Rhamnogalacturonan-II (RG-II) is a complex polysaccharide component of pectin that is found in the primary cell walls of dicotyledonous and monocotyledonous plants and gymnosperms.[1] It is supposed to be crucial for the plant cell wall integrity. RG-II is also likely to be present in the walls of some lower plants (ferns, horsetails, and lycopods). Its global structure is conserved across vascular plants, albeit a number of variations within the RGII side chains have been observed between different plants.[2] RG-II is composed of 12 different glycosyl residues including D-rhamnose, D-apiose, D-galactose, L-galactose, Kdo, D-galacturonic acid, L-arabinose, D-xylose, and L-aceric acid, linked together by at least 21 distinct glycosidic linkages. Some resides are further modified via methylation and acetylation. It moreover supports borate mediated cross-linking between different RGII side-chain apiosyl residues. The backbone consists of a linear polymer of alpha-1,4-linked D-galactopyranosiduronic acid. RG-II can be isolated from different sources, such as apple juice and red wine.[3]
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.[4]