Structural highlights
Publication Abstract from PubMedThe desire for improved methods of biomass conversion to fuels and feedstocks has re-awakened interest in the enzymology of plant cell wall degradation. The complex polysaccharide xyloglucan is abundant in plant matter, where it may account for up to 20% of the total primary cell wall carbohydrates. Despite this, few studies have focussed on xyloglucan saccharification, which requires a consortium of enzymes including endo-xyloglucanases, alpha-xylosidases, betagalactosidases and alpha-l-fucosidases, among others. Here, we present the characterisation of Xyl31A, a key alpha-xylosidase in xyloglucan utilisation by the model Gram-negative soil saprophyte Cellvibrio japonicus. CjXyl31A exhibits high regiospecificity for the hydrolysis xylogluco-oligosaccharides, with a particular preference for longer substrates. Crystallographic structures of both the apo enzyme and the trapped covalent 5-fluoro-beta-xylosyl-enzyme intermediate, together with docking studies with the XXXG heptasaccharide, revealed, for the first time in glycoside hydrolase family 31, the importance of a PA14 domain insert in the recognition of longer oligosaccharides by extension of the active site pocket. The observation that CjXyl31A was localised to the outer membrane provided support for a biological model of xyloglucan utilisation by C. japonicus, in which xylogluco-oligosaccharides generated by the action of a secreted endo-xyloglucanase are ultimately degraded in close proximity to the cell surface. Moreover, this study diversifies the toolbox of glycosidases for the specific modification and saccharification of cell wall polymers for biotechnological applications. Structural and enzymatic characterisation of a Glycoside Hydrolase Family 31 alphaxylosidase from Cellvibrio japonicus involved in xyloglucan saccharification.,Larsbrink J, Izumi A, Ibatullin F, Nakhai A, Gilbert HJ, Davies GJ, Brumer H Biochem J. 2011 Mar 22. PMID:21426303[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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