Structural studies of water-soluble pectic polysaccharides and arabinogalactan protein from pine (Pinus sylvestris)...

This paper presents the first experimental evidence for the presence of water-soluble arabinogalactan proteins (AGPs) and pectin polysaccharides in the coniferous greens of Pinus sylvestris. The polymers under scrutiny consisted of a β-(1→3)-galactan core to which side chains of β-(1→6)-linked galacto-oligosaccharides were attached via O-6. These oligosaccharides also contained a combination of acidic β-D-GlcpA and 1,4-β-D-GlcpA residues, as well as neutral T-β-Galp, T-α-L-Rhap and T-α-L-Fucp residues. At position 3, the β-(1→6)-galactan side chains are partially substituted with T-Araf, 1,3- and/or 1,5-linked α-L-Araf residues. Analysis revealed a distinctive glycosylation pattern of AGP-like glycoproteins derived from Pinus sylvestris. The most significant finding was the verification of the existence of 4-O-methyl-fucose. The L-Fuc residues were identified on side branches and found to be bound to 1,4-linked β-D-GlcpA, forming the sequence 4-O-Me-α-L-Fucp-(1→4)-β-D-GlcpA-(1→. The main polymers identified in the fragments obtained by partial degradation through acid hydrolysis and the anion-exchange chromatography method, followed by enzymatic cleavage with exo- and endo-1,4-α-D-polygalacturonase, were AGPs and rhamnogalacturonan I (RG-I). It can be concluded that a significant proportion of AGPs are strongly associated with RG-I, suggesting that they are directly linked, which is important for understanding the structure-function interactions of these molecules.