Structural characterization of arabinogalactan-II and pectin from Urtica cannabina

Abstract

Comparative analysis of extracellular and cell wall glycans from Urtica cannabina leaves was performed using chemical methods, GC, GC–MS, 1D, and 2D NMR spectroscopy. The structures of extracellular AG-II and cell wall AG-II are similar. The units are typical for AG-IIs: β-GlcpA-4-OMe-(1→, Rhap-(1 → 4)-β-GlcpA-(1→, attached to β-Galp at O-6, as well as arabinan chains attached to β-Galp at O-3. A single Araf and a trisaccharide formed by 2,5-Araf and two terminal Araf form short arabinan side chains in AG-II. 1,5-arabinan with a backbone substituted by a single Araf at O-3 was identified only in the side chains of cell wall AG-II. The side chains can be attached to O-3 and O-6 of the same β-Galp to form a bifurcated AG side chain. The backbone of AG-II is formed by 1,6- rather than 1,3-linked Galp, although it does include some 1,3-Galp. The high content of 3,6-Galp shows the highly branched nature of the AG carbohydrate chains. From the cell wall, AGP was extracted together with pectin, the simultaneous elution of which from both DEAE-cellulose and Sepharose may indicate a link between them.