Abstract

Aspergillus oryzae produces hydrolases involved in xyloglucan degradation and induces the expression of genes encoding xyloglucan oligosaccharide hydrolases in the presence of xyloglucan oligosaccharides. A gene encoding α-xylosidase (termed AxyA), which is induced in the presence of xyloglucan oligosaccharides, is identified and expressed in Pichia pastoris. AxyA is a member of the glycoside hydrolase family 31 (GH31). AxyA hydrolyzes isoprimeverose (α-D-xylopyranosyl-(1→6)-D-glucopyranose) into D-xylose and D-glucose and shows hydrolytic activity with other xyloglucan oligosaccharides such as XXXG (heptasaccharide, Glc4Xyl3) and XLLG (nonasaccharide, Glc4Xyl3Gal2). Isoprimeverose is a preferred AxyA substrate over other xyloglucan oligosaccharides. In the hydrolysis of XXXG, AxyA releases one molecule of D-xylose from one molecule of XXXG to yield GXXG (hexasaccharide, Glc4Xyl2). AxyA does not contain a signal peptide for secretion and remains within the cell. The intracellular localization of AxyA may help determine the order of hydrolases acting on xyloglucan oligosaccharides.

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