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Papers In Press, published online ahead of print February 28, 2007
Faculty of Sciences, University of Adelaide, Adelaide, SA 5064
Corresponding Author: maria.hrmova{at}adelaide.edu.au
Molecular interactions between wall polysaccharides, which include cellulose and a range of non-cellulosic polysaccharides such as xyloglucans and (1,3;1,4)-ß-D-glucans, are fundamental to cell wall properties. These interactions have been assumed to be non-covalent in nature in most cases. Here we show that a highly purified barley xyloglucan xyloglucosyl transferase HvXET5 (EC 2.4.1.207), a member of the GH16 group of glycoside hydrolases, catalyses the in vitro formation of covalent linkages between xyloglucans and cellulosic substrates, and between xyloglucans and (1,3;1,4)-ß-D-glucans. The rate of covalent bond formation catalyzed by HvXET5 with hydroxyethylcellulose (HEC) is comparable with that on tamarind xyloglucan, while that with (1,3;1,4)-ß-D-glucan is significant but slower. MALDI-TOF mass spectrometric analyses showed that oligosaccharides released from the fluorescent HEC:xyloglucan conjugate by a specific (1,4)-ß-D-glucan endohydrolase consisted of xyloglucan substrate with one, two or three glucosyl residues attached. Ancillary peaks contained hydroxyethyl substituents (m/z 45) and confirmed that the parent material consisted of HEC covalently linked with xyloglucan. Similarly, partial hydrolysis of the (1,3;1,4)-ß-D-glucan:xyloglucan conjugate by a specific (1,4;1,3)-ß-D-glucan endohydrolase revealed the presence of a series of fluorescent oligosaccharides that consisted of the fluorescent xyloglucan acceptor substrate linked covalently with 2-6 glucosyl residues. These findings raise the possibility that XETs could link different polysaccharides in vivo, and hence influence cell wall strength, flexibility and porosity.
J. Biol. Chem, 10.1074/jbc.M611487200
Submitted on December 15, 2006
Revised on February 27, 2007
Accepted on February 28, 2007
A barley xyloglucan xyloglucosyl transferase covalently links xyloglucan, cellulosic substrates and (1,3;1,4)-beta-D-glucans
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