| 1. |
- Cartmell, Alan, et al.
(författare)
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The structure and function of an arabinan-specific alpha-1,2-arabinofuranosidase identified from screening the activities of bacterial GH43 glycoside hydrolases
- 2011
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Ingår i: Journal of Biological Chemistry. - : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 286:17
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Tidskriftsartikel (refereegranskat)abstract
- Reflecting the diverse chemistry of plant cell walls, microorganisms that degrade these composite structures synthesize an array of glycoside hydrolases. These enzymes are organized into sequence-, mechanism-, and structure-based families. Genomic data have shown that several organisms that degrade the plant cell wall contain a large number of genes encoding family 43 (GH43) glycoside hydrolases. Here we report the biochemical properties of the GH43 enzymes of a saprophytic soil bacterium, Cellvibrio japonicus, and a human colonic symbiont, Bacteroides thetaiotaomicron. The data show that C. japonicus uses predominantly exo-acting enzymes to degrade arabinan into arabinose, whereas B. thetaiotaomicron deploys a combination of endo-and side chain-cleaving glycoside hydrolases. Both organisms, however, utilize an arabinan-specific alpha-1,2-arabinofuranosidase in the degradative process, an activity that has not previously been reported. The enzyme can cleave alpha-1,2-arabinofuranose decorations in single or double substitutions, the latter being recalcitrant to the action of other arabinofuranosidases. The crystal structure of the C. japonicus arabinan-specific alpha-1,2-arabinofuranosidase, CjAbf43A, displays a five-bladed beta-propeller fold. The specificity of the enzyme for arabinan is conferred by a surface cleft that is complementary to the helical backbone of the polysaccharide. The specificity of CjAbf43A for alpha-1,2-L-arabinofuranose side chains is conferred by a polar residue that orientates the arabinan backbone such that O2 arabinose decorations are directed into the active site pocket. A shelflike structure adjacent to the active site pocket accommodates O3 arabinose side chains, explaining how the enzyme can target O2 linkages that are components of single or double substitutions.
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| 2. |
- Larsbrink, Johan, et al.
(författare)
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Structural and enzymatic characterization of a glycoside hydrolase family 31 alpha-xylosidase from Cellvibrio japonicus involved in xyloglucan saccharification
- 2011
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 436, s. 567-580
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Tidskriftsartikel (refereegranskat)abstract
- The desire for improved methods of biomass conversion into 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 focused on xyloglucan saccharification, which requires a consortium of enzymes including endo-xyloglucanases, alpha-xylosidases, beta-galactosidases and alpha-L-fucosidases, among others. In the present paper, we show the characterization of Xy131A, a key alpha-xylosidase in xyloglucan utilization by the model Gram-negative soil saprophyte Cellvibrio japonicus. CjXy131A exhibits high regiospecificity for the hydrolysis of XGOs (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 GH31 (glycoside hydrolase family 31), the importance of PA14 domain insert in the recognition of longer oligosaccharides by extension of the active-site pocket. The observation that CjXy131A was localized to the outer membrane provided support for a biological model of xyloglucan utilization by C. japonicas, in which XGOs generated by the action of a secreted endo-xyloglucanase are ultimately degraded in close proximity to the cell surface. Moreover, the present study diversifies the toolbox of glycosidases for the specific modification and saccharification of cell wall polymers for biotechnological applications.
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| 3. |
- Gilbert, Harry J., et al.
(författare)
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How the walls come crumbling down : recent structural biochemistry of plant polysaccharide degradation
- 2008
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Ingår i: Current opinion in plant biology. - : Elsevier BV. - 1369-5266 .- 1879-0356. ; 11:3, s. 338-348
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Forskningsöversikt (refereegranskat)abstract
- The recent years have witnessed considerable developments in the interpretation of the three-dimensional structures of plant polysaccharide-degrading enzymes in the context of their functional specificity. A plethora of new structures of catalytic, carbohydrate-binding and protein-scaffolding modules involved in (hemi)cellulose catabolism has emerged in harness with sophisticated biochemical analysis. Despite significant advances, a full understanding of the intricacies of substrate recognition and catalysis by these diverse and specialised enzymes remains an important goal, especially if the application potential of these biocatalysts is to be fully realised.
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