Structural Characterization of an Arabinogalactan-Protein from the Fruits of Lycium ruthenicum

A water-soluble arabinogalactan-protein (AGP), designated LRGP3, was isolated from the fruits of Lycium ruthenicum Murr. Its average molecular weight was 75.6 kDa. Monosaccharide composition analysis revealed that it was composed of rhamnose, arabinose, and galactose in a molar ratio of 1.0:14.9:10.4. Protein accounted for 1.7% of the AGP and was rich in hydroxyproline. On the basis of monosaccharide composition, partial acid hydrolysis, methylation analysis, ESI-MS, and NMR spectroscopy, LRGP3 was characterized as a highly branched polysaccharide with a backbone of (1→3)-linked β-D-galactopyranosyl residues, many of which were substituted at the O-6 position by galactosyl or arabinosyl groups. The branches were composed of (1→5)-linked arabinose, (1→2)-linked arabinose, (1→6)-linked galactose, (1→3)-linked galactose, and (1→2,4)-linked rhamnose, and the major nonreducing termini were α-L-arabinofuranosyl residues.