Structural studies of water-extractable pectic polysaccharides and arabinogalactan proteins from Picea abies greenery

Water-extractable arabinogalactan proteins (AGP) (the main constituent) and pectic polysaccharides were isolated from tree greenery of Picea abies. The carbohydrate part of AGP macromolecules consisted of AG-II, the side chains of which were represented by 1,6- and 1,3,6-β-d-Galp, T-α-l-Araf, 1,3- and 1,5-α-l-Araf, T-β-D-GlcpA and 1,4-β-D-GlcpA, T-α-l-Rhap, T-α-l-Fucp and 4-O-Me-α-l-Fucp residues. It was established that the unusual 4-O-Me-α-l-Fucp monosaccharide are located on the non-reducing ends of the side chains of carbohydrate part of AGP macromolecules, and are bound to 1,4-β-d-GlcpA residues by 1,4-bonds. The backbone of pectin macromolecules consisted mostly of 1,4-α-d-galactopyranosyluronan and RG-I, which side chains were represented by highly branched 1,5-α-l-arabinan. It was shown that RG-I is characterized mainly by short segments, which are alternated with the regions of the non-acetylated and non-methyl-esterified galacturonan. The study revealed that at least a part of the pectin is strongly associated with AGP. It was indicated that the RG-I segments are separated from the AGP-bound pectin by regions of 1,4-α-d-galactopyranosyluronane.