Synthesis and hydrolysis of 1,3-beta-xylosidic linkages by endo-1,4-beta-xylanase of Cryptococcus albidus

Purified extracellular endo-1,4-beta-xylanase (EC 3.2.1.8) of the yeast Cryptococcus albidus was found to catalyze not only the known 1,4-beta-transfer, but an alternative transglycosylation reaction leading to the formation of 1,3-beta-glycosidic linkages. From a mixture of products of beta-xylanase degradation of phenyl beta-D-xylopyranoside three xylooligosaccharide fractions, differing chromatographically from the 1,4-beta-linked products, were isolated by preparative paper chromatography. Their structure was elucidated by mass spectrometry, 13C-NMR spectroscopy and enzymic hydrolysis by beta-xylanase and beta-xylosidase. The isomeric xylotriose was identified as 3-O-beta-D-xylopyranosyl-4-O-beta-D-xylopyranosyl-D-xylose. The fraction of isomeric tetrasaccharides was found to be represented mainly by 4-O-beta-D-xylopyranosyl-3-O-beta-D-xylopyranosyl-4-O-beta-D-xylopyranosyl- D-xylose. The xylooligosaccharides containing one 1,3-beta-linkage were also produced on the enzyme treatment of 1,4-beta-xylotriose and 1,4-beta-xylan. When treated with the enzyme responsible for their synthesis, the isomeric xylooligosaccharides were hydrolyzed at the 1,3-beta-linkage, despite the fact the enzyme does not attack 1,3-beta-xylan. The results are interpreted in the relation to the characterized four-subsite substrate-binding site of the enzyme.