Trans-alpha-xylosidase, a widespread enzyme activity in plants, introduces (1->4)-alpha-D-xylobiose side-chains into xyloglucan structures

Lenka Frankova, Stephen Fry

Research output: Contribution to journalArticlepeer-review

Abstract

Angiosperms possess a retaining trans--xylosidase activity that catalyses the inter-molecular transfer of xylose residues between xyloglucan structures. To identify the linkage of the newly transferred -xylose residue, we used [Xyl-3H]XXXG (xyloglucan heptasaccharide) as donor substrate and reductively-aminated xyloglucan oligosaccharides (XGO-NH2) as acceptor. Asparagus officinalis enzyme extracts generated cationic radioactive products ([3H]Xyl•XGO-NH2) that were Driselase-digestible to a neutral trisaccharide containing an -[3H]xylose residue. After borohydride reduction, the trimer exhibited high molybdate-affinity, indicating xylobiosyl-(16)-glucitol rather than a di-xylosylated glucitol. Thus the trans--xylosidase had grafted an additional -[3H]xylose residue onto the xylose of an isoprimeverose unit. The trisaccharide was rapidly acetolysed to an -[3H]xylobiose, confirming the presence of an acetolysis-labile (16)-bond. The -[3H]xylobiitol formed by reduction of this -[3H]xylobiose had low molybdate-affinity, indicating a (12) or (14) linkage. In NaOH, the -[3H]xylobiose underwent alkaline peeling at the moderate rate characteristic of a (14)-disaccharide. Finally, we synthesised eight non-radioactive xylobioses [ and ; (11), (12), (13) and (14)] and found that the [3H]xylobiose co-chromatographed only with (14)--xylobiose. We conclude that Asparagus trans--xylosidase activity generates a novel xyloglucan building block, -D-Xylp-(14)--D-Xylp-(16)-D-Glc (abbreviation: ‘V’). Modifying xyloglucan structures in this way may alter oligosaccharin activities, or change their suitability as acceptor substrates for xyloglucan endotransglucosylase (XET) activity.
Original languageEnglish
Pages (from-to)29-43
Number of pages15
JournalPhytochemistry
Volume78
Issue number1
Early online date16 Mar 2012
DOIs
Publication statusPublished - 30 Jun 2012

Keywords

  • Molybdate electrophoresis
  • Oligosaccharins
  • Radiolabelling
  • Trans-alpha-xylosidase
  • Transglycosylation
  • Xylobioses
  • Xyloglucan

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