Glycosynthase‐Assisted Synthesis of Xylo‐Gluco‐Oligosaccharide Probes for α‐Xylosyltransferases

An efficient chemo‐enzymatic synthesis involving glycosylation catalyzed by E197A nucleophile mutant of the retaining endo‐cellulase Cel7B from Humicola insolens afforded well defined xylo‐gluco‐oligosaccharides. The synthesis of these complex oligosaccharides requires the use of an enzymatic protection/deprotection concept to allow a single‐step condensation of donors onto acceptors. These molecules were tested as potential acceptor substrates for two Arabidopsis thaliana putative xyloglucan α‐xylosyltransferases expressed in insect cells. Both AtXT1 and AtXT2 catalyzed the incorporation of xylosyl unit(s) onto all of these substrates, but with various efficiencies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)