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Sökning: WFRF:(Abou Hachem Maher)

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1.
  • Abou-Hachem, Maher, et al. (författare)
  • Calcium binding and thermostability of carbohydrate binding module CBM4-2 of Xyn10A from Rhodothermus marinus.
  • 2002
  • Ingår i: Biochemistry. - : The American Chemical Society (ACS). - 0006-2960. ; 41:18, s. 5720-5729
  • Tidskriftsartikel (refereegranskat)abstract
    • Calcium binding to carbohydrate binding module CBM4-2 of xylanase 10A (Xyn10A) from Rhodothermus marinus was explored using calorimetry, NMR, fluorescence, and absorbance spectroscopy. CBM4-2 binds two calcium ions, one with moderate affinity and one with extremely high affinity. The moderate-affinity site has an association constant of (1.3 +/- 0.3) x 10(5) M(-1) and a binding enthalpy DeltaH(a) of -9.3 +/- 0.4 kJ x mol(-1), while the high-affinity site has an association constant of approximately 10(10) M(-1) and a binding enthalpy DeltaH(a) of -40.5 +/- 0.5 kJ x mol(-1). The locations of the binding sites have been identified by NMR and structural homology, and were verified by site-directed mutagenesis. The high-affinity site consists of the side chains of E11 and D160 and backbone carbonyls of E52 and K55, while the moderate-affinity site comprises the side chain of D29 and backbone carbonyls of L21, A22, V25, and W28. The high-affinity site is in a position analogous to the calcium site in CBM4 structures and in a recent CBM22 structure. Binding of calcium increases the unfolding temperature of the protein (T(m)) by approximately 23 degrees C at pH 7.5. No correlation between binding affinity and T(m) change was noted, as each of the two calcium ions contributes almost equally to the increase in unfolding temperature.
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2.
  • Abou Hachem, Maher, et al. (författare)
  • Carbohydrate-binding modules from a thermostable Rhodothermus marinus xylanase : Cloning, expression and binding studies
  • 2000
  • Ingår i: Biochemical Journal. - : Portland Press. - 0264-6021. ; 345:1, s. 53-60
  • Tidskriftsartikel (refereegranskat)abstract
    • The two N-terminally repeated carbohydrate-binding modules (CBM4-1 and CBM4-2) encoded by xyn10A from Rhodothermus marinus were produced in Escherichia coli and purified by affinity chromatography. Binding assays to insoluble polysaccharides showed binding to insoluble xylan and to phosphoric-acid-swollen cellulose but not to Avicel or crystalline cellulose. Binding to insoluble substrates was significantly enhanced by the presence of Na+ and Ca2+ ions. The binding affinities for soluble polysaccharides were tested by affinity electrophoresis; strong binding occurred with different xylans and β-glucan. CBM4-2 displayed a somewhat higher binding affinity than CBM4-1 for both soluble and insoluble substrates but both had similar specificities. Binding to short oligosaccharides was measured by NMR; both modules bound with similar affinities. The binding of the modules was shown to be dominated by enthalpic forces. The binding modules did not contribute with any significant synergistic effects on xylan hydrolysis when incubated with a Xyn10A catalytic module. This is the first report of family 4 CBMs with affinity for both insoluble xylan and amorphous cellulose.
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3.
  • Abou-Hachem, Maher (författare)
  • Glycoside hydrolases from Rhodothermus marinus Modular organisation and structure-function relationships
  • 2003
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The thermophilic bacterium Rhodothermus marinus produces several thermostable glycoside hydrolases. The studies presented in this thesis were performed on two enzymes, belonging to glycoside hydrolase families 10 and 12, produced by this microorganism. The family 10 xylanase, Xyn10A, is modular in architecture consisting of five domains or modules. The two isolated N-terminal modules were produced and characterised. These modules were proven to be carbohydrate-binding modules (CBMs) belonging to a novel subdivision of family 4 CBMs. Both modules display affinity for xylans, b-glucans, and to a less extent non-crystalline cellulose. The structure of the second of these binding modules (CBM4-2), solved by NMR, featured a b-sandwich with jelly roll-topology. Structural details and substrate titrations provided valuable insight on the determinants of specificity of the module. Both the Xyn10A CBMs and the third domain in the enzyme were shown to bind calcium ions, which had a pronounced effect on their thermostabilities. In addition, modular interactions seemed to enhance the stability of the enzyme, since deletion mutants were less stable than the full-length enzyme. No specific function could be ascribed the third domain of Xyn10A, while evidence suggested that the fifth domain is a novel module type that mediates cell-attachment. The primary structure of the family 12 endoglucanase Cel12A was analysed. These analyses showed that the catalytic module of this enzyme is preceded by a linker sequence and a putative signal peptide that destabilised the enzyme and impaired its expression in Escherichia coli. Designing mutants lacking this signal peptide readily solved the stability and production problems and these mutants retained their thermostability and activity. Finally, fusion proteins between the Xyn10A CBMs and the catalytic module of Cel12A were produced and some of their properties are reported.
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4.
  • Abou-Hachem, Maher, et al. (författare)
  • Probing stability of the modular thermostable xylanase Xyn10A
  • 2003
  • Ingår i: Extremophiles. - : Springer. - 1433-4909. ; 7:6, s. 483-491
  • Tidskriftsartikel (refereegranskat)abstract
    • The thermophilic bacterium Rhodothermus marinus produces a modular xylanase (Xyn10A) consisting of two N-terminal carbohydrate-binding modules (CBMs), followed by a domain of unknown function, and a catalytic module flanked by a fifth domain. Both Xyn10A CBMs bind calcium ions, and this study explores the effect of these ions on the stability of the full-length enzyme. Xyn10A and truncated forms thereof were produced and their thermostabilities were evaluated under different calcium loads. Studies performed using differential scanning calorimetry showed that the unfolding temperature of the Xyn10A was significantly dependent on the presence of Ca2+, and that the third domain of the enzyme binds at least one Ca2+. Thermal inactivation studies confirmed the role of tightly bound Ca2+ in stabilizing the enzyme, but showed that the presence of a large excess of this ion results in reduced kinetic stability. The truncated forms of Xyn10A were less stable than the full-length enzyme, indicative of module/domain thermostabilizing interactions. Finally, possible roles of the two domains of unknown function are discussed in the light of this study. This is the first report on the thermostabilizing role of calcium on a modular family 10 xylanase that displays multiple calcium binding in three of its five domains/modules.
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5.
  • Abou-Hachem, Maher, et al. (författare)
  • The modular organisation and stability of a thermostable family 10 xylanase
  • 2003
  • Ingår i: Biocatalysis and Biotransformation. - : Taylor & Francis. - 1024-2422. ; 21:5-6, s. 253-260
  • Tidskriftsartikel (refereegranskat)abstract
    • The thermophilic marine bacterium Rhodothermus marinus produces a modular family 10 xylanase (Xyn10A). It consists of two N-terminal family 4 carbohydrate binding modules (CBMs) followed by a domain of unknown function (D3), and a catalytic module (CM) flanked by a small fifth domain (D5) at its C-terminus. Several truncated mutants of the enzyme have been produced and characterised with respect to biochemical properties and stability. Multiple calcium binding sites are shown to be present in the two N-terminal CBMs and recent evidence suggests that the third domain of the enzyme also has the ability to bind the same metal ligand. The specific binding of Ca2+ was demonstrated to have a pronounced effect on thermostability as shown by differential scanning calorimetry and thermal inactivation studies. Furthermore, deletion mutants of the enzyme were less stable than the full-length enzyme suggesting that module interactions contributed to the stability of the enzyme. Finally, recent evidence indicates that the fifth domain of Xyn10A is a novel type of module mediating cell-attachment.
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6.
  • Ejby, Morten, et al. (författare)
  • 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
  • Ingår i: Journal of Biological Chemistry. - : ASBMB. - 0021-9258. ; 291:38, s. 20220-20231
  • 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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7.
  • Ejby, Morten, et al. (författare)
  • Structural basis for arabinoxylo-oligosaccharide capture by the probiotic Bifidobacterium animalis subsp lactis Bl-04
  • 2013
  • Ingår i: Molecular Microbiology. - : Wiley-Blackwell. - 1365-2958. ; 90:5, s. 1100-1112
  • Tidskriftsartikel (refereegranskat)abstract
    • Glycan utilization plays a key role in modulating the composition of the gut microbiota, but molecular insight into oligosaccharide uptake by this microbial community is lacking. Arabinoxylo-oligosaccharides (AXOS) are abundant in the diet, and are selectively fermented by probiotic bifidobacteria in the colon. Here we show how selectivity for AXOS uptake is established by the probiotic strain Bifidobacterium animalis subsp. lactisBl-04. The binding protein BlAXBP, which is associated with an ATP-binding cassette (ABC) transporter that mediates the uptake of AXOS, displays an exceptionally broad specificity for arabinosyl-decorated and undecorated xylo-oligosaccharides, with preference for tri- and tetra-saccharides. Crystal structures of BlAXBP in complex with four different ligands revealed the basis for this versatility. Uniquely, the protein was able to recognize oligosaccharides in two opposite orientations, which facilitates the optimization of interactions with the various ligands. Broad substrate specificity was further enhanced by a spacious binding pocket accommodating decorations at different mainchain positions and conformational flexibility of a lid-like loop. Phylogenetic and genetic analyses show that BlAXBP is highly conserved within Bifidobacterium, but is lacking in other gut microbiota members. These data indicate niche adaptation within Bifidobacterium and highlight the metabolic syntrophy (cross-feeding) among the gut microbiota.
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8.
  • Ejby, Morten, et al. (författare)
  • Structural basis for arabinoxylo-oligosaccharide capture by the probiotic Bifidobacterium animalis subsp lactis Bl-04
  • 2012
  • Ingår i: Journal of Psychopharmacology. - : SAGE Publications. - 1461-7285. ; 26:11, s. 1100-1112
  • Tidskriftsartikel (refereegranskat)abstract
    • Glycan utilization plays a key role in modulating the composition of the gut microbiota, but molecular insight into oligosaccharide uptake by this microbial community is lacking. Arabinoxylo-oligosaccharides (AXOS) are abundant in the diet, and are selectively fermented by probiotic bifidobacteria in the colon. Here we show how selectivity for AXOS uptake is established by the probiotic strain Bifidobacterium animalis subsp. lactisBl-04. The binding protein BlAXBP, which is associated with an ATP-binding cassette (ABC) transporter that mediates the uptake of AXOS, displays an exceptionally broad specificity for arabinosyl-decorated and undecorated xylo-oligosaccharides, with preference for tri- and tetra-saccharides. Crystal structures of BlAXBP in complex with four different ligands revealed the basis for this versatility. Uniquely, the protein was able to recognize oligosaccharides in two opposite orientations, which facilitates the optimization of interactions with the various ligands. Broad substrate specificity was further enhanced by a spacious binding pocket accommodating decorations at different mainchain positions and conformational flexibility of a lid-like loop. Phylogenetic and genetic analyses show that BlAXBP is highly conserved within Bifidobacterium, but is lacking in other gut microbiota members. These data indicate niche adaptation within Bifidobacterium and highlight the metabolic syntrophy (cross-feeding) among the gut microbiota.
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9.
  • Haddad Momeni, Majid, et al. (författare)
  • A novel starch-binding laccase from the wheat pathogen Zymoseptoria tritici highlights the functional diversity of ascomycete laccases
  • 2019
  • Ingår i: BMC Biotechnology. - : BioMed Central (BMC). - 1472-6750. ; 19
  • 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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  • Resultat 1-10 av 17
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