The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ken Izumori - One of the best experts on this subject based on the ideXlab platform.
-
green syntheses of new 2 c methyl aldohexoses and 5 c methyl Ketohexoses d tagatose 3 epimerase dte a promiscuous enzyme
Tetrahedron-asymmetry, 2008Co-Authors: Nigel A Jones, Kenji Morimoto, Devendar Rao, Akihide Yoshihara, Pushpakiran Gullapalli, Goro Takata, Stuart J Hunter, Mark R Wormald, Raymond A Dwek, Ken IzumoriAbstract:Abstract The Kiliani synthesis on the 4 readily accessible Ketohexoses ( d -fructose, d -tagatose, l -sorbose, d -psicose) allows access to 4 diastereomeric 2-C-methyl-aldohexoses (2-C-methyl- d -mannose, 2-C-methyl- d -talose, 2-C-methyl- l -gulose, 2-C-methyl- d -allose) and 4 diastereomeric 2-C-methyl-alditols (2-C-methyl- d -mannitol, 2-C-methyl- d -talitol, 2-C-methyl- l -gulitol, 2-C-methyl- d -allitol). Microbial oxidation of 2-C-methyl- d -mannitol and 2-C-methyl- l -gulitol gave 5-C-methyl- d -fructose; microbial oxidation of 2-C-methyl- d -talitol afforded 5-C-methyl- d -psicose, whereas 2-C-methyl- d -allitol formed 5-C-methyl- l -psicose. Both enantiomers of 5-C-methyl-fructose were equilibrated by d -tagatose-3-epimerase (DTE) with both enantiomers of 5-C-methyl-psicose. These transformations demonstrate that polyol dehydrogenases and DTE act on branched synthetic sugars. Full NMR analyses show that 5-C-methyl- d -fructose is present as the β-pyranose and β-furanose forms in a ratio of 90:10; all pyranose and furanose forms of 5-C-methyl- d -psicose are present in solution. The combination of chemical and biological procedures allows the environmentally friendly generation of a new family of branched monosaccharides.
-
Izumoring: A strategy for bioproduction of all hexoses
Journal of Biotechnology, 2006Co-Authors: Ken IzumoriAbstract:Izumoring is a new concept for the bioproduction of all hexose sugars - 16 aldohexoses, eight Ketohexoses and 10 hexitols -- using enzymatic and microbiological reactions. The biocatalysts necessary for the strategy were (i) d-tagatose 3-epimerase [which epimerizes all Ketohexoses at C-3 of the sugar], (ii) polyol dehydrogenases [which catalyze oxidation-reduction reactions between Ketohexoses and the corresponding hexitols], and (iii) aldose isomerases [which catalyze isomerization reactions between aldohexoses and corresponding aldoketoses]. All Ketohexoses, aldohexoses and hexitols may be arranged in a symmetric ring connected by the biochemical reactions, allowing the design for the bioproduction of all 34 hexose sugars. The ring shows there are four entrances to the l-hexose world from the natural d-hexoses. The Izumoring ring shows clearly the relationship and the position of all 34 six carbon sugars.
-
kiliani reactions on ketoses branched carbohydrate building blocks from d tagatose and d psicose
Tetrahedron Letters, 2005Co-Authors: Raquel G Soengas, Michela I Simone, David J Watkin, Ulla P Skytte, Wim Soetaert, Ken Izumori, George W J FleetAbstract:Abstract D -Tagatose and D -psicose on treatment with sodium cyanide gave mixtures of branched sugar lactones; extraction of the crude products by acetone in the presence of acid permits direct access to branched carbohydrate diacetonides, likely to be of value as new chirons. In both cases, the major lactone products—diacetonides with a 2,3- cis -diol relationship—can be crystallised in around 40–50% yield from the Ketohexose. A practical procedure for the conversion of 30 g of D -tagatose to give 24 g of 2,3:5,6-di- O -isopropylidene-2- C -hydroxymethyl- D -talono-1,4-lactone is reported.
-
novel reactions of l rhamnose isomerase from pseudomonas stutzeri and its relation with d xylose isomerase via substrate specificity
Biochimica et Biophysica Acta, 2004Co-Authors: Khim Leang, Tom Granstrom, Kenji Morimoto, Goro Takada, Yoshinori Fukai, Ken IzumoriAbstract:Escherichia coli strain JM 109 harboring 6 x His-tag L-rhamnose isomerase (L-RhI) from Pseudomonas stutzeri allowed a 20-fold increase in the volumetric yield of soluble enzyme compared to the value for the intrinsic yield. Detailed studies on the substrate specificity of the purified His-tagged protein revealed that it catalyzed previously unknown common and rare aldo/ketotetrose, aldo/ketopentose, and aldo/Ketohexose substrates in both D- and L-forms, for instance, erythrose, threose, xylose, lyxose, ribose, glucose, mannose, galactose, altrose, tagatose, sorbose, psicose, and fructose. Using a high enzyme-substrate ratio in extended reactions, the enzyme-catalyzed interconversion reactions from which two different products from one substrate were formed: L-lyxose, L-glucose, L-tagatose and D-allose were isomerized to L-xylulose and L-xylose, L-fructose and L-mannose, L-galactose and L-talose, and D-psicose and D-altrose, in that order. Kinetic studies, however, showed that L-rhamnose with Km and Vmax values of 11 mM and 240 U/mg, respectively, was the most preferred substrate, followed by L-mannose, L-lyxose, D-ribose, and D-allose. Based on the observed catalytic mode of action, these new findings reflected a hitherto undetected interrelation between L-RhI and D-xylose isomerase (D-XI).
-
modification of ovalbumin with a rare Ketohexose through the maillard reaction effect on protein structure and gel properties
Journal of Agricultural and Food Chemistry, 2004Co-Authors: Yuanxia Sun, Shigeru Hayakawa, Ken IzumoriAbstract:The effect of nonenzymatic glycation on the structural changes and gelling properties of hen ovalbumin (OVA) through the Maillard reaction was studied. OVA was incubated at the dry state with a rare Ketohexose (D-psicose, Psi) and two alimentary sugars (D-fructose, Fru; D-glucose, Glc) at 55 degrees C and 65% relative humidity. To evaluate the modification of OVA by different reducing sugars during the glycation process, the extent of the Maillard reaction, aggregation processes, structural changes, and gelling behaviors were investigated. Reactivity of Psi with the protein amino groups was much lower than that of both Fru and Glc, whereas Psi induced production of browning and fluorescent substances more strongly than the two alimentary sugars did. Furthermore, OVA showed an increased tendency toward multimeric aggregation upon modifying with Psi through covalent bond. The modified OVAs with reducing sugar were similar to nonglycated control sample in Fourier transform infrared (FT-IR) characteristics, but significantly decreased in intensity of tryptophan-related fluorescence. The results indicate that although glycation brought about similar changes in the secondary structure without great disruption of native structure, its influence on the side chains of protein in tertiary structure could be different. Breaking strength of heat-induced glycated OVA gels with Psi was markedly enhanced by the Maillard reaction. These results suggest that Psi had a strong cross-linking activity with OVA; consequently, the glycated OVA with Psi could improve gelling properties under certain controlled conditions.
Robert H. White - One of the best experts on this subject based on the ideXlab platform.
-
l aspartate semialdehyde and a 6 deoxy 5 Ketohexose 1 phosphate are the precursors to the aromatic amino acids in methanocaldococcus jannaschii
Biochemistry, 2004Co-Authors: Robert H. WhiteAbstract:No orthologs are present in the genomes of the archaea encoding genes for the first two steps in the biosynthesis of the aromatic amino acids leading to 3-dehydroquinate (DHQ). The absence of these genes prompted me to examine the nature of the reactions involved in the archaeal pathway leading to DHQ in Methanocaldococcus jannaschii. Here I report that 6-deoxy-5-ketofructose 1-phosphate and l-aspartate semialdehyde are precursors to DHQ. The sugar, which is derived from glucose 6-P, supplies a “hydroxyacetone” fragment, which, via a transaldolase reaction, undergoes an aldol condensation with the l-aspartate semialdehyde to form 2-amino-3,7-dideoxy-d-threo-hept-6-ulosonic acid. Despite the fact that both hydroxyacetone and hydroxyacetone-P were measured in the cell extracts and confirmed to arise from glucose 6-P, neither compound was found to serve as a precursor to DHQ. This amino sugar then undergoes a NAD dependent oxidative deamination to produce 3,7-dideoxy-d-threo-hept-2,6-diulosonic acid which cy...
-
l aspartate semialdehyde and a 6 deoxy 5 Ketohexose 1 phosphate are the precursors to the aromatic amino acids in methanocaldococcus jannaschii
Biochemistry, 2004Co-Authors: Robert H. WhiteAbstract:No orthologs are present in the genomes of the archaea encoding genes for the first two steps in the biosynthesis of the aromatic amino acids leading to 3-dehydroquinate (DHQ). The absence of these genes prompted me to examine the nature of the reactions involved in the archaeal pathway leading to DHQ in Methanocaldococcus jannaschii. Here I report that 6-deoxy-5-ketofructose 1-phosphate and l-aspartate semialdehyde are precursors to DHQ. The sugar, which is derived from glucose 6-P, supplies a "hydroxyacetone" fragment, which, via a transaldolase reaction, undergoes an aldol condensation with the l-aspartate semialdehyde to form 2-amino-3,7-dideoxy-D-threo-hept-6-ulosonic acid. Despite the fact that both hydroxyacetone and hydroxyacetone-P were measured in the cell extracts and confirmed to arise from glucose 6-P, neither compound was found to serve as a precursor to DHQ. This amino sugar then undergoes a NAD dependent oxidative deamination to produce 3,7-dideoxy-d-threo-hept-2,6-diulosonic acid which cyclizes to 3-dehydroquinate. The protein product of the M. jannaschii MJ0400 gene catalyzes the transaldolase reaction and the protein product of the MJ1249 gene catalyzes the oxidative deamination and the cyclization reactions. The DHQ is readily converted into dehydroshikimate and shikimate in M. jannaschii cell extracts, consistent with the remaining steps and genes in the pathway being the same as in the established shikimate pathway.
Jurgen Sygusch - One of the best experts on this subject based on the ideXlab platform.
-
high resolution reaction intermediates of rabbit muscle fructose 1 6 bisphosphate aldolase substrate cleavage and induced fit
Journal of Biological Chemistry, 2005Co-Authors: Miguel Stjean, Julien Lafrancevanasse, Brigitte Liotard, Jurgen SyguschAbstract:Crystal structures were determined to 1.8 A resolution of the glycolytic enzyme fructose-1,6-bis(phosphate) aldolase trapped in complex with its substrate and a competitive inhibitor, mannitol-1,6-bis(phosphate). The enzyme substrate complex corresponded to the postulated Schiff base intermediate and has reaction geometry consistent with incipient C3-C4 bond cleavage catalyzed Glu-187, which is adjacent by to the Schiff base forming Lys-229. Atom arrangement about the cleaved bond in the reaction intermediate mimics a pericyclic transition state occurring in nonenzymatic aldol condensations. Lys-146 hydrogen-bonds the substrate C4 hydroxyl and assists substrate cleavage by stabilizing the developing negative charge on the C4 hydroxyl during proton abstraction. Mannitol-1,6-bis(phosphate) forms a noncovalent complex in the active site whose binding geometry mimics the covalent carbinolamine precursor. Glu-187 hydrogen-bonds the C2 hydroxyl of the inhibitor in the enzyme complex, substantiating a proton transfer role by Glu-187 in catalyzing the conversion of the carbinolamine intermediate to Schiff base. Modeling of the acyclic substrate configuration into the active site shows Glu-187, in acid form, hydrogen-bonding both substrate C2 carbonyl and C4 hydroxyl, thereby aligning the substrate ketose for nucleophilic attack by Lys-229. The multifunctional role of Glu-187 epitomizes a canonical mechanistic feature conserved in Schiff base-forming aldolases catalyzing carbohydrate metabolism. Trapping of tagatose-1,6-bis(phosphate), a diastereoisomer of fructose 1,6-bis(phosphate), displayed stereospecific discrimination and reduced Ketohexose binding specificity. Each ligand induces homologous conformational changes in two adjacent alpha-helical regions that promote phosphate binding in the active site.
-
induced fit movements and metal cofactor selectivity of class ii aldolases structure of thermus aquaticus fructose 1 6 bisphosphate aldolase
Journal of Biological Chemistry, 2004Co-Authors: Tina Izard, Jurgen SyguschAbstract:Abstract Fructose-1,6-bisphosphate (FBP) aldolase is an essential glycolytic enzyme that reversibly cleaves its Ketohexose substrate into triose phosphates. Here we report the crystal structure of a metallo-dependent or class II FBP aldolase from an extreme thermophile, Thermus aquaticus (Taq). The quaternary structure reveals a tetramer composed of two dimers related by a 2-fold axis. Taq FBP aldolase subunits exhibit two distinct conformational states corresponding to loop regions that are in either open or closed position with respect to the active site. Loop closure remodels the disposition of chelating active site histidine residues. In subunits corresponding to the open conformation, the metal cofactor, Co2+, is sequestered in the active site, whereas for subunits in the closed conformation, the metal cation exchanges between two mutually exclusive binding loci, corresponding to a site at the active site surface and an interior site vicinal to the metal-binding site in the open conformation. Cofactor site exchange is mediated by rotations of the chelating histidine side chains that are coupled to the prior conformational change of loop closure. Sulfate anions are consistent with the location of the phosphate-binding sites of the FBP substrate and determine not only the previously unknown second phosphate-binding site but also provide a mechanism that regulates loop closure during catalysis. Modeling of FBP substrate into the active site is consistent with binding by the acyclic keto form, a minor solution species, and with the metal cofactor mediating keto bond polarization. The Taq FBP aldolase structure suggests a structural basis for different metal cofactor specificity than in Escherichia coli FBP aldolase structures, and we discuss its potential role during catalysis. Comparison with the E. coli structure also indicates a structural basis for thermostability by Taq FBP aldolase.
Yuanxia Sun - One of the best experts on this subject based on the ideXlab platform.
-
Biosynthesis of dendroketose from different carbon sources using in vitro and in vivo metabolic engineering strategies
BMC, 2018Co-Authors: Jiangang Yang, Yan Zeng, Chaoyu Tian, Yan Men, Yueming Zhu, Caixia Dong, Longhai Dai, Zhoutong Sun, Yuanxia SunAbstract:Abstract Background Asymmetric aldol-type C–C bond formation with ketones used as electrophilic receptor remains a challenging reaction for aldolases as biocatalysts. To date, only one kind of dihydroxyacetone phosphate (DHAP)-dependent aldolases has been discovered and applied to synthesize branched-chain sugars directly using DHAP and dihydroxyacetone (DHA) as substrate. However, the unstable and high-cost properties of DHAP limit large-scale application. Therefore, biosynthesis of branched-chain sugar from low-cost and abundant carbon sources is essential. Results The detailed catalytic property of l-rhamnulose-1-phosphate aldolase (RhaD) and l-fuculose-1-phosphate aldolase (FucA) from Escherichia coli in catalyzing the aldol reactions with DHA as electrophilic receptors was characterized. Furthermore, we calculated the Bürgi–Dunitz trajectory using molecular dynamics simulations, thereby revealing the original sources of the catalytic efficiency of RhaD and FucA. A multi-enzyme reaction system composed of formolase, DHA kinase, RhaD, fructose-1-phosphatase, and polyphosphate kinase was constructed to in vitro produce dendroketose, a branched-chain sugar, from one-carbon formaldehyde. The conversion rate reached 86% through employing a one-pot, two-stage reaction process. Moreover, we constructed two artificial pathways in Corynebacterium glutamicum to obtain this product in vivo starting from glucose or glycerol. Fermentation with glycerol as feedstock produced 6.4 g/L dendroketose with a yield of 0.45 mol/mol glycerol, representing 90% of the maximum theoretical value. Additionally, the dendroketose production reached 36.3 g/L with a yield of 0.46 mol/mol glucose when glucose served as the sole carbon resource. Conclusions The detailed enzyme kinetics data of the two DHAP-dependent aldolases with DHA as electrophilic receptors were presented in this study. In addition, insights into this catalytic property were given via in silico simulations. Moreover, the cost-effective synthesis of dendroketose starting from one-, three-, and six-carbon resources was achieved through in vivo and in vitro metabolic engineering strategies. This rare branched-chain Ketohexose may serve as precursor to prepare 4-hydroxymethylfurfural and branched-chain alkanes using chemical method
-
crystal structures of d psicose 3 epimerase from clostridium cellulolyticum h10 and its complex with Ketohexose sugars
Protein & Cell, 2012Co-Authors: Hsiuchien Chan, Yueming Zhu, Chunhsiang Huang, Feifei Ren, Chunchi Chen, Reyting Guo, Yuanxia SunAbstract:D-psicose 3-epimerase (DPEase) is demonstrated to be useful in the bioproduction of D-psicose, a rare hexose sugar, from D-fructose, found plenty in nature. Clostridium cellulolyticum H10 has recently been identified as a DPEase that can epimerize D-fructose to yield D-psicose with a much higher conversion rate when compared with the conventionally used DTEase. In this study, the crystal structure of the C. cellulolyticum DPEase was determined. The enzyme assembles into a tetramer and each subunit shows a (β/α)(8) TIM barrel fold with a Mn(2+) metal ion in the active site. Additional crystal structures of the enzyme in complex with substrates/products (D-psicose, D-fructose, D-tagatose and D-sorbose) were also determined. From the complex structures of C. cellulolyticum DPEase with D-psicose and D-fructose, the enzyme has much more interactions with D-psicose than D-fructose by forming more hydrogen bonds between the substrate and the active site residues. Accordingly, based on these Ketohexose-bound complex structures, a C3-O3 proton-exchange mechanism for the conversion between D-psicose and D-fructose is proposed here. These results provide a clear idea for the deprotonation/protonation roles of E150 and E244 in catalysis.
-
modification of ovalbumin with a rare Ketohexose through the maillard reaction effect on protein structure and gel properties
Journal of Agricultural and Food Chemistry, 2004Co-Authors: Yuanxia Sun, Shigeru HayakawaAbstract:The effect of nonenzymatic glycation on the structural changes and gelling properties of hen ovalbumin (OVA) through the Maillard reaction was studied. OVA was incubated at the dry state with a rare Ketohexose (d-psicose, Psi) and two alimentary sugars (d-fructose, Fru; d-glucose, Glc) at 55 °C and 65% relative humidity. To evaluate the modification of OVA by different reducing sugars during the glycation process, the extent of the Maillard reaction, aggregation processes, structural changes, and gelling behaviors were investigated. Reactivity of Psi with the protein amino groups was much lower than that of both Fru and Glc, whereas Psi induced production of browning and fluorescent substances more strongly than the two alimentary sugars did. Furthermore, OVA showed an increased tendency toward multimeric aggregation upon modifying with Psi through covalent bond. The modified OVAs with reducing sugar were similar to nonglycated control sample in Fourier transform infrared (FT-IR) characteristics, but sign...
-
modification of ovalbumin with a rare Ketohexose through the maillard reaction effect on protein structure and gel properties
Journal of Agricultural and Food Chemistry, 2004Co-Authors: Yuanxia Sun, Shigeru Hayakawa, Ken IzumoriAbstract:The effect of nonenzymatic glycation on the structural changes and gelling properties of hen ovalbumin (OVA) through the Maillard reaction was studied. OVA was incubated at the dry state with a rare Ketohexose (D-psicose, Psi) and two alimentary sugars (D-fructose, Fru; D-glucose, Glc) at 55 degrees C and 65% relative humidity. To evaluate the modification of OVA by different reducing sugars during the glycation process, the extent of the Maillard reaction, aggregation processes, structural changes, and gelling behaviors were investigated. Reactivity of Psi with the protein amino groups was much lower than that of both Fru and Glc, whereas Psi induced production of browning and fluorescent substances more strongly than the two alimentary sugars did. Furthermore, OVA showed an increased tendency toward multimeric aggregation upon modifying with Psi through covalent bond. The modified OVAs with reducing sugar were similar to nonglycated control sample in Fourier transform infrared (FT-IR) characteristics, but significantly decreased in intensity of tryptophan-related fluorescence. The results indicate that although glycation brought about similar changes in the secondary structure without great disruption of native structure, its influence on the side chains of protein in tertiary structure could be different. Breaking strength of heat-induced glycated OVA gels with Psi was markedly enhanced by the Maillard reaction. These results suggest that Psi had a strong cross-linking activity with OVA; consequently, the glycated OVA with Psi could improve gelling properties under certain controlled conditions.
Willy Malaisse - One of the best experts on this subject based on the ideXlab platform.
-
Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates: distinction of the 1-monodeutero-isotopomers of D-fructose 6-phosphate by 1H NMR spectroscopy.
Biochimie, 1991Co-Authors: Rudolph Willem, Francine Malaisse-lagae, Willy MalaisseAbstract:Abstract The 1H NMR spectrum obtained with the α- and β-anomers of d -[1-2H]fructose 6-phosphate generated from d -glucose 6-phosphate sequentially exposed in D2O to phosphoglucoisomerase, phosphoglucoisomerase, phosphofructokinase and fructose-1,6-diphosphatase differed from that recorded when the deuterated Ketohexose phosphate was produced from d -mannose 6-phosphate sequentially exposed in D2O to phosphomannoisomerase, phosphofructoctokinase and fructose-1,6-diphodphatases. The identification of the 2 isotopomers of d -fructose 6-phosphate by 1H NMR spectroscopy provides a new tool to assess the relative extent of interconversion of hexose phosphates in the reactions catalyzed by phosphoglucoisomerase and phosphomannoisomerase, respectively.
