Enzymatic synthesis and hydrolysis of xylogluco-oligosaccharides using the first archaeal a-xylosidase from Sulfolobus solfataricus

The first, recently identified, archaealxylosidase from
Sulfolobus solfataricus (XylS) shows high
specificity for hydrolysis of isoprimeverose [a-
-xylopyranosyl-(1,6)-D-glucopyranose, (X)], the p
-nitrophenyl-a derivative of isoprimeverose, and xyloglucan oligosaccharides and has transxylosidic activity, forming, in a retaining
mode, interesting a-xylosides. This article describes the synthesis
of isoprimeverose, the disaccharidic repeating unit of
xyloglucan, of thep-nitrophenyl-a 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 synthesis reactions of XylS, it
being a biocatalyst (i) active hydrolytically only on X-ending
substrates liberating a xylose molecule and (ii) capable of
transferring xylose only on the nonreducing end glucose of
p-nitrophenyl-(PNP)-a-D-cellobioside. The compounds synthesized
by this enzyme are a starting point for enzymological
studies of other new enzymes (i.e., xyloglucanases) for
which suitable substrates are difficult to synthesize. This
study also allows us to define the chemical characteristics of
the xylose-transferring activity of this new archaeal enzyme,contributing to building up a library of different glycosidases
with high specific selectivity for oligosaccharide synthesis.