Rhamnogalacturonan-II
Rhamnogalacturonan-II is a complex polysaccharide termed a pectin that is found in the primary walls of dicotyledenous and monocotyledenous plants and gymnosperms. RG-II is also likely to be present in the walls of some lower plants. Its structure is conserved across vascular plants. RG-II is composed of 12 different glycosyl residues including D-rhamnose, apiose, D-galactose, L-galactose, Kdo, galacturonic acid, L-arabinose, xylose, and L-aceric acid, linked together by at least 21 distinct glycosidic linkages. It also contains a borate cross-link between apiosyl residues. The backbone consists of a linear polymer of alpha-1,4-linked D-galactopyranosiduronic acid. RG-II can be isolated from apple juice and red wine.
The gut bacterium Bacteroides thetaiotaomicron has a polysaccharide utilization locus that contains enzymes that allows deconstruction of rhamnogalacturonan-II, cleaving all but 1 of its 21 distinct glycosidic linkages.
