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      A β‐mannan utilization locus in Bacteroides ovatus involves a GH36 α‐galactosidase active on galactomannans

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          Abstract

          The Bacova_02091 gene in the β‐mannan utilization locus of Bacteroides ovatus encodes a family GH36 α‐galactosidase (BoGal36A), transcriptionally upregulated during growth on galactomannan. Characterization of recombinant BoGal36A reveals unique properties compared to other GH36 α‐galactosidases, which preferentially hydrolyse terminal α‐galactose in raffinose family oligosaccharides. BoGal36A prefers hydrolysing internal galactose substitutions from intact and depolymerized galactomannan. BoGal36A efficiently releases (> 90%) galactose from guar and locust bean galactomannans, resulting in precipitation of the polysaccharides. As compared to other GH36 structures, the BoGal36A 3D model displays a loop deletion, resulting in a wider active site cleft which likely can accommodate a galactose‐substituted polymannose backbone.

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          Most cited references30

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          A discrete genetic locus confers xyloglucan metabolism in select human gut Bacteroidetes

          A well-balanced human diet includes a significant intake of non-starch polysaccharides, collectively termed “dietary fibre,” from the cell walls of diverse fruits and vegetables. 1 Due to a paucity of alimentary enzymes encoded by the human genome, 2 our ability to derive energy from dietary fibre depends on saccharification and fermentation of complex carbohydrates by the massive microbial community residing in our distal gut. 3,4 The xyloglucans (XyGs), in particular, are a ubiquitous family of highly branched plant cell wall polysaccharides 5,6 whose mechanism(s) of degradation in the human gut and consequent importance in nutrition was heretofore unknown. 1,7,8 Here, we demonstrate that a single, complex gene locus in Bacteroides ovatus confers xyloglucan catabolism in this common colonic symbiont. Through targeted gene disruption, biochemical analysis of all predicted glycoside hydrolases and carbohydrate-binding proteins, and three-dimensional structural determination of the vanguard endo-xyloglucanase, we reveal the molecular mechanisms through which XyGs are hydrolysed to component monosaccharides for further metabolism. We also observe that orthologous xyloglucan utilization loci (XyGULs) serve as genetic markers of xyloglucan catabolism in Bacteroidetes, that XyGULs are restricted to a limited number of phylogenetically diverse strains, and that XyGULs are ubiquitous in surveyed human metagenomes. Our findings reveal that the metabolism of even highly abundant components of dietary fibre may be mediated by niche species, which has immediate fundamental and practical implications for gut symbiont population ecology in the context of human diet, nutrition and health. 9–12
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            How the walls come crumbling down: recent structural biochemistry of plant polysaccharide degradation.

            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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              A review of the enzymatic hydrolysis of mannans and synergistic interactions between β-mannanase, β-mannosidase and α-galactosidase.

              Mannan is an important polysaccharide found in softwoods and many other plant sources. Mannans from various sources display large differences in composition, structure and complexity. To hydrolyse mannan into its monomer sugars requires a number of enzymes working in synergy. This review examines mannan structure and the enzymes required for its hydrolysis. Several studies have investigated the effect of supplementing β-mannanases with β-mannosidases and α-galactosidases in binary and ternary combinations. Synergistic enhancement of hydrolysis has been found in some, but not all cases. In the case of mannosidases, they sometimes display an anti-synergistic effect with mannanases, most likely due to competition for binding sites. Most importantly, in the case of α-galactosidases, the same enzyme from different families display differences in synergistic interactions due to different specificities. An improved understanding of enzyme interactions will aid in achieving enhanced hydrolysis of mannans and higher sugar yields. This review highlights areas which require further research in order to gain a better understanding of mannan hydrolysis and utilisation. Such knowledge is very important as this can be used in the optimisation of commercial or purified enzyme mixtures to improve the economic viability of the conversion of high mannan-containing biomass such as softwoods into fermentable sugars for bioethanol production.
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                Author and article information

                Journal
                FEBS Lett
                FEBS Lett
                10.1002/(ISSN)1873-3468
                FEB2
                Febs Letters
                John Wiley and Sons Inc. (Hoboken )
                0014-5793
                1873-3468
                28 June 2016
                July 2016
                : 590
                : 14 ( doiID: 10.1111/feb2.2016.590.issue-14 )
                : 2106-2118
                Affiliations
                [ 1 ] Department of Biochemistry and Structural BiologyLund University Sweden
                [ 2 ] Department of Microbiology and ImmunologyUniversity of Michigan Medical School Ann Arbor MIUSA
                Author notes
                [*] [* ] Correspondence

                H. Stålbrand, Department of Biochemistry and Structural Biology, Lund University, PO Box 124, S‐221 00 Lund, Sweden

                Fax: +46 46 222 4116

                Tel: +46 46 222 8202

                E‐mail: henrik.stalbrand@ 123456biochemistry.lu.se

                Article
                FEB212250
                10.1002/1873-3468.12250
                5094572
                27288925
                ef71e593-ffe1-4840-a5bc-df335e2d9090
                © 2016 The Authors. FEBS Letters published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 23 March 2016
                : 07 June 2016
                : 09 June 2016
                Page count
                Pages: 13
                Funding
                Funded by: Swedish Foundation for Strategic Research
                Award ID: RBP 14‐0046
                Funded by: Swedish Innovation Agency
                Award ID: 2013‐03024
                Funded by: Swedish Research Agency FORMAS
                Award ID: 213‐2014‐1254
                Categories
                Research Letter
                Research Letters
                Enzymology
                Custom metadata
                2.0
                feb212250
                July 2016
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.9.6 mode:remove_FC converted:03.11.2016

                Molecular biology
                bacteroides ovatus,galactomannan modification,gh36 α‐galactosidase,polysaccharide utilization locus

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