Abstract
Cellulose is an economically important material, but routes of its industrial processing have not been fully explored. The plant cell wall – the major source of cellulose – harbours enzymes of the xyloglucan endotransglucosylase/hydrolase (XTH) family. This class of enzymes is unique in that it is capable of elongating polysaccharide chains without the requirement for activated nucleotide sugars (e.g., UDP-glucose) and in seamlessly splitting and reconnecting chains of xyloglucan, a naturally occurring soluble analogue of cellulose. Here, we show that a recombinant version of AtXTH3, a thus far uncharacterized member of the Arabidopsis XTH family, catalysed the transglycosylation between cellulose and cello-oligosaccharide, between cellulose and xyloglucan-oligosaccharide, and between xyloglucan and xyloglucan-oligosaccharide, with the highest reaction rate observed for the latter reaction. In addition, this enzyme formed cellulose-like insoluble material from a soluble cello-oligosaccharide in the absence of additional substrates. This newly found activity (designated “cellulose endotransglucosylase,” or CET) can potentially be involved in the formation of covalent linkages between cellulose microfibrils in the plant cell wall. It can also comprise a new route of industrial cellulose functionalization.
Highlights
Cellulose is an economically important material, but routes of its industrial processing have not been fully explored
To estimate evolutionary history of the xyloglucan endotransglucosylase/hydrolase (XTH) family in land plants, we used protein sequences of all (33) XTHs identified in the genome of Arabidopsis thaliana; the sequence of barleyHvXET5, horsetail EfHTG, and poplar PtEG16; and some of their BLAST best hits from the wild grass (Brachypodium distachyon) and moss (Physcomitrella patens) genomes to construct a maximum-likelihood phylogenetic tree (Supplementary Fig. S1)
Our results demonstrate that AtXTH3 cleaves the β- 1,4-glucosidic linkage in amorphous cellulose and ligates the nascent reducing end to a non-reducing terminus of either cellulosic or xyloglucan oligosaccharide
Summary
Cellulose is an economically important material, but routes of its industrial processing have not been fully explored. We show that a recombinant version of AtXTH3, a far uncharacterized member of the Arabidopsis XTH family, catalysed the transglycosylation between cellulose and cellooligosaccharide, between cellulose and xyloglucan-oligosaccharide, and between xyloglucan and xyloglucan-oligosaccharide, with the highest reaction rate observed for the latter reaction This enzyme formed cellulose-like insoluble material from a soluble cello-oligosaccharide in the absence of additional substrates. This newly found activity (designated “cellulose endotransglucosylase,” or CET) can potentially be involved in the formation of covalent linkages between cellulose microfibrils in the plant cell wall. Land plant genomes generally encode ~30 members of the XTH family[15]
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