Structural elucidation of an anti-metastatic polysaccharide from the peels of Korean citrus Hallabong

Abstract

Previously, we have reported that the polysaccharide, HBE-III, purified from the peel of the Korean citrus Hallabong, potently inhibits tumor-metastasis. In this paper, the primary structure of HBE-III was elucidated. HBE-III is a 10 kDa acidic polysaccharide, which contains 15 different monosaccharides and 23 glycosyl linkages, indicating it is a highly branched complex polysaccharide. To determine its microstructure, sequential acid hydrolysis was carried out and the resulting fragments were analyzed using composition, methylation, and MS/MS analyses. The results indicate that HBE-III is composed of a main chain with a α-(1→4)-galacturono-oligosaccharide unit and four groups of side chains including an uronic acid-rich octasaccharide (side chain A), aceric acid-containing nonasaccharide (side chain B), Rhap-(1→5)-Kdo (side chain C), and Araf-(1→5)-Dha (side chain D), which is characteristic of rhamnogalacturonan II. The results of our ¹¹B-NMR analysis suggest that HBE-III exists as an RG-II dimer and this structure contributes to the anti-metastatic activity of HBE-III.

Keywords: Hallabong; Korean citrus; Pectin; Polysaccharide; Rhamnogalacturonan-II; Structure-function relationship.