Enzymatic synthesis and hydrolysis of xylogluco-oligosaccharides using thefirst archaeal alpha-xylosidase from Sulfolobus solfataricus

The first, recently identified, archaeal alpha -xylosidase from Sulfolobus solfataricus (XylS) shows high specificity for hydrolysis of isoprimeverose [alpha -D-xylopyranosyl-(1,6)-D-glucopyranose, (X)], the p-nitrophenyl-bet a derivative of isoprimeverose, and xyloglucan oligosaccharides and has tra nsxylosidic activity, forming, in a retaining mode, interesting alpha -xylo sides. This article describes the synthesis of isoprimeverose, the disaccha ridic repeating unit of xyloglucan, of the p-nitrophenyt-beta derivative of isoprimeverose, and of a trisaccharide based on isoprimeverose that is one of the trisaccharidic building blocks of xyloglucan. A substrate structure -activity relationship is recognized for both the hydrolysis and the synthe sis reactions of XylS, it being a biocatalyst (i) active hydrolytically onl y on X-ending substrates liberating a xylose molecule and (ii) capable of t ransferring xylose only on the nonreducing end glucose of p-nitrophenyl-(PN P)-beta -D-cellobioside. The compounds synthesized by this enzyme are a sta rting point for enzymological studies of other new enzymes (i.e., xylogluca nases) for which suitable substrates are difficult to synthesize. This stud y also allows us to define the chemical characteristics of the xylose-trans ferring activity of this new archaeal enzyme, contributing to building up a library of different glycosidases with high specific selectivity for oligo saccharide synthesis.