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- Ejby, Morten, et al.
(författare)
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An atp binding cassette transporter mediates the uptake of α-(1,6)-linked dietary oligosaccharides in bifidobacterium and correlates with competitive growth on these substrates
- 2016
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Ingår i: Journal of Biological Chemistry. - 0021-9258. ; 291:38, s. 20220-20231
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Tidskriftsartikel (refereegranskat)abstract
- The molecular details and impact of oligosaccharide uptake by distinct human gut microbiota (HGM) are currently not well understood. Non-digestible dietary galacto- and gluco-α-(1,6)-oligosaccharides from legumes and starch, respectively, are preferentially fermented by mainly bifidobacteria and lactobacilli in the human gut. Here we show that the solute binding protein (BlG16BP) associated with an ATP binding cassette (ABC) transporter from the probiotic Bifidobacterium animalis subsp. lactis Bl-04 binds α-(1,6)-linked glucosides and galactosides of varying size, linkage, and monosaccharide composition with preference for the trisaccharides raffinose and panose. This preference is also reflected in the α-(1,6)-galactoside uptake profile of the bacterium. Structures of BlG16BP in complex with raffinose and panose revealed the basis for the remarkable ligand binding plasticity of BlG16BP, which recognizes the nonreducing α-(1,6)-diglycoside in its ligands. BlG16BP homologues occur predominantly in bifidobacteria and a few Firmicutes but lack in other HGMs. Among seven bifidobacterial taxa, only those possessing this transporter displayed growth on α-(1,6)-glycosides. Competition assays revealed that the dominant HGM commensal Bacteroides ovatus was out-competed by B. animalis subsp. lactis Bl-04 in mixed cultures growing on raffinose, the preferred ligand for the BlG16BP. By comparison, B. ovatus mono-cultures grew very efficiently on this trisaccharide These findings suggest that the ABC-mediated uptake of raffinose provides an important competitive advantage, particularly against dominant Bacteroides that lack glycan-specific ABC-transporters. This novel insight highlights the role of glycan transport in defining the metabolic specialization of gut bacteria.
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| 2. |
- Haddad Momeni, Majid, et al.
(författare)
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A novel starch-binding laccase from the wheat pathogen Zymoseptoria tritici highlights the functional diversity of ascomycete laccases
- 2019
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Ingår i: BMC Biotechnology. - : Springer Science and Business Media LLC. - 1472-6750. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- Background: Laccases are multicopper oxidases, which are assigned into auxiliary activity family 1 (AA1) in the CAZy database. These enzymes, catalyzing the oxidation of phenolic and nonphenolic substrates coupled to reduction of O2 to H2O, are increasingly attractive as eco-friendly oxidation biocatalysts. Basidiomycota laccases are well characterized due to their potential in de-lignification of lignocellulose. By contrast, insight into the biochemical diversity of Ascomycota counterparts from saprophytes and plant pathogens is scarce. Results: Here, we report the properties of the laccase from the major wheat pathogen Zymoseptoria tritici (ZtrLac1A), distinguished from common plant fungal pathogens by an apoplastic infection strategy. We demonstrate that ZtrLac1A is appended to a functional starch-binding module and displays an activity signature disfavoring relatively apolar phenolic redox mediators as compared to the related biochemically characterized laccases. By contrast, the redox potential of ZtrLac1A (370 mV vs. SHE) is similar to ascomycetes counterparts. The atypical specificity is consistent with distinctive sequence substitutions and insertions in loops flanking the T1 site and the enzyme C-terminus compared to characterized laccases. Conclusions: ZtrLac1A is the first reported modular laccase appended to a functional starch-specific carbohydrate binding module of family 20 (CBM20). The distinct specificity profile of ZtrLac1A correlates to structural differences in the active site region compared to previously described ascomycetes homologues. These differences are also highlighted by the clustering of the sequence of ZtrLac1A in a distinct clade populated predominantly by plant pathogens in the phylogenetic tree of AA1 laccases. The possible role of these laccases in vivo merits further investigations. These findings expand our toolbox of laccases for green oxidation and highlight the binding functionality of CBM-appended laccases as versatile immobilization tags.
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| 3. |
- Madsen, Jan Busk, et al.
(författare)
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Structural and Mechanical Properties of Thin Films of Bovine Submaxillary Mucin (BSM) vs. Porcine Gastric Mucin (PGM) on a Hydrophobic Surface in Aqueous Solutions
- 2016
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:38, s. 9687-9696
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Tidskriftsartikel (refereegranskat)abstract
- The structural and mechanical properties of thin films generated from two types of mucins, namely, bovine submaxillary mucin (BSM) and porcine gastric mucin (PGM) in aqueous environment were investigated with several bulk and surface analytical techniques. Both mucins generated hydrated films on hydrophobic polydimethylsiloxane (PDMS) surfaces from spontaneous adsorption arising from their amphiphilic characteristic. However, BSM formed more elastic films than PGM at neutral pH condition. This structural difference was manifested from the initial film formation processes to the responses to shear stresses applied to the films. Acidification of environmental pH led to strengthening the elastic character of BSM films with increased adsorbed mass, whereas an opposite trend was observed for PGM films. We propose that this contrast originates from that negatively charged motifs are present for both the central and terminal regions of BSM molecule, whereas a similar magnitude of negative charges is localized at the termini of PGM molecule. Given that hydrophobic motifs acting as an anchor are also localized in the terminal region, electrostatic repulsion between anchoring units of PGM molecules on a nonpolar PDMS surface leads to weakening of the mechanical integrity of the films.
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| 4. |
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| 5. |
- Teze, David, et al.
(författare)
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The catalytic acid-base in GH109 resides in a conserved GGHGG loop and allows for comparable α-retaining and β-inverting activity in an N-acetylgalactosaminidase from Akkermansia muciniphila
- 2019
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Ingår i: ChemRxiv. - : American Chemical Society (ACS).
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The study describes the first glycoside hydrolase that exhibits comparable levels of activity on α- and β-linked saccharide substrates. This enzyme, assigned into GH109, is encoded by the genome of the human gut symbiont Akkermansia muciniphila that is a model primary degrader of the heavily O-glycosylated mucin glycoprotein that coats the epithelial enterocytes.The elusive catalytic acid/base catalyst in GH109 enzymes is identified as a histidine that is presented by a flexible loop that positions it for catalysis on both α- and β-substrates. This dual activity may be an evolutionary adaptation to extend the range of substrates targeted by a single non-canonical NAD+-dependant GH.
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