Xyloglucan endotransglycosylase, a new wall-loosening enzyme activity from plants

Xyloglucan endotransglycosylase, a new wall-loosening enzyme activity from plants

1. Cell-free extracts of all plants tested contained a novel enzyme activity (xyloglucan endotransglycosylase, XET) able to transfer a high-M(r) portion from a donor xyloglucan to a suitable acceptor such as a xyloglucan-derived nonasaccharide (Glc(4)Xyl(3)GalFuc; XG9). 2. A simple assay for the enz...

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Bibliographic Details
Published in:Biochemical journal Vol. 282; no. 3; pp. 821 - 828
Main Authors: Fry, S.C, Smith, R.C, Renwick, K.F, Martin, D.J, Hodge, S.K, Matthews, K.J
Format: Journal Article
Language:English
Published: Colchester Portland Press 15-03-1992
Subjects:
Analytical, structural and metabolic biochemistry
Biological and medical sciences
Bryopsida
Carbohydrate Sequence
cell growth
Cell Wall - enzymology
cell wall components
Cellulase - metabolism
cellulases
characterization
endotransglycosylation
enzyme activity
enzymes
Enzymes and enzyme inhibitors
Fabaceae - enzymology
Fundamental and applied biological sciences. Psychology
Glucans
Glycosyltransferases - metabolism
Liliopsida
Magnoliopsida
Miscellaneous
Molecular Sequence Data
Plant Development
Plant Proteins - metabolism
Plants - enzymology
Plants, Medicinal
Polysaccharides - metabolism
Substrate Specificity
substrate specifiicity
substrates
Xylans
xyloglucans
Plant
Enzymatic activity
Activator
Substrate specificity
Enzyme inhibitor
Polysaccharide
Physicochemical properties
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Summary:1. Cell-free extracts of all plants tested contained a novel enzyme activity (xyloglucan endotransglycosylase, XET) able to transfer a high-M(r) portion from a donor xyloglucan to a suitable acceptor such as a xyloglucan-derived nonasaccharide (Glc(4)Xyl(3)GalFuc; XG9). 2. A simple assay for the enzyme, using [3H]XG9 and based on the ability of the [3H]polysaccharide product to bind to filter paper, is described. 3. The enzyme was highly specific for xyloglucan as the glycosyl donor, and showed negligible transglycosylation of other polysaccharides, including CM-cellulose. 4. The Km for XG9 was 50 micromolar; certain other 3H-labelled xyloglucan oligosaccharides also acted as acceptors, and certain nonradioactive xyloglucan oligosaccharides competed with [3H]XG9 as acceptor; the minimum acceptor structure was deduced to be... 5. The pH optimum was approx. 5.5 and the enzyme was less than half as active at pH 7.0. The enzyme was slightly activated by Ca(2+), Mg(2+), Mn(2+), spermidine, ascorbate and 2-mercaptoethanol, and inhibited by Ag+, Hg(2+), Zn(2+) and La(3+). 6. XET activity was essentially completely extracted by aqueous solutions of low ionic strength; Triton X-100, Ca(2+), La(3+), and Li+ did not enhance extraction. Negligible activity was left in the unextractable (cell-wall-rich) residue. 7. The enzyme differed from the major cellulases (EC 3.2.1.4) of pea in: (a) susceptibility to inhibition by cello-oligosaccharides, (b) polysaccharide substrate specificity, (c) inducibility by auxin, (d) requirement for salt in the extraction buffer and (e) activation by 2-mercaptoethanol. XET is therefore concluded to be a new enzyme activity (xyloglucan:xyloglucan xyloglucanotransferase; EC 2.4.1.-). 8. XET was detected in extracts of the growing portions of dicotyledons, monocotyledons (graminaceous and liliaceous) and bryophytes. 9. The activity was positively correlated with growth rate in different zones of the pea stem. 10. We propose that XET is responsible for cutting and rejoining intermicrofibrillar xyloglucan chains and that it thus causes the wall-loosening required for plant cell expansion.
ISSN:0264-6021
1470-8728
DOI:10.1042/bj2820821