these oligo/polysaccharides, and suggested that the apiosyl-pectin and xylan oligomers are attached to the side chains of AG. ¹¹B-NMR spectroscopy showed that the cAGPs contained bound boron in the form of a 1:1 boric acid-diol ester. The possibility of forming cAGP dimer through 1:2 borate-diol ester and the corresponding function was also discussed.