CHAIN CONFORMATION OF A GLUCURONO-XYLO-MANNAN ISOLATED FROM FRUIT BODY OF TREMELLA-FUCIFORMIS BERK

A possible chain conformation of the acidic heteropolysaccharide isolated from the fruit body of Tremella fuciformis Berk (Shirokikurage) was proposed by the X-ray diffraction study combined with the computational model building technique. The polysaccharide consists of a linear backbone of 1,3-linked alpha-D-mannose which is highly substituted with beta-D-xylose, beta-D-glucuronic acid, and 1,2-linked beta-D-xylobiose units at the C2 position of the mannose residue. It was suggested from the X-ray data, together with the knowledge of the chain conformations proposed for other 1,3-linked alpha-D-glycans, that the backbone conformation has the left-handed, three-fold helical symmetry. Orientations of the side group residues on the mannan backbone were suggested from the theoretical calculations. The proposed conformation of a repeating unit of the helical model consisted of six mannose residues and three side group residues in the 2.42 nm distance along the fiber axis. Two interresidue hydrogen bonds were observed over each 1,2-linkage between the mannose residue and the side group residue, while no hydrogen bond was observed over the backbone linkage.