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Nguyen H. Xuong - One of the best experts on this subject based on the ideXlab platform.
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Crystal structure of a monoclinic form of Dihydropteridine Reductase from rat liver.
Acta crystallographica. Section D Biological crystallography, 1994Co-Authors: Matthew M. Skinner, John M. Whiteley, Nguyen H. Xuong, D A Matthews, K. I. VarugheseAbstract:A binary complex of Dihydropteridine Reductase and NADH crystallizes in the space group C2, with a = 222.2, b = 46.5, c = 95.3 A and beta = 101.1 degrees. There are two dimers in the asymmetric unit. The structure was solved by molecular-replacement techniques and refined with 2.6 A data to a crystallographic R factor of 16.8%. Each dimer has twofold non-crystallographic symmetry and the four individual monomers in the asymmetric unit have the same overall molecular conformation.
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Structural and mechanistic characteristics of Dihydropteridine Reductase: a member of the Tyr-(Xaa)3-Lys-containing family of Reductases and dehydrogenases
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: K. I. Varughese, Nguyen H. Xuong, D A Matthews, P M Kiefer, John M. WhiteleyAbstract:Abstract Dihydropteridine Reductase (EC 1.6.99.7) is a member of the recently identified family of proteins known as short-chain dehydrogenases. When the x-ray structure of Dihydropteridine Reductase is correlated with conserved amino acid sequences characteristic of this enzyme class, two important common structural regions can be identified. One is close to the protein N terminus and serves as the cofactor binding site, while a second conserved feature makes up the inner surface of an alpha-helix in which a tyrosine side chain is positioned in close proximity to a lysine residue four residues downstream in the sequence. The main function of this Tyr-Lys couple may be to facilitate tyrosine hydroxyl group participation in proton transfer. Thus, it appears that there is a distinctive common mechanism for this group of short-chain or pyridine dinucleotide-dependent oxidoReductases that is different from their higher molecular weight counterparts.
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Dihydropteridine Reductase
Pteridines, 1993Co-Authors: John M. Whiteley, Kottayil I. Varughesej, Nguyen H. Xuong, David A. Matthews, Charles E. GrimshawAbstract:Summary During the past decade numerous advances have been made in understanding the structure, mechanism and clinical properties of Dihydropteridine Reductase. An attempt is made here to delineate the current status of this essential enzyme by describing its structural features, its kinetic mechanism, the cloning and expression of both rat and human enzyme forms, the solution of their crystal structures, their classification as members of a large family of short chain dehydrogenases, and finally a brief description is included indicating how current molecular biological applications have allowed the clinical definition of the aberrant form of phenylketonuria caused by a defective Reductase.
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Crystal structure of rat liver Dihydropteridine Reductase
Proceedings of the National Academy of Sciences of the United States of America, 1992Co-Authors: K. I. Varughese, John M. Whiteley, David A. Matthews, Matthew M. Skinner, Nguyen H. XuongAbstract:Abstract The structure of a binary complex of Dihydropteridine Reductase [DHPR; NAD(P)H:6,7-Dihydropteridine oxidoReductase, EC 1.6.99.7] with its cofactor, NADH, has been solved and refined to a final R factor of 15.4% by using 2.3 A diffraction data. DHPR is an alpha/beta protein with a Rossmann-type dinucleotide fold for NADH binding. Insertion of an extra threonine residue in the human enzyme is associated with severe symptoms of a variant form of phenylketonuria and maps to a tightly linked sequence of secondary-structural elements near the dimer interface. Dimerization is mediated by a four-helix bundle motif (two helices from each protomer) having an unusual right-handed twist. DHPR is structurally and mechanistically distinct from dihydrofolate Reductase, appearing to more closely resemble certain nicotinamide dinucleotide-requiring flavin-dependent enzymes, such as glutathione Reductase.
K. I. Varughese - One of the best experts on this subject based on the ideXlab platform.
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Crystal structure of a monoclinic form of Dihydropteridine Reductase from rat liver.
Acta crystallographica. Section D Biological crystallography, 1994Co-Authors: Matthew M. Skinner, John M. Whiteley, Nguyen H. Xuong, D A Matthews, K. I. VarugheseAbstract:A binary complex of Dihydropteridine Reductase and NADH crystallizes in the space group C2, with a = 222.2, b = 46.5, c = 95.3 A and beta = 101.1 degrees. There are two dimers in the asymmetric unit. The structure was solved by molecular-replacement techniques and refined with 2.6 A data to a crystallographic R factor of 16.8%. Each dimer has twofold non-crystallographic symmetry and the four individual monomers in the asymmetric unit have the same overall molecular conformation.
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Structural and mechanistic characteristics of Dihydropteridine Reductase: a member of the Tyr-(Xaa)3-Lys-containing family of Reductases and dehydrogenases
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: K. I. Varughese, Nguyen H. Xuong, D A Matthews, P M Kiefer, John M. WhiteleyAbstract:Abstract Dihydropteridine Reductase (EC 1.6.99.7) is a member of the recently identified family of proteins known as short-chain dehydrogenases. When the x-ray structure of Dihydropteridine Reductase is correlated with conserved amino acid sequences characteristic of this enzyme class, two important common structural regions can be identified. One is close to the protein N terminus and serves as the cofactor binding site, while a second conserved feature makes up the inner surface of an alpha-helix in which a tyrosine side chain is positioned in close proximity to a lysine residue four residues downstream in the sequence. The main function of this Tyr-Lys couple may be to facilitate tyrosine hydroxyl group participation in proton transfer. Thus, it appears that there is a distinctive common mechanism for this group of short-chain or pyridine dinucleotide-dependent oxidoReductases that is different from their higher molecular weight counterparts.
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Crystal structure of rat liver Dihydropteridine Reductase
Proceedings of the National Academy of Sciences of the United States of America, 1992Co-Authors: K. I. Varughese, John M. Whiteley, David A. Matthews, Matthew M. Skinner, Nguyen H. XuongAbstract:Abstract The structure of a binary complex of Dihydropteridine Reductase [DHPR; NAD(P)H:6,7-Dihydropteridine oxidoReductase, EC 1.6.99.7] with its cofactor, NADH, has been solved and refined to a final R factor of 15.4% by using 2.3 A diffraction data. DHPR is an alpha/beta protein with a Rossmann-type dinucleotide fold for NADH binding. Insertion of an extra threonine residue in the human enzyme is associated with severe symptoms of a variant form of phenylketonuria and maps to a tightly linked sequence of secondary-structural elements near the dimer interface. Dimerization is mediated by a four-helix bundle motif (two helices from each protomer) having an unusual right-handed twist. DHPR is structurally and mechanistically distinct from dihydrofolate Reductase, appearing to more closely resemble certain nicotinamide dinucleotide-requiring flavin-dependent enzymes, such as glutathione Reductase.
Richard G H Cotton - One of the best experts on this subject based on the ideXlab platform.
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Molecular basis of Dihydropteridine Reductase deficiency.
Human mutation, 1995Co-Authors: Peter M. Smooker, Richard G H CottonAbstract:The spectrum of mutations causing Dihydropteridine Reductase is reviewed. A total of 12 point mutations have been described that map in the DHPR cDNA, resulting in amino acid substitutions, insertions and premature terminations. A further two mutations are described which result in aberrant splicing of DHPR transcripts. The application of the mutation identification to diagnostics and clinical treatment is discussed.
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cys-->ser mutations in ch-human Dihydropteridine Reductase.
Advances in Experimental Medicine and Biology, 1993Co-Authors: C. M. Hardy, B. Paal, Richard G H Cotton, Holger Averdunk, Wilfred L.f. ArmaregoAbstract:The cDNA sequence of Dihydropteridine Reductase (DHPR) showed that the enzyme has four cysteine residues.1,2 These are cys26, cys85, cys104 and cys161. Evidence from titration experiments of human and rat DHPR with thiol reagents and platinum II complexes suggested that when one of the cysteines was masked by addition of NADH then it did not react with these reagents and the enzyme was protected from inactivation.3,4 In order to see if one of these cysteine residues was the proton source for the enzymic reduction of quinonoid dihydropterin substrates, we investigated the effect of replacing the cysteine residues by serine residues, which are weaker acids, and we examined the kinetics of the mutant proteins.
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Identification and in vitro expression of mutations causing Dihydropteridine Reductase deficiency.
Biochemistry, 1993Co-Authors: Peter M. Smooker, David W. Howells, Richard G H CottonAbstract:Six mutations resulting in the recessive inherited disorder Dihydropteridine Reductase deficiency are reported, five of which are previously unknown. Two are nonsense mutations, resulting in premature termination of the protein, with the remaining four being missense mutations. The mutations found lie in the middle to 3' end of the Dihydropteridine Reductase reading frame, with the exception of one mutation which lies at codon 23, which is the only mutation found in more than one patient. The mutation pattern can be described as heterogeneous. The wild type and several of the mutant DHPR cDNA's were expressed in E. coli and the proteins purified and examined by a variety of techniques, including calculation of kinetic constants. One mutation (Gly23-->Asp) results in completely inactive protein, while a second (Trp108-->Gly) has substantial activity but does not completely dimerize. Both this mutant and a third, His158-->Tyr, are extremely susceptible to in vitro protease digestion, indicating that their three-dimensional structure has been altered. The protein studies underline the heterogeneous nature of DHPR mutations, in that the effects of different amino acid substitutions on the DHPR enzyme are varied.
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Catalytic activity of tetrahydrobiopterin in Dihydropteridine Reductase deficiency and indications for treatment
Pediatric research, 1993Co-Authors: Alberto Ponzone, Ornella Guardamagna, Irma Dianzani, Riccardo Ponzone, Giovanni Battista Ferrero, Marco Spada, Richard G H CottonAbstract:Catalytic Activity of Tetrahydrobiopterin in Dihydropteridine Reductase Deficiency and Indications for Treatment
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The spectrum of mutations in Dihydropteridine Reductase deficiency.
Advances in experimental medicine and biology, 1993Co-Authors: Peter M. Smooker, Irma Dianzani, David W. Howells, Richard G H CottonAbstract:Dihydropteridine Reductase (DHPR, EC 1.6.99.7) is the enzyme required for the recycling of tetrahydrobiopterin, an essential cofactor of the three aromatic amino acid hydroxylases (1). A rare inherited disorder is due to a deficiency of this enzyme, resulting in hyperphenylalanemia and disorders of dopamine and serotonin metabolism. DHPR-deficiency was recognized as an inheritable disorder, distinct from PKU, in the 1960’s, and the disease state was later correlated with an absence of enzyme activity in cultured fibroblasts (2). This lack of enzymatic activity was shown in some cases to be due to an absence of protein.
Wilfred L.f. Armarego - One of the best experts on this subject based on the ideXlab platform.
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cys-->ser mutations in ch-human Dihydropteridine Reductase.
Advances in Experimental Medicine and Biology, 1993Co-Authors: C. M. Hardy, B. Paal, Richard G H Cotton, Holger Averdunk, Wilfred L.f. ArmaregoAbstract:The cDNA sequence of Dihydropteridine Reductase (DHPR) showed that the enzyme has four cysteine residues.1,2 These are cys26, cys85, cys104 and cys161. Evidence from titration experiments of human and rat DHPR with thiol reagents and platinum II complexes suggested that when one of the cysteines was masked by addition of NADH then it did not react with these reagents and the enzyme was protected from inactivation.3,4 In order to see if one of these cysteine residues was the proton source for the enzymic reduction of quinonoid dihydropterin substrates, we investigated the effect of replacing the cysteine residues by serine residues, which are weaker acids, and we examined the kinetics of the mutant proteins.
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New Inhibitors of Dihydropteridine Reductase (Human Brain)
Advances in experimental medicine and biology, 1993Co-Authors: David Randles, Hiroyasu Taguchi, Wilfred L.f. ArmaregoAbstract:The Dihydropteridine Reductase (DHPR) gene from rat liver has recently been cloned1 and the protein that was expressed from the cDNA was crystallised as the binary DHPR-NADH complex.2 The X-ray structure of the enzyme was determined and although the exact location of NADH in the enzyme was determined in the binary complex, the precise position of the pteridine cofactor was not obtained and had to be deduced from known kinetic data of various pteridine cofactor analogues.2 In order to obtain the precise position of the pteridine cofactor it is necessary to crystallise the ternary complex of DHPR, NADH and an inhibitor whose structure is so close to that of a viable cofactor (eg 1) that it would bind at the active site in the same manner as the pterin.
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Dihydropteridine Reductase from Escherichia coli exhibits dihydrofolate Reductase activity.
Biological chemistry Hoppe-Seyler, 1992Co-Authors: S. G. Vasudevan, B. Paal, Wilfred L.f. ArmaregoAbstract:E. coli Dihydropteridine Reductase, known to have a pterin-independent oxidoReductase activity with potassium ferricyanide as electron donor, has now been shown to possess also dihydrofolate Reductase activity. The kinetic parameters for dihydrofolate Reductase activity have been determined. The ratio of the three activities, Dihydropteridine Reductase, dihydrofolate Reductase and pterin-independent oxidoReductase activity is 1.0, 0.05 and 4.3, respectively. The enzyme, a flavoprotein which is unstable in the presence of dithiothreitol, was shown to be a monomer with a molecular mass of 25.7 kDa. The apparent lack of discrimination between hydride transfer from the pyridine nucleotide to N5 of the pterin in the Dihydropteridine Reductase reaction and C6 of folate in the dihydrofolate reaction suggested that the FAD prosthetic group may be involved in the hydride transfers. The flavoprotein inhibitor N,N- dimethylpropargylamine inhibited the Dihydropteridine Reductase and oxidoReductase reactions differently and did not affect the dihydrofolate Reductase activity however.
John M. Whiteley - One of the best experts on this subject based on the ideXlab platform.
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Crystal structure of a monoclinic form of Dihydropteridine Reductase from rat liver.
Acta crystallographica. Section D Biological crystallography, 1994Co-Authors: Matthew M. Skinner, John M. Whiteley, Nguyen H. Xuong, D A Matthews, K. I. VarugheseAbstract:A binary complex of Dihydropteridine Reductase and NADH crystallizes in the space group C2, with a = 222.2, b = 46.5, c = 95.3 A and beta = 101.1 degrees. There are two dimers in the asymmetric unit. The structure was solved by molecular-replacement techniques and refined with 2.6 A data to a crystallographic R factor of 16.8%. Each dimer has twofold non-crystallographic symmetry and the four individual monomers in the asymmetric unit have the same overall molecular conformation.
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Structural and mechanistic characteristics of Dihydropteridine Reductase: a member of the Tyr-(Xaa)3-Lys-containing family of Reductases and dehydrogenases
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: K. I. Varughese, Nguyen H. Xuong, D A Matthews, P M Kiefer, John M. WhiteleyAbstract:Abstract Dihydropteridine Reductase (EC 1.6.99.7) is a member of the recently identified family of proteins known as short-chain dehydrogenases. When the x-ray structure of Dihydropteridine Reductase is correlated with conserved amino acid sequences characteristic of this enzyme class, two important common structural regions can be identified. One is close to the protein N terminus and serves as the cofactor binding site, while a second conserved feature makes up the inner surface of an alpha-helix in which a tyrosine side chain is positioned in close proximity to a lysine residue four residues downstream in the sequence. The main function of this Tyr-Lys couple may be to facilitate tyrosine hydroxyl group participation in proton transfer. Thus, it appears that there is a distinctive common mechanism for this group of short-chain or pyridine dinucleotide-dependent oxidoReductases that is different from their higher molecular weight counterparts.
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Dihydropteridine Reductase
Pteridines, 1993Co-Authors: John M. Whiteley, Kottayil I. Varughesej, Nguyen H. Xuong, David A. Matthews, Charles E. GrimshawAbstract:Summary During the past decade numerous advances have been made in understanding the structure, mechanism and clinical properties of Dihydropteridine Reductase. An attempt is made here to delineate the current status of this essential enzyme by describing its structural features, its kinetic mechanism, the cloning and expression of both rat and human enzyme forms, the solution of their crystal structures, their classification as members of a large family of short chain dehydrogenases, and finally a brief description is included indicating how current molecular biological applications have allowed the clinical definition of the aberrant form of phenylketonuria caused by a defective Reductase.
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Crystal structure of rat liver Dihydropteridine Reductase
Proceedings of the National Academy of Sciences of the United States of America, 1992Co-Authors: K. I. Varughese, John M. Whiteley, David A. Matthews, Matthew M. Skinner, Nguyen H. XuongAbstract:Abstract The structure of a binary complex of Dihydropteridine Reductase [DHPR; NAD(P)H:6,7-Dihydropteridine oxidoReductase, EC 1.6.99.7] with its cofactor, NADH, has been solved and refined to a final R factor of 15.4% by using 2.3 A diffraction data. DHPR is an alpha/beta protein with a Rossmann-type dinucleotide fold for NADH binding. Insertion of an extra threonine residue in the human enzyme is associated with severe symptoms of a variant form of phenylketonuria and maps to a tightly linked sequence of secondary-structural elements near the dimer interface. Dimerization is mediated by a four-helix bundle motif (two helices from each protomer) having an unusual right-handed twist. DHPR is structurally and mechanistically distinct from dihydrofolate Reductase, appearing to more closely resemble certain nicotinamide dinucleotide-requiring flavin-dependent enzymes, such as glutathione Reductase.