Structure of β-1,3-xylooligosaccharides generated from Caulerpa racemosa var. laete-virens β-1,3-xylan by the action of β-1,3-xylanase

Recently we reported the molecular cloning and characterization of a novel β-1,3-xylanase from the marine bacterium Vibrio sp. AX-4 [Kiyohara et al. (2005) Biochem. J. 388, 949-957]. We report here the structural analysis of oligosaccharides generated from β-1,3-xylan of a siphonous green alga, Caulerpa racemosa var. laete-virens, by the action of β-1,3-xylanase. The enzyme degraded the polysaccharide producing oligosaccharides with different R_fs on TLC (EX2-EX5). Sugar component, linkage, and MALDI-TOF-MS analyses revealed that EX2 and EX3 were Xyl-1,3-Xyl and Xyl-1,3-Xyl-1,3-Xyl, respectively. On the other hand, EX4 was a mixture of Glc-1,3-Xyl-1,3-Xyl, Xyl-1,4-Xyl-1,3-Xyl and Xyl-1,3-Xyl-1,4-Xyl, while EX5 was a mixture of tetra-saccharides containing 3-substitued GIc in addition to the same components of EX4. Branching was not likely present in EXOs prepared from the polysaccharide by the enzyme. These results strongly suggest that the C. racemosa β-1,3-xylan is a linear heteropolysaccharide containing 1,3-Glc and 1,4-Xyl both of which are thought to be located within a β-1,3-Xyl chain and linked via covalent bonds. This report indicates the usefulness of the enzyme for the structural analysis of β-1,3-xylan.