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|Title:||A barley xyloglucan xyloglucosyl transferase covalently links xyloglucan, cellulosic substrates, and (1 3;1 4)-β-D-glucans|
|Other Titles:||A barley xyloglucan xyloglucosyl transferase covalently links xyloglucan, cellulosic substrates, and (1 3;1 4)-beta-D-glucans|
|Citation:||Journal of Biological Chemistry, 2007; 282(17):12951-12962|
|Publisher:||Amer Soc Biochemistry Molecular Biology Inc|
|Maria Hrmova, Vladimir Farkas, Jelle Lahnstein, and Geoffrey B. Fincher|
|Abstract:||Molecular interactions between wall polysaccharides, which include cellulose and a range of noncellulosic polysaccharides such as xyloglucans and (1,3;1,4)-β-d-glucans, are fundamental to cell wall properties. These interactions have been assumed to be noncovalent in nature in most cases. Here we show that a highly purified barley xyloglucan xyloglucosyl transferase HvXET5 (EC 184.108.40.206), a member of the GH16 group of glycoside hydrolases, catalyzes the in vitro formation of covalent linkages between xyloglucans and cellulosic substrates and between xyloglucans and (1,3;1,4)-β-d-glucans. The rate of covalent bond formation catalyzed by HvXET5 with hydroxyethylcellulose (HEC) is comparable with that on tamarind xyloglucan, whereas that with (1,3; 1,4)-β-d-glucan is significant but slower. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric analyses showed that oligosaccharides released from the fluorescent HEC:xyloglucan conjugate by a specific (1,4)-β-dglucan 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)-β-d-glucan:xyloglucan conjugate by a specific (1,3;1,4)-β-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 xyloglucan endo-transglucosylases could link different polysaccharides in vivo and hence influence cell wall strength, flexibility, and porosity.|
|Keywords:||Cell Wall; Hordeum; Glucans; Cellulose; Glycosyltransferases; Xylans; Plant Proteins; Porosity|
|Rights:||Copyright © 2007 by the American Society for Biochemistry and Molecular Biology|
|Appears in Collections:||Agriculture, Food and Wine publications|
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