Characterization of seven xyloglucan oligosaccharides containing from seventeen to twenty glycosyl residues.
The complete primary structures of seven oligosaccharide subunits of the xyloglucan secreted by suspension-cultured Acer pseudoplatanus cells were determined. The oligosaccharides, ranging in size from 17 to 20 glycosyl residues, were generated by treatment of the xyloglucan with an endo-beta-(1----4)-glucanase. The oligosaccharide components of a fraction obtained by Bio-Gel P-2 chromatography of enzyme-treated xyloglucan were further purified by normal-phase h.p.l.c. and then converted to the corresponding oligoglycosyl alditols by reduction with NaBH4. The oligoglycosyl alditols, after purification to near homogeneity by reversed-phase h.p.l.c., were structurally characterized by 1H-n.m.r. spectroscopy, fast-atom bombardment mass spectrometry (f.a.b.-m.s.), and analysis of their glycosyl-residue and glycosyl-linkage compositions. Novel structural elements of xyloglucans were observed in this study, including beta-D-xylopyranosyl and alpha-L-arabinofuranosyl-(1----3)-beta-D-xylopyranosyl sidechains. The results also extend our list of correlations between 1H-n.m.r. resonances and specific structural features of xyloglucans and thus enhance our ability to determine the structures of xyloglucans from various sources.