Structural analyses of two arabinose containing oligosaccharides derived from olive fruit xyloglucan: XXSG and XLSG

Xyloglucan oligosaccharides were prepared by endo-(1 -->4)-beta -D-glucanas e digestion of alkali-extractable xyloglucan from olive fruit and purified by a combination of gel-permeation (Bio-Gel P-2) chromatography and high-pe rformance anion-exchange chromatography. The two most abundant oligosacchar ides were converted to the corresponding oligoglycosyl alditols by borohydr ide reduction and structurally characterised by NMR spectroscopy and post-s ource decay (PSD) fragment analysis of matrix-assisted laserinduced desorpt ion/ionisation time-of-flight (MALDI-TOF) mass spectra. The results reveale d that olive fruit xyloglucan is mainly built from two novel oligosaccharid es: XXSG and XLSG. The structure of the oligosaccharides confirmed the pres ence of a specific xyloglucan in olive fruit with alpha -L-Araf-(1 --> 2)-a lpha -D-Xylp sidechains as was suggested previously. The presence of such s idechains is a common feature of xyloglucans with an XXGG core produced by solanaceous plants but has not been demonstrated for other dicotyledonous p lants, which have in general an XXXG core. Direct treatment of cell wall ma terial from olive fruit with pectin degrading enzymes in combination with e ndo-(1 --> 4)-beta -D-glucanase revealed that some of the arabinose residue s of the oligosaccharides XXSG and XLSG are substituted with either 1 or 2 O-acetyl groups. (C) 2001 Elsevier Science Ltd. All rights reserved.