XylS is a glycosyl hydrolase family 31 (GH31) alpha-xylosidase found in prokaryotes, eukaryotes, and archaea, that catalyzes the release of alpha-xylose from the non-reducing terminal side of the alpha-xyloside substrate. XylS has been characterized in Sulfolobus solfataricus where it hydrolyzes isoprimeverose, the p-nitrophenyl-beta derivative of isoprimeverose, and xyloglucan oligosaccharides, and has transxylosidic activity. All GH31 enzymes cleave a terminal carbohydrate moiety from a substrate that varies considerably in size, depending on the enzyme, and may be either a starch or a glycoprotein. The XylS family corresponds to subgroup 3 in the Ernst et al classification of GH31 enzymes.
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