Rhamnogalacturonan II from the leaves of Panax ginseng C.A. Meyer as a macrophage Fc receptor expression-enhancing polysaccharide

Abstract

A complex pectic polysaccharide (GL-4IIb2) has been isolated from the leaves of Panax ginseng C.A. Meyer, and shown to be a macrophage Fc receptor expression-enhancing polysaccharide. The primary structure of GL-4IIb2 was elucidated by composition. 1H NMR, methylation, and oligosaccharide analyses. GL-4IIb2 consisted of 15 different monosaccharides which included rarely observed sugars, such as 2- O-methylfucose, 2- O-methylxylose, apiose, 3-C- carboxy-5-deoxy- l- xylose (aceric acid, AceA), 3-deoxy- d- manno-2-octulosonic acid (Kdo), and 3-deoxy- d- lyxo-2-heptulosaric acid (Dha). Methylation analysis indicated that GL-4IIb2 comprised 34 different glycosyl linkages, such as 3,4-linked Fuc, 3- and 2,3,4-linked Rha, and 2-linked GlcA, which are characteristic of rhamnogalacturonan II (RG-II). Sequential degradation using partial acid hydrolysis indicated that GL-4IIb2 contained α-Rha p-(1 → 5)-Kdo and Ara f-(1 → 5)-Dha structural elements, an AceA-containing oligosaccharide, and uronic acid-rich oligosaccharide chains in addition to an α-(1 → 4)-galacturono-oligosaccharide chain. FABMS and methylation analyses suggested that the AceA-containing oligosaccharide was a nonasaccharide in which terminal Rha was additionally attached to position 3 of 2-linked Ara p of the octasaccharide chain observed in sycamore RG-II. Component sugar and methylation analyses assumed that the uronic acid-rich oligosaccharides possessed a similar structural feature as those in sycamore RG-II. GL-4IIb2 had a larger molecular mass (11,000) than sycamore RG-II (∼5000). A structure of macrophage Fc receptor expression-enhancing polysaccharide from the leaves of Panax ginseng C.A. Meyer has been characterised to be a rhamnogalacturonan II type polysaccharide containing a characteristic nonasaccharide sequence.