Original Article

Planta

, 227:893

First online:

Anionic derivatives of xyloglucan function as acceptor but not donor substrates for xyloglucan endotransglucosylase activity

  • Takumi TakedaAffiliated withThe Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, School of Biological Sciences, The University of EdinburghIwate Biotechnology Research Center
  • , Janice G. MillerAffiliated withThe Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, School of Biological Sciences, The University of Edinburgh
  • , Stephen C. FryAffiliated withThe Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, School of Biological Sciences, The University of Edinburgh Email author 

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Abstract

Tamarind xyloglucan was oxidised by reaction with sodium hypochlorite in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO). Galactose residues and non-xylosylated glucose residues were thus converted into galacturonic and glucuronic acid residues, respectively, producing an anionic polysaccharide. Acid hydrolysis of oxidised xyloglucan yielded two aldobiouronic acids, deduced to be β-d-GalpA-(1→2)-d-Xyl and β-d-GlcpA-(1→4)-d-Glc. Anionic xyloglucan had a decreased ability to hydrogen-bond to cellulose and to complex with iodine. It was almost totally resistant to digestion by cellulase [endo-(1→4)-β-glucanase] and did not serve as a donor substrate for xyloglucan endotransglucosylase (XET) activity. Like several other anionic polysaccharides, it promoted XET activity when unmodified (non-ionic) xyloglucan was used as donor substrate. Anionic xyloglucan may mimic polyanions whose presence in the plant cell wall promotes the action of endogenous XTH proteins. NaOCl with TEMPO oxidised the heptasaccharide, XXXG, to form XXX-glucarate, which did serve as an acceptor substrate although at a rate approximately fourfold less than XXXG itself. Anionic derivatives of xyloglucan, acting as acceptor but not donor substrates, may be valuable tools for exploring the biological roles of XTHs in the integration versus the re-structuring of xyloglucan in the plant cell wall.

Keywords

Cell expansion Hemicellulose XET activity Transglycosylation Glucaric acid Xyloglucan oxidation