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

A possible chain conformation of the acidic heteropolysaccharide isola ted from the fruit body of Tremella fuciformis Berk (Shirokikurage) wa s proposed by the X-ray diffraction study combined with the computatio nal model building technique. The polysaccharide consists of a linear backbone of 1,3-linked alpha-D-mannose which is highly substituted wit h beta-D-xylose, beta-D-glucuronic acid, and 1,2-linked beta-D-xylobio se units at the C2 position of the mannose residue. It was suggested f rom the X-ray data, together with the knowledge of the chain conformat ions proposed for other 1,3-linked alpha-D-glycans, that the backbone conformation has the left-handed, three-fold helical symmetry. Orienta tions of the side group residues on the mannan backbone were suggested from the theoretical calculations. The proposed conformation of a rep eating unit of the helical model consisted of six mannose residues and three side group residues in the 2.42 nm distance along the fiber axi s. Two interresidue hydrogen bonds were observed over each 1,2-linkage between the mannose residue and the side group residue, while no hydr ogen bond was observed over the backbone linkage.