Substrate subsite recognition of the xyloglucan endo-transglycosylase or xyloglucan-specific endo-(1->4)-beta-D-glucanase from the cotyledons of germinated nasturtium (Tropaeolum majus L) seeds

We have investigated recognition requirement transglycosylase/xyloglucan-specific endo-(1 --> 4)-beta-D-glucanase (NXET) from the cotyledons of nasturtium seedlings. Seed xyloglucans are composed almost entirely of the Glc, subunits XXXG, XLXG, XXLG and XLLG, where G represents an unsubstituted glucose residue, X a xylose-substituted glucose residue and L a galactosyl-xylose-substituted glucose residue. Thus in the xyloglucan sequence shown below, the xylose (Xyl) residues at the backbone glucose (Glc) residues numbered - 3, - 2, + 2 and + 3 may be galactose-substituted, and NXET cleaves between the unsubstituted glucose at - 1 and the xylose-substituted glucose at + 1, which never carries a galactosyl substituent