A Barley xyloglucan xyloglucosyl transferase covalently links xyloglucan, cellulosic substrates, and (1,3;1,4)-beta-D-glucans.
Molecular interactions between wall polysaccharides, which include cellulose and a range of noncellulosic polysaccharides such as xyloglucans and (1,3;1,4)-beta-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 2.4.1.207), 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)-beta-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)-beta-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)-beta-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)-beta-D-glucan:xyloglucan conjugate by a specific (1,3;1,4)-beta-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.
Hrmova
Maria
M
School of Agriculture, Food and Wine, and Australian Centre for Plant Functional Genomics, University of Adelaide, Waite Campus, Glen Osmond, South Australia 5064, Australia. maria.hrmova@adelaide.edu.au
Farkas
Vladimir
V
Lahnstein
Jelle
J
Fincher
Geoffrey B
GB
D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism*; D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D005936:Glucans / Q000737:chemistry / Q000378:metabolism*; D016695:Glycosyltransferases / Q000737:chemistry / Q000378:metabolism*; D001467:Hordeum / Q000201:enzymology*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D016062:Porosity; D014990:Xylans / Q000737:chemistry / Q000378:metabolism*
D005936:Glucans; D010940:Plant Proteins; D014990:Xylans; C029353:xyloglucan; D002482:Cellulose; C002283:hydroxyethylcellulose; D016695:Glycosyltransferases; C473049:xyloglucan - xyloglucosyltransferase